Title of Invention	STABILIZED MAGNETIC EMULSION OF OIL-IN-WATER TYPE AND PROCESS OF PREPARING THE SAME
Abstract	A stabilized magnetic emulsion of oil-in-water type comprising (i) 1-40 wt. %, preferably 7-14 wt. % of a ferrofluid emulsion ; (ii) 47- 98.95 wt. %, preferably 82.5- 92.5 wt. % of an aqueous phase (iii) 0.001-5 wt. %, preferablyr0.01- 1.5 wt. % of an emulsifying agent selected from anionic, cationic and non ionic surfactant and mixtures.theREof; and (iv) 0.05-8.0 wt. %, preferably 0.5-2.0 wt. % of a block copolymer with hydrophobic and hydrophilic groups with a molecular weight ranging from 4000 to 4 00 000.

Title of Invention

STABILIZED MAGNETIC EMULSION OF OIL-IN-WATER TYPE AND PROCESS OF PREPARING THE SAME

Abstract

A stabilized magnetic emulsion of oil-in-water type comprising (i) 1-40 wt. %, preferably 7-14 wt. % of a ferrofluid emulsion ; (ii) 47- 98.95 wt. %, preferably 82.5- 92.5 wt. % of an aqueous phase (iii) 0.001-5 wt. %, preferablyr0.01- 1.5 wt. % of an emulsifying agent selected from anionic, cationic and non ionic surfactant and mixtures.theREof; and (iv) 0.05-8.0 wt. %, preferably 0.5-2.0 wt. % of a block copolymer with hydrophobic and hydrophilic groups with a molecular weight ranging from 4000 to 4 00 000.

Full Text	FORM 2 THE PATENTS ACT 1970 (39 of 1970) COMPLETE SPECIFICATION ( See section 10; rule 13). TITLE " Stabilized magnetic emulsion of ail-in-water and present of preparing the name" APLICANT Department of Atomic Energy Government of India, Department of the Govt, of India, having its office at Anushakthi Bhavan , Chathrapathy Shivaji Maharaj Marg, Mumbai, 400001, Maharashtra , India The following specification describes the nature of the invention and the manner in which it is to be performed 19-12-2002 GRANTED 1 Field of Invention The present invention relates to a stabilized magnetic emulsion and .a process of making it. The present invention particularly relates to magnetic emulsions known as ferrofluid emulsions, which are useful in non-destructive devices, sensors, optical filters etc Background and Prior Art Magnetic liquid, or ferrofluid oil is suspensions of ferromagnetic particles in a liquid carrier. Nanometer sized magnetite particles suspended in an organic liquid such as kerosene, octane. The particles are coated with a surfactant (called inner surfactant) such as oleic acid, phosphoric acid, to prevent flocculation of the particles of ferrofluid. Typically, the sizes of the particle are below 15 run. R E Rosenweig has described their preparation, properties and uses in an article in International Science and Technology, July 1966, pp. 45 -56. Preparations and usefulness of magnetic (ferrofluid) oil have also been described by R E Rosenweig in the book titled "Ferrodynamics", 1985, Cambridge University Press, N Y. A direct ferrofluid emulsion consists of ferrofluid oil, a water-soluble surfactant (called outer surfactant) and a continuous phase of water. Here, the oil droplets are dispersed in a continuous phase of water. Typically, the size of the droplets is of the order of 100 run to a few microns. Preparation of a typical ferrofluid emulsion has been described by J Philip et al., in Measurement Science and Technology Volume 10, Year 1999, pp N71-N75, as follows: i. Mix slowly sodium dodecyl sulphate (SDS)(5 g) and water (5 g); ii. Add ferrofluid oil (90 g) to the above solution to get w/o emulsion with very large droplets of diameter 10 (µm or more; iii. Then mix it thoroughly in a colloid mixer to obtain o/w emulsion with droplet diameter in the range of 0.1 to 1 µm; iv. Dilute it further with water to get a final SDS level in the emulsion 2.3 g 1"'. Such a ferrofluid is an oil-in-water emulsion, which has been employed for detecting defects in ferromagnetic materials and components described inund. Pat. Nos. 186620 & /186574}by a method called magnetic flux leakage probe. 2 In these methods, monodispersed ferrofluid is confined between two thin transparent glass slides and a white light source for illumination. It has been shown that by employing ferrofluid droplets of suitable size and surfactant concentration, one can qualitatively identify the region where the defect is located in the test specimen by visually observing a color change in the ferrofluid cell, in the vicinity of a crack or defect in the test specimen. The second patent-(Ind. 186620) reveals a technique to quantify the defect characterization based on a spectrograph-based system, which precisely computes the Bragg peak wavelength that is related to the crack size and position. The ferrofluid emulsions employed in the optical probes disclosed in the above patents, often deteriorates after prolonged use, under harsh environments. As a result, the emulsion, sometimes, is destabilized after a few months of use, and it becomes necessary to replace it with fresh emulsion at regular intervals of time. Emulsions used in those probes were stabilized either electrostatically of sterically but both these stabilization techniques were not very effective for long term stability. There are no such stabilized systems (oil-in-water type of emulsion with solid magnetic particles inside the oily phase) described in the prior art. Other prior art disclosing stabilization of other emulsions are: (US patent 6,074,470/ discloses a stable aqueous silane emulsion with constant particle size. The emulsion comprises a continuous water phase, a discontinuous silane phase, and an emulsifier system. D. H. Napper, has reviewed the subject of stabilization of emulsions in general, in 1987, in his book titled Polymeric Stabilization of Colloidal Dispersions; Marcel Dekker: New York, 1987. There are also a few other reviews on polymeric stabilizations, e.g.; Th. Tadors 1988 Polymers in colloidal systems, Elsevier: Amsterdam etc. J N Isrelachvili, 1985 Intermodular and Surface Forces, San Diego: Academic Press. Steric stabilization techniques are used in numerous industrial applications such as paints, toners, emulsions, cosmetics, pharmaceuticals, processed food, lubricants etc. For example((US patent 6,346,256 discloses an oil/water/oil emulsion stabilized with at least one partially or completely cross-linked organopolysiloxane elastomer having at least one polyoxyethylenated and/or polyoxypropylenated chain. Some of the other example for steric stabilizations, methods.-employed in various formulations, ^disclosed in US patents\ are 5,153,233, 5,438,088, 6,346,600, 5,507,804 etc. 3 '■■!..* - In the case of electrostatic stabilization, ionic/ nonionic ^surfactants are employed. The electrostatically stabilized colloids often coagulate wheh, the .ionic'-strength of the. medium is increased sufficiently high, due to the reduction in the, spatial, extension of electrical double layers. For example, an ionic strength higher than O.OOIM, 'corresponds to a length of about lOnm for a 1:1 electrolyte that can lead to van der Waals attraction in the dispersion. This is the range where electrostatic stabilization often fails. For certain emulsions electro-steric stabilizations have been reported in which polyelectrolytes have been employed, but there is no relevant prior art that provides a systematic method to improve stability of such emulsions, there is no guideline to impart long-range repulsion between the colloidal particles; particularly water-in-oil emulsions of the ferrofluid described above. Object The principal object of the invention is to obtain a well-stabilized ferrofluid emulsion [oil-in-water] that can be reused a number of times in optical probes especially those described in aforesaid Indian Patent specification Nos.I86620 & 186574. Summary of the Invention Accordingly, the present invention provides a stabilized magnetic emulsion of oil-in-water type comprising: (i) 1-40 wt. %, preferably 7-14 wt. % of a ferrofluid emulsion ; (ii) 47- 98.95 wt. %, preferably 82.5- 92.5 wt. % of an aqueous phase (iii) 0.001-5 wt. %, preferably 0.01- 1.5 wt. % of an emulsifying agent selected from anionic, cationic and non ionic surfactant and mixtures thereof; and (iv) 0.05-8.0 wt. %, preferably 0.5-2.0 wt. % of a block copolymer with hydrophobic and hydrophilic groups with a molecular weight ranging from 4000 to 4 00 000. and a process of preparing said stabilized magnetic emulsion of oil-in-water type comprising (i) preparing an emulsion by slowly adding oily phase into a premixed surfactant - water mixture and shearing it in an emulsifier to get a crude emulsion; (ii) diluting the said crude emulsion repetitively with water containing surfactant at CMC and fractionating the said crude emulsion to obtain monodispersed emulsion with droplet size in the range of 100-1000 nm. 4 (iii) adding said block copolymer into the said .crude emulsion and incubating at 25°C for atleast 72 hrs. (iv) adding further amount of same or different surfactant to the incubated crude emulsion, obtained at the end of step 3 and mixing them thoroughly, (v) incubating the emulsion obtained at the end of step (iv) at 25-3~5°C for a further period of atleast 1 hr to obtain a stabilized magnetic emulsion. It is preferable to carry out the shearing in step (i) at rpm of 500 to 1000 for about 30 minutes and the further amount of surfactant in step (iv) is 0.001 to 5 wt %; preferably 0.01 to 01.5 wt% of the said crude emulsion. Detailed description of the Invention: The size of said magnetic particles inside the stabilized emulsion of the present invention varies from 5-15 nm, preferably it is in the range of 7-10 nm. The inner surfactant used is chosen from oleic acid, phosphoric acid etc. The carrier used is chosen from oils such as octane, cyclohexane, kerosene. The surfactant is chosen from anionic, cationic or non-ionic types, which are well known in the field. The anionic surfactant are chosen from surfactants such as polyoxyethylene, alkylphenyl ether sulfates, polyoxyethylene styrenated phenyl ether sulfates, alkylphosphates, polyoxyethylene alkyl ether phosphates, polyoxyethylene alkylphenyl ether phosphates, fatty acid salts, alkylbenzene sulfonates, alkyl sulfonates, alkyl naphthalene sulfonates, alpha -olefin sulfonates, dialkyl sulfosuccinates, alpha -sulfonated fatty acid salts, N-acyl-N-methyllaurate, alkylsulfates (e.g. SDS), sulfated lipids, polyoxyethylene alkyl ether sulfates and naphthalene sulfonate formaldehyde condensates. The cationic surfactant^ is chosen from alkyltrimethyl ammonium salts (e.g. CTAB, TTAB), primary to tertiary aliphatic amine salts, dialkyldimethyl ammonium salts, trialkylbenzyl ammonium salts, alkyl pyridinium salts, tetraalkyl ammonium salts, and polyethylene polyamine fatty acid amide salts. The nonionic surfactant is such as polyoxyethylene polyoxypropylene glycols, polyoxyethylene polyoxypropylene alkyl ethers, polyoxyethylene alkyl ethers, polyoxyethylene alkenyl ethers, polyoxyethylene alkylphenyl ethers (e.g. NP10), 5 polyoxyethylene polystyrylphenyl ethers, polyhydric alcohol fatty acid partial' esters, sorbitan fatty acid esters, glycerol fatty acid esters, deca-glycerol fatty acid esters,, polyglycerol fatty acid esters, propylene glycol pentaerythritol fatty acid esters, polyoxyethylene sorbitan fatty acid esters, polyoxyethylene glycerol fatty acid esters, polyoxyethylene polyhydric alcohol fatty acid partial esters, polyoxyethylene fatty acid esters, polyglycerol fatty acid esters, polyoxyethylenated castor oil, fatty acid diethanolamides, polyoxyethylene alkylamines, triethanolamine fatty acid partial esters, trialkylamine oxides, and polyoxyalkylene group containing organopolysiloxanes. A block copolymer with a hydrophobic group such as vinyl acetate, polysiloxane groups, polyfluro alkyl groups, legnine derivatives, poly propylene glycol derivatives, polybutylene oxide etc. and a hydrophilic group such as poly vinyl alcohol, poly saccharide, starch, cellulose, polyurethane, polyethelyne oxide etc. with a molecular weight ranging from 4000 to 4 00 000. The ratio of hydrophobic and hydrophilic group can range from 5:95, preferably from 10:90 and more preferably in the range of 20:80. The block copolymer used is preferably, polyvinyl alcohol (88 wt%) with vinyl acetate (12 wt%). The crude emulsion obtained at the end of step 1 is fractionated* to obtain a monodispersed emulsion with a droplet size in the range of 100 - 1000 nm. Then the steps (ii) to (viii) are repeated to obtain a stabilized monodispered emulsion. Fractionation is a process to obtain monodispersed emulsion droplets. When surfactant concentration is above a critical micellar concentration, the emulsions droplets begin to flocculate or cream due to depletion flocculation induced by the non-adsorbed surfactant. In an emulsion containing droplets of the order of hundreds of nanometer, the non-adsorbed surfactant forms the aggregates of the order of a few nanometers. When the emulsion droplets approach closer the thickness of the continuous phase film becomes smaller and smaller and when it is smaller than the micelle diameter micelles are expelled from the thin film. So the thin film region experiences a large activity of the solvent than the surroundings and an osmotic pressure develops pushing the droplets closer. On addition of surfactant to a critical concentration to a typical polydispersed O/W emulsion, the dense phase of aggregated oil droplets separates from a dilute phase of free droplets. At the flocculation threshold the dense phase contains most of the bigger droplets and the dilute phase mainly smaller ones. First step the dilute phase is separated and the dense 6 phase is again diluted with more surfactant. The above process is repeated several times to obtain monodisperesed emulsion and this process is well known in the field. For the purpose of this invention, a 'stable' emulsion is defined as (1) an emulsion having no phase separation and no formation of sediment or a layer of cream, or (2) if formation of sediment or a layer of cream does occur, the emulsion can be obtained by simple shaking or stirring with no loss of effects. The stability of such emulsions prepared by the above process is tested by force apparatus, microscopic and macroscopic observations at regular intervals of time. An optical phase contrast microscope (M/s Leica DM IRM) equipped with a digital camera (JVC) and imaging software (Leica) has been used for observing the emulsion droplets. Force experiments have been performed using a home built force apparatus, which allow measurement of forces between individual emulsion droplets. These methods are described in our co-pending Ind. Pat. Application. No. 501/Mum/02. Examples: The invention will now be illustrated with the help of a few examples. The examples are by way of illustration only and in no way restrict the scope of the invention. Examples I and II are not of the present invention; Examples HI - VTA are of the present invention. Drawings Flow Chart 1 : A flowchart of process of the present invention in general and that used in the Examples III-VIII. The processes of Examples I and II are experiments on prior art, using either surfactant or polymer. The above examples are used for comparing the stability of the samples that are prepared using the newly invented process, with prior art processes. Variation of force (N) Vs inter-droplet spacing (ran), in the presence of surfactant and polymer systems are shown in Fig 1: for PVA of 40K (0.68wt%) for different SDS concentrations ( 0.0046wt% to 1.152 wt%). (Based on the data given in Table 1 and Example IIII) Fig 2 :for PVA of 115K (0.49wt%) for different SDS concentrations ( 0.0034wt% to 0.28 wt%). (Based on the data given in Table 1 and Example IV) Fig 3 :for PVA of 155K (0.45wt%) for different SDS concentrations ( 0.0033 wt% to 0.126 wt%). (Based on the data given in Table 1 and Example V) Fig 4 : for PVA of 155K (0.45wt%) for different SDS concentrations (1.6mM up to 10 Months). (Based on the data given in Table 1 and Example V) 7 Fig 5 : for PVA of 155K (0.43wt%) for different CTAB concentrations ( 0.0002 wt% to 0.0245wt%). (Based on the data given in Table 1 and Example VI) Fig 6 : for PVA of 155K (0.5wt%) for CTAB 9mM up to 10 months storage. (Based on the data given in Table 1 and Example VI) Fig 7 : for PVA of 155K (0.5wt%) for TTAB 5. ImM up'to 10 months storage. (Based on the data given in Table 1 and Example VTI). Fig 8 : for PVA of 155K (0.5wt%) for NP10 5.0 mM up to 10 months storage. (Based on the data given in Table 1 and Example VTH). Materials used for the examples : Ferrofluid emulsion Ferrofluid emulsion was prepared by mixing 5 part of surfactant with 5 parts of water until the surfactant was completely mixed with the water. The outer surfactant used in the experiment was SDS. The ratio of SDS, water and ferrofluid oil was 5:5:90. Then 90 parts of the octane based ferrofluid oil is added to the above surfactant-water mixture. The resulting mixture was stirred at 500 RPM with a 1-inch diameter blade for 20 minutes. Aqueous phase : Water -triply distilled. Surfactant The anionic surfactant: sodium dodecyl sulphate (C12H25-SO4 Na), hereafter described as SDS. The cationic surfactants: -Cetyltrimethyl ammonium bromide (CTAB), and Tetradecyltrimethyl ammonium bromide (TTAB). The nonionic surfactant : nonyl phenol ethoxylate (NP10). SDS, CTAB.TTAB, NP10 etc. obtained from Sigma, USA. The purity of all the surfactants was about 99.9 %. Polymer: The polymer used in these experiments was a statistical copolymer of vinyl alcohol (CH2CHOH -88 wt%.) and vinyl acetate (CH (OCOCH3)-12 wt%), which is randomly distributed along the polymer chain, of three average molecular weights of 40000, 115000 and 155000 (here after referred as PVA 40K, 115K and 155K respectively). The Polyelectrolyte used in our experiment was polyacrylic acid (PAA). PVA 40K, 115K and 155K; and the polymers were obtained from Aldrich, USA. Weak Polyelectrolytes : Polyacrylic acid (PAA) 120K, 250K (Aldrich, USA) Stabilized Ferrofluid Emulsion Composition: The composition of the ferrofluid oil, used in all the examples is the same (i.e. 45 wt% of 8 run sized Fe304 coated with oleic acid (less than 1 wt%) in 54 wt% of octane). 8 The basic composition of the un-stabilized ferrofluid emulsion is the same in all the cases (i.e. ferrofluid oil-in-water emulsion 9.8 wt%, aqueous phase 90 wt% and surfactant (SDS) 0.004 wt%. The compositions of emulsions prepared in these examples are given in Table 1. Table 1: Ferrofluid Emulsion Compositions Example 1:Surfactant Only (SDS) Surf. mM Surf. (wt%) PVA (wt%) FF (wt%) water (wt%) debye length (nm) 2Lo(nm) 0.571 - 0.016 0 9.8 90.18 12.9 64 0.756 0.021 0 9.8 90.179 10.9 56 1 0.028 0 9.8 90.172 9.3 52 1.51 0.043 0 9.8 90.15 7.8 46 3.02 0.086 0 9.$ $0.11\| 6.2 39 7.56 0.217 0 9.8 89.98 2.85 22 Example 2: Polymer Only-PVA40K Surf. mM Surf. (wt%) PVA-vac (wt%) FF (wt%) water (wt%) debye length (nm) 2Lo(nm) 0 0 0.68 10 89.32 5.9 29.5 o; 0 0.5 1o; 89.50 111.7 62 0 0 0.52 10 89.48 13.4 73 Example 3:40K+ SDS Surf. mM Surf. (wt%) PVA-vac (wt%) FF (wt%) water (wt%) debye length (nm) 2Lo(nm) , 0 0 0.68 11 88.32 5.9 29.5 16 0.00460 0.68 11 87.85 5.81 33 0.26 0.007 0.68 11 88.31 6.15 36.5 0.8 0.023 0.68 11 88.29 6.9 44 1.6 0.046 0.68 11 88.27 7.1 56 3.2 0.092 0.68 11 88.22 7.8 66 8 0.230 0.68 11 88.08 7.2 72 24 0.691 0.68 11 87.62 6.6 74 40 1.152 0.68 11 87.16 6.6 75 Example 4:115K+SDS Surf. mM Surf. (wt%) PVA-vac (wt%) FF (wt%) water (wt%) debye length (nm) 2Lo(nm) 0 0 0.49 9.6 89.91 11.57 57 0.12 0.0034 0.49 9.6 89.90 11.8 64 0.236 0.0067 0.49 9.6 89.90 11.8 66 0.386 0.0111 0.49 9.6 89.89 12.1 67.5 0.81 0.0233 0.49 9.6 89.88 14.16 80 2.4 0.0691 0.49 9.6 89.84 14 111 3.94 0.1134 0.4$ 96 89.79, 13.6 125 8.1 0.2332 0.49 9.6 89.67 12.8 142 9.8 0.2822 0.49 9.6 89.62 12.3 160 9 Example 5:155K+ SDS Surf. mM Surf. (wt%) PVA-vac (wt%) FF (wt%) water (wt%) debye length (nm) 2Lo(nm) 0 0 0.45 11 88.55 13.24 73 0.118 0.0033 0.45 11 88.54 10.63 69 0.29 0.0083 0.45 11 88.54 13.8 77 0.53 0.0152 0.45 11 88.53 115.9; 91! 0.8 0.0230 0.45 11 88.52 15.9 106 1.6 0.0460 0.45 11 88.50 15.38 133 4.4 0.1267 0.45 11 88.42 13.47 158 Example 6- 155K+CTAB Surf. mM Surf. (wt%) PVA-vac (wt%) FF (wt%) water (wt%) debye lenqth (nm) 2Lo(nm) 0 0 0.43 10 89.57 12.418 60 0.06 0.0002 0.43 10 89.56 9.99 60 0.225 0.0008 0.43 10 89.56 9.951 60 0.68 0.0024 0.43 10 89.56 11.186 60 0.9 0.0032 0.43 10 89.56 11.148 62 1.35 0.0049 0.43 10 89.56 12.225 65 1.8 0.0065 0.43 10 89.56 14.327 75 2.25 0.0081 0.43 10 89.56 15.442 95 2.7 0.0098 0.43 10 89.56 16.077 105 3.15 0.0114 0.43 10 89.55 15.535 113 4.05 0.0147 0.43. 10 89.55 15.385 125 4.95 0.0180 0.43 10 89.55 14.286 135 5.85 0.0212 0.43 10 89.54 14.43 145 6.75 0.0245 0.43 10 89.54 14.124 151 Example 7- 155K+TTAB Surf. mM Surf. (wt%) PVA-vac (wt%) FF (wt%) water (wt%) debye length (nm) 2Lo(nm) 0 0 0.5 12 87.5 53 .0875 0.0029 0.5 12 87.49 9.505 55 0.175 0.0058 0.5 12 87.49 9.7182 60 0.35 0.0117 0.5 12 87.48 9.5511 61 1.4 0.0470 0.5 12 87.45 11.601 62 2.1 0.0706 0.5 12 87.42 13.089 70 2.8 0.0941 0.5 12 87.40 14.327 85 3.5 0.1177 0.5 12 87.38 15.198 103 4.375 0.1471 0.5 12 87.35 15.625 117 5.25 0.1766 0.5 12 87.32 15.06 130 6.125 0.2060 0.5 12 87.29 14.514 135 7.0 0.2354 0.5 12 87.26 13.69 142 8.75 0.2943 0.5 12 87.20 13.1 152 10 Example8- 155K-NP10 Surf. mM Surf. (wt%) PVA -Vac (wt%) FF (wt%) water (wt%) debye length (nm) 2Lo(nm) 0.0000125 0.000826 0.5 12 87.49917 10.6383 .55 0.000025 0.001652 0.5 12 87.49835 10 56 0.00005 0.003304 0.5 12 87.4967 10.10101 57 0.00015 0.009912 0.5 12 87.49009 10.52632 60 0.00025 0.01652 0.5 12 87.48348 10.41667 63 0.0005 0.03304 0.5 12 87.46696 10.20408 66 0.0012 0.079296 0.5 12 87.4207 10.23541 70 0.0025 0.1652 0.5 12 87.3348 10.46025 70 0.005 0.3304 0.5 12 87.1696 10.4 70.2 0.0075 0.4956 0.5 12 87.0044 10.3 69.5 The compositions marked in bold letters in each tables were further studied for their shelf life by actual storage and the results are shown in table 2. Process of Manufacture of Stabilized Ferrofluid Emulsion. The various compositions of Examples I-VII shown in Table 1 were prepared by the process described as per flow chart 1. Ferrofluid emulsion was prepared by mixing 10 part of surfactant with 10 parts of water until the surfactant was completely mixed with water. The surfactant used in the Examples I -V was SDS. In Example VI and VHI it was CTAB , TTAB and NP10 respectively. The ferrofluid oil contains 10% of Fe304 grains with average grain size of 8nm. The resulting mixture was stirred at 500 RPM, with a 1-inch diameter blade for 30 minutes, using an emulsifier [REMI-RQ122, India). After 30 minutes, the mixture was diluted with water. The resulting mixture was poured into a cylindrical measuring jar. After this process a crude emulsion with wide size distribution was obtained, which was size selected using the fractionation approach mentioned earlier. Then the surfactant concentration of the size-selected emulsion was fixed at cmc/40 (below this value the emulsion becomes destabilized) by dilution with triply distilled water. The required quantity of macromoleeules (PVA) was introduced into the colloidal system and stirred until the macromoleeules were mixed properly with colloidal droplets. The whole system was incubated for at least 72 hrs. (in Example 1 polymer was not added). After reaching equilibrium, the surfactants of required values were add and the system was well stirred. The colloidal suspension was kept for a few hours [maximum 2 hours] to reach the equilibrium conditions. The system can then be used for various applications. 11 Stabilization Studies : The stabilization of the ferrofluid emulsions prepared in the above Examples I-III with compositions as given in Table 1, were studied by the force measurement procedure described in the Indian Patent Application No. 501/MUM/02. The system is later used for our experiments to check the stability tests using microscopic, macroscopic approaches. The optimum value of the macromolecule and the surfactant concentration have been measured quantitatively using our force measurement apparatus, which enabled us the estimation of onset of repulsion and the magnitude of force for a given ratio of macromolecule and surfactant concentration. The exact quality of the formulations has also been tested by other means such as turbidity or macroscopic phase separation as a function of time. The results are given in Table 2. These results show that the stability of emulsions stabilized using the above approach was far superior compared to those stabilized electro or steric (prior art) methods. Stability as Shelf life studies A representative sample of each Examples I-VTfl with compositions as shown in Table 2 have been prepared and kept in vials and the stability of emulsions was observed at various time intervals. The stability test results are tabulated in Table 2 12 Exa¬mple Sample Time (month) Microscopy Macroscopic Force Apparatus (Magnetic field induced chaining) I. Surfactant stabilized with 3.02 mM SDS 1 No flocs Single phase# stable 3 Few flocs Almost single unstable 5 IA** Two phase ## - 8 IA Two phase - 10 IA Two phase - II PVA-Vac stabilized with 40K, at 0.5% 1 No flocs Single phase stable 3 No flocs Single phase stable 5 IA Two phase - 8 IA Two phase - 10 IA Two phase - III PVA-Vac (40K, 0.68%) and SDS (3.2 mM) 1 No flocs Single phase stable 3 No flocs Single phase stable 5 No flocs Single phase stable 8 No flocs Single phase stable 10 No flocs Single phase stable IV PVA-Vac(115K, 0.68%) and SDS (3.94mM) 1 No flocs Single phase stable 3 No flocs Single phase stable 5 No flocs Single phase stable 8 No flocs Single phase stable 10 No flocs Single phase stable V PVA-Vac (155K, 0.45%) and SDS (4.4 mM) 1 No flocs Single phase stable 3 No flocs Single phase stable 5 No flocs Single phase stable 8 No flocs Single phase stable 10 No flocs Single phase- stable VI PVA-Vac (155K, 0.43%) and CTAB (4.05 mM) 1 No flocs Single phase stable 3 No flocs Single phase stable 5 No flocs Single phase stable 8 No flocs Single phase stable 10 No flocs Single phase stable VII PVA-Vac(155K, 0.5%) and TTAB (8.7 mM) 1 No flocs Single phase stable 3 No flocs Single phase stable 5 No flocs Single phase stable 8 No flocs Single phase stable 10 No flocs Single phase stable VIII PVA-Vac(155K, 0.5%) and NP10 (15 mM) 1 No flocs Single phase stable 3 No flocs Single phase stable 5 No flocs Single phase stable 8 No flocs Single phase stable 10 No flocs Single phase stable No Floes, means no particle aggregates and the emulsion is perfectly stable. *IA means the droplets form irreversible aggregates and the emulsion becomes completely destabilized. #Single phase means the emulsion is perfectly stable ##Two phase means oil and water phases separate and the system becomes destabilized. 13 Our observations on the results of these tests in respect of each of these examples are given below: ' Details of the force experimental technique and the interpretation of force results with respect to the stability of the emulsion is briefly discussed below: As the ferrofluid droplets are super paramagnetic in nature, an applied field induces a magnetic dipole in each drop, causing them to form chains. The magnitude of the induced dipole is controlled by the strength of the applied field. At low concentrations, one droplet thick chains are well separated and oriented along the field direction. Due to the presence of the one-dimensional ordered structure, a Bragg peak can be observed, from which the inter-droplet separation (h) can be estimated precisely, using a spectrograph. The condition for forming a linear chain is that the repulsive force between the droplets must exactly balance the attractive force between the droplets induced by the applied magnetic field. The sensitivity in the distance measurement, in our experimental set up, was 0.1 nm. The range of force that can be probed using this technique is 10"1 N to 10",13N. From the force profiles, we deduce three parameters- A, from the slope, the first interaction length or onset of repulsion (2Lo) defined as the distance at which the magnitude of force is 2xl0"13 N and the magnitude of force (k). In the case of surfactant stabilized colloids, the force profiles have been found to be exponentially decaying, where the magnitude (k) of the electrostatic force is essentially governed by the surface potential and the range is proportional to the debye length. Debye length essentially depends on the electrolyte concentration. The 2Lo value gives the information about the special extension of the adsorbed polymer. The more the special extension the better the stability of the emulsion. In the case of polymers (PVA-vac) and polyelectrolytes (PAA), the decay length values are comparable to the radius of gyration of the polymer. Therefore, the decay length values tell us about the double layer length or the radius of gyration of the polymer at the ferrofluid interface. Example I: Electrostatic stabilization The initial emulsion is stabilized with SDS (anionic surfactant) and the droplet surface is negatively charged. The force measurement in the presence of SDS shows a clean electrostatic repulsive force profile due to the charges at the interface of the droplets and the force profiles very well follow the classical exponentially decay curves. Here, the 14 Debye length governs the range of repulsion and the magnitude of force depends on the surface potential. As the Debye length, depends on the SDS concentration (Cs), the emulsion becomes destabilized at high SDS or salt concentration due to small Debye lengths. Therefore, these observations clearly reveal that electrostatic stabilization approach fails to provide required stability to the colloidal formulation, when the electrolyte concentration is high. This shows the drawback of electrostatic stabilization, at high salt concentration. Example II: Steric stabilization The force profiles in the presence of adsorbed polymers (of PVA 40K, 1.15K and 155K) and weak polyelectrolytes (PAA 120K, 250K) decays exponentially with a decay length proportional to the radius of gyration. It has also been found that the decay length is insensitive to the bulk polymer concentration and the nature of liquid-liquid interface. The force profiles were clearly exponential with characteristic length close to the radius of gyration. Independently, we have also checked the Debye length variations for various surfactant concentrations (without any polymer). The observed values of decay length were in good agreement with the theoretical values. Using this approach, it has been found that the onset of repulsion is fixed by the molecular weight of the polymer used. There is no means to vary the onset of repulsion, once a polymer with a given molecular weight is adsorbed at the emulsion droplet. This shows the non- tunability of the onset and magnitude of repulsion under steric stabilization. Example III: Associative polymer stabilization (PVA 40K and SDS) Figure 1 shows the variation of force profiles in the presence of PVA of 40K at a concentration of 0.68 wt% for various sodium dodecyl sulphate (SDS) concentrations. The surfactant concentrations were varied from about CMC/50 to 2 CMC. The force profile without any SDS is also shown in the fig. 1 (open circles), which can be considered as the reference curve. The force profiles can be represented by a simple exponential function Where 'h' is the interdroplet spacing and 'X' is the decay length. The characteristic decay length without surfactant in this case was 7.6 nm, which is close to the hydrodynamic radius of gyration of the PVA. In the presence of very small amount of surfactant 15 (0.00026 M), the magnitude of force profile changed drastically, without much variation in the decay length. Here the decay length increases slightly from 7.6 to 8.4nm. However, the first interaction distance or onset of repulsion increases from 36 to 44 nm. We should emphasize that the emulsion, normally became unstable at this concentration, without the presence of polymer. However, in the presence of polymer, the system remains stable for a long time (over 10 months). As the concentration of SDS increases further, both the magnitude and the first interaction distance increase. The increase in the magnitude of force continues up to the CMC of SDS. On further increase in the surfactant concentration, the force profiles are not altered considerably. The above experimental results show that the onset of repulsion and the magnitude of force can be augmented by employing association of surfactant with polymers. The ferrofluid-based emulsion stabilized with PVA (0.68 %) alone is completely destabilized, after a period of 3 month [Example II]. Here, the ferrofluid oil droplets are phase separated from the continuous phase and are deposited at the bottom of the container. The ferrofluid emulsion stabilized with SDS at 3.02mM is partially destabilized, after a period of three month [Example I]. Microscopic observation shows many permanent aggregates in the emulsion. The emulsion stabilized by the new process (with PVA (0.5%) and SDS at CMC/10) is found to be perfectly stable, after a period of ten month. In all the above three cases, the polymer(PVA) average molecular weight was 40000. From Figure 1, it is evident that the spacing between the droplets (h) at a given force 2xl0"13 N, increases with increasing surfactant (SDS) concentration, providing better stability to the emulsion. From these results it is clear that the ferrofluid emulsions can be well stabilized by using following compositions: Component Weight percentage Possible Range Preferable range Emulsion 1-40 7-14 Aqueous phase 47- 98.9 84.2- 92.42 Block copolymer 0.001-5 0.5-1.0 Surfactant 0.05-8 0.08- 0.8 16 Example IV: Associative polymer stabilization (PVA 115K and SDS) Figure 2 shows the force profile for PVA of molecular weight 115K for various SDS concentrations. The observed results were similar to the previous case. The value of decay length in the absence of surfactant was 11.2 nm against the unperturbed coil diameter of 12nm. The observed variation was similar to those of 40K, except the fact that the range of increase in the onset of repulsion was much larger due to higher molecular weight of the polymer. From the experimental force profiles, the decay lengths were deduced. Decay length dictates the slope of the force profile and hence the range of repulsion. In the case of cationic and anionic surfactants, the decay length increases first, reaches a maximum value and then decreases. The total variation is about 5-6 nm in these cases, with respect to the unperturbed radius of gyration values. In the case of nonionic surfactant, the decay length is comparable to the unperturbed radius of gyration values. The measured Rg values, with and without surfactants, using viscometry and force experiments are in good agreement with each other. These results show that the decay length is insensitive to added electrolyte, which is an added advantage, especially when a product needs to have higher salt content. From Figure 2, it is evident that the spacing between the droplets (h) at a given force 2xl(r13 N increases with increasing surfactant (SDS) concentration, providing better stability to the emulsion. From these results it is clear that the ferrofluid emulsions can be well stabilized by using following compositions: Component Weight percentage Possible Range Preferable range Emulsion 1-40 7-14 Aqueous phase 47- 98.9 84.1-92.4 Block copolymer 0.001-5 0.5-1.0 Surfactant 0.05-8 0.1-0.9 Example V : Associative polymer stabilization (PVA 155K and SDS) Figure 3 shows the force profile for PVA of molecular weight 155K, for various SDS concentrations. The observed results were similar to the previous case. The value of decay length in the absence of surfactant was 16.5 nm against the unperturbed coil 17 diameter of 16nm. The observed variations in this case were also similar to those of 40K, except the fact that the range of increase in the onset of repulsion was much larger due to larger molecular weight of the polymer. From Figure 3, it is evident that the spacing between the droplets (h) at a given force 10"13 N increases with increasing surfactant (SDS) concentration, providing better stability to the emulsion. Fig.4 shows the force profiles, obtained at different time intervals, for ferrofluid emulsion stabilized with PVA 155K of 0.5% with 1.6mM SDS . It can be seen that the decay length and the onset of repulsion remains unchanged even after 10 months, indicating the long term stability during the storage period. Normally, the emulsions stabilized with conventional steric stabilization show hysterisis with time due to change in polymer conformation and desorption, however the emulsions stabilized with our new technique remains remarkably stable. Figure 4 shows that the spacing between the droplets of composition in Example V remains the same over a period of ten months. From these results it is clear that the ferrofluid emulsions can be well stabilized by using following compositions: Component Weight percentage Possible Range Preferable range Emulsion 1-40 7-14 Aqueous phase 47- 98.9 84.1-92 Block copolymer 0.001-5 0.9-1.1 Surfactant 0.05-8 0.1-0.8 Example VI: Associative polymer stabilization (PVA 155K and CTAB) \ Figure 5 shows the force profile for PVA of molecular weight 155K in associations with CTAB. The only difference in this case, compared to SDS is that the onset of repulsion begins at higher surfactant concentrations, close to the critical micellar concentration. From Figure 5, it is evident that the spacing between the droplets (h) at a given force 2xl0"13 N increases with increasing surfactant (CTAB) concentration, providing better stability to the emulsion. Figure 6 shows the force profiles, obtained at different time intervals, for ferrofluid emulsion stabilized with PVA 155K of 0.5% with 9 raM of CTAB . It can be seen that the decay length and the onset of repulsion remains unchanged even aftei 10 months, 18 indicating the long term stability during the storage/period. Normally, the emulsions stabilized with conventional steric stabilization show.hysterisis with time due to change in ^.t '«, '■' •': • -polymer conformation and desorption, however the emulsions stabilized with.our new technique remains remarkably stable. Figure 6 shows that the spacing between the droplets of composition in Example VI remains the same over a period of ten months. . From these results it is clear that the ferrofluid emulsions can be well stabilized by using following compositions: Component Weight percentage Possible Range Preferable range Emulsion 1-40 7-14 Aqueous phase 47- 98.9 84.88- 92.09 Block copolymer 0.001-5 0.9-1.1 Surfactant 0.05-8 0.01-0.02 Example VII: Associative polymer stabilization (TVA 155K with TTAB ) Fig.7 shows the force profiles, obtained at different time intervals, for ferrofluid emulsion stabilized with PVA 155K of 0.5% with 5.1mM TTAB . It can be seen that the decay length and the onset of repulsion remains unchanged even after 10 months, indicating the long term stability during the storage period. Normally, the emulsions stabilized with conventional steric stabilization show hysterisis with time due to change in polymer conformation and desorption, however the emulsions stabilized with our new technique remains remarkably stable. Figure 7 shows that the spacing between the droplets of composition in Example VII remains the same over a period often months. From these results it is clear that the ferrofluid emulsions can be well stabilized by using following compositions: Component Weight percentage Possible Range Preferable range Emulsion 1-40 7-14 Aqueous phase 47- 98.9 84.5- 92 Block copolymer 0.001-5 0.9-1.1 Surfactant 0.05-8 0.1-0.4 19 Example VIII: Associative polymer stabilization (PVA 155K with NP10 ) Fig. 8 shows the force profiles, obtained at different time intervals, for ferrofluid emulsion stabilized with PVA 155K of 0.5% with 5 mM NP10.' It can be seen that the decay length and the onset of repulsion remains unchanged even after 10 months, indicating the long term stability during the storage period. Figure 8 shows' that the spacing between the droplets of composition in Example VIII remains the same over a period of ten months. From these results it is clear that the ferrofluid emulsions can be well stabilized by using following compositions: Component Weight percentage Possible Range Preferable range Emulsion 1-40 7-14 Aqueous phase 47-98.9 83.9-92.0 Block copolymer 0.001-5 0.9-1.1 Surfactant 0.05-8.0 0.1-1.0 Main Advantages of the Invention The product Stabilized ferrofluid emulsions of the invention are stable and can be repeatedly used in the flux leakage probe for detecting and estimating defects in ferromagnetic materials for number of months or years. The new process removes some of the inherent limitations of electrostatic and steric stabilization methods. At the same time, it has several additional merits compared to the existing stabilization techniques. The new process enable us to control the magnitude and onset of repulsion by simply adding very low concentrations of surfactants, which would ultimately provide better long-term stability for the colloidal formulation. This new process eliminates the need for choosing polymers with higher molecular weights (or high radius of gyration) for increasing the magnitude and range of repulsion. This not only makes the procedure of stabilization easy but also makes it cost effective. The merits of the new process is summarized below: • The spatial extension of the double layer is not sensitive to electrolyte concentration • The decay length is insensitive to surfactant concentrations. 20 • Onset of repulsion can be tuned according to the requirement. • No need for polymers with very large molecular weights to increase the onset of repulsion • This procedure allows us to convert a low molecular weight neutral polymer into a high molecular weight polyelectrolyte or di-bloc polyelectrolyte. The new process is suitable for obtaining colloidal dispersions with long-term stability, where the onset and the magnitude of repulsions can be precisely controlled, without changing the molecular weight of the macromolecules. In other words, this process allows us to covert a low molecular weight neutral polymer into a high molecular weight polyelectrolyte or di-bloc polyelectrolyte. The stabilization technique is particularly ideal for stabilizing ferrofluid-based emulsions. Here, we exploit the associative behavior of polymer with surfactants. The association of polymer-surfactant complexes leads to dramatic increase in the onset of repulsive force due to the stretched brush like conformation of adsorbed polymers. The force profiles in the presence of associative polymer follow an exponential scaling with a characteristic decay length, comparable to the radius of gyration of the free polymer. This decay length is weakly dependent on the surfactant concentration. Since the surfactant-polymer binding is a continuous process, onset of repulsion between the colloidal particles can be controlled precisely by choosing the amount of surfactants. Non-ionic polymers with a wide variety of cationic and anionic surfactants can be used in the above process. 21 We Claim 1. A stabilized magnetic emulsion of oil-in-water type comprising (i) 1-40 wt. %, preferably 7-14 wt. % of a ferrofluid emulsion ; (ii) 47- 98.95 wt. %, preferably 82.5- 92.5 wt. % of an aqueous phase (iii) 0.001-5 wt. %, preferablyr0.01- 1.5 wt. % of an emulsifying agent selected from anionic, cationic and non ionic surfactant and mixtures.theREof; and (iv) 0.05-8.0 wt. %, preferably 0.5-2.0 wt. % of a block copolymer with hydrophobic and hydrophilic groups with a molecular weight ranging from 4000 to 4 00 000. 2. A stabilized magnetic emulsion of oil-in-water type as claimed in claim 1 wherein, said ferrofluid emulsion comprising 75-95 wt %, preferably 80-90 wt % of ferrofluid oil, 2-12 wt %, preferably 5-10 wt % of outer surfactant and 2-11 wt %, preferably 4-9.5 wt % of water. 3. A stabilized magnetic emulsion of oil-in-water type as claimed in any of claims 1 or 2 wherein, said ferrofluid Oil is a suspension of 30-60 wt. %, preferably 40-50 wt. % of magnetic particles selected from iron, nickel, cobalt, gamma-FezO3, magnetite and combinations thereof and the like, 0.5-3 wt. %, preferably 1-2 wt. % of absorbed inner surfactants selected from oleic acid, phosphoric acid and 37-69.5 wt. %, preferably 48-59 wt. % of a carrier selected from n-octane, cyclohexane, n-dodecane, n-tetradecane, n-hexadecane, n-octadecane, kerosene and the like. 4. A stabilized magnetic emulsion of oil-in-water type as claimed in any of claims 1 to 3 wherein the size of said magnetic particles varies from 5 to 12 nm, preferably from 7 to 10 nm 5. A stabilized ferrofluid emulsion of oil-in-water type as claimed in any of claims I to 4 wherein said'outen surfactant is selected from conventional anionic, cationic or non-ionic surfactants. 22 6. A stabilized magnetic emulsion of oil-in-water type as claimed in any of claims 1 to 5 wherein said anionic surfactant is selected from polyoxyethylene, alkylphenyl ether sulfates, polyoxyethylene styrenated phenyl ether sulfates, alkylphosphates, polyoxyethylene alkyl ether phosphates, polyoxyethylene alkylphenyl ether phosphates, fatty acid salts, alkylbenzene sulfonates, alkyl sulfonates, alkyl naphthalene sulfonates, alpha -olefin sulfonates, dialkyl sulfosuccinates, alpha -sulfonated fatty acid salts,N-acyl-N-methyllaurate, alkylsulfates, sulfated lipids, polyoxyethylene alkyl ether sulfates and naphthalene sulfonate formaldehyde condensates. 7. A stabilized magnetic emulsion of oil-in-water type as claimed any of claims 1 to 6 wherein said cationic surfactant is selected from alkyltrimethyl ammonium salts, primary to tertiary aliphatic amine salts, dialkyldimethyl ammonium salts, trialkylbenzyl ammonium salts, alkyl pyridinium salts, tetraalkyl ammonium salts, and polyethylene polyamine fatty acid amide salts. 8. A stabilized magnetic emulsion of oil-in-water type as claimed in any of claims 1 to 7 wherein said nonionic surfactant is selected from polyoxyethylene polyoxypropylene glycols, polyoxyethylene polyoxypropylene alkyl ethers, polyoxyethylene alkyl ethers, polyoxyethylene alkenyl ethers, polyoxyethylene alkylphenyl ethers, polyoxyethylene polystyrylphenyl ethers, polyhydric alcohol fatty acid partial esters, sorbitan fatty acid esters, glycerol fatty acid esters, deca-glycerol fatty acid esters, polyglycerol fatty acid esters, propylene glycol pentaerythritol fatty acid esters, polyoxyethylene sorbitan fatty acid esters, polyoxyethylene glycerol fatty acid esters, polyoxyethylene polyhydric alcohol fatty acid partial esters, polyoxyethylene fatty acid esters, polyglycerol fatty acid esters, polyoxyethylenated castor oil, fatty acid diethanolamides, polyoxyethylene alkylamines, triethanolamine fatty acid partial esters, trialkylamine oxides, and polyoxyalkylene group containing organopolysiloxanes. 9. A stabilized magnetic emulsion of oil-in-water type as claimed in any of claims 1 to 8 wherein said hydrophobic group in said block copolymer is selected from vinyl acetate, polysiloxane groups, polyfluro alkyl groups, legnine derivatives, poly propylene glycol derivatives, polybutylene oxide and the like. 23 10. A stabilized magnetic emulsion of oil-in-water type as claimed in any of claims 1 to 9 . wherein said hydrophilic group in said block copolymer is selected from poly vinyl alcohol, poly saccharide, starch, cellulose, polyurethane, polyetheiyne.oxide and the like. 11. A stabilized magnetic emulsion of oil-in-water type as claimed in any of claims 1 to 10 wherein the ratio of said hydrophobic group and said hydrophilic group is 5:95, preferably 10:90 and more preferably 20:80. 12. A stabilized magnetic emulsion of oil-in-water type as claimed in any of claims 1 to 11 wherein said block copolymer is polyvinyl alcohol and vinyl acetate 13. A process of preparing a stabilized magnetic emulsion of oil-in-water type as claimed in any of claims 1 to 12 comprising (i) preparing an emulsion by slowly adding oily phase into a premixed surfactant - water mixture and shearing it in an emulsifier to get a crude emulsion; (ii) diluting the said crude emulsion repetitively with water containing surfactant at CMC and fractionating the said crude emulsion to obtain monodispersed emulsion with droplet size in the range of 100-1000 nm. (iii) adding said block copolymer into the said crude emulsion and incubating at 25°C for atleast 72 hrs. (iv) adding further amount of same or different surfactant to the incubated crude emulsion, obtained at the end of step 3 and mixing them thoroughly, (v) incubating the emulsion obtained at the end of step (iv) at 25-35°C for a further period of atleast 1 hr to obtain a stabilized magnetic emulsion. 14.A process of preparing a stabilized magnetic emulsion of oil-in-water type as claimed in claim 13, wherein said shearing in step (i) is carried out at an rpm of 500 tolOOO for about 30 minutes. 15.A process of preparing a stabilized magnetic emulsion of oil-in-water type as claimed in claim 13, wherein the said further amount of same or different surfactant in step (iv) is 0.001 to 5 wt %; preferably 0.01 to 01.5 wt % of the said crude emulsion. 24 16. A stabilized magnetic emulsion of oil-in-water type and a process 'for preparing it .substantially as herein described in the text examples and drawings. Dated this 17th day of December 2002 S. MAJUMDAR S. MAJUMDAR & CO. Applicant' Agent

Full Text

FORM 2 THE PATENTS ACT 1970 (39 of 1970)

COMPLETE SPECIFICATION
( See section 10; rule 13).
TITLE
" Stabilized magnetic emulsion of ail-in-water and present of preparing the name"
APLICANT
Department of Atomic Energy Government of India, Department of the Govt, of India, having its office at Anushakthi Bhavan , Chathrapathy Shivaji Maharaj Marg, Mumbai, 400001, Maharashtra , India
The following specification describes the nature of the invention and the manner in which it is to be performed

19-12-2002

GRANTED

1

Field of Invention
The present invention relates to a stabilized magnetic emulsion and .a process of making it. The present invention particularly relates to magnetic emulsions known as ferrofluid emulsions, which are useful in non-destructive devices, sensors, optical filters etc
Background and Prior Art
Magnetic liquid, or ferrofluid oil is suspensions of ferromagnetic particles in a liquid carrier. Nanometer sized magnetite particles suspended in an organic liquid such as kerosene, octane. The particles are coated with a surfactant (called inner surfactant) such as oleic acid, phosphoric acid, to prevent flocculation of the particles of ferrofluid. Typically, the sizes of the particle are below 15 run. R E Rosenweig has described their preparation, properties and uses in an article in International Science and Technology, July 1966, pp. 45 -56. Preparations and usefulness of magnetic (ferrofluid) oil have also been described by R E Rosenweig in the book titled "Ferrodynamics", 1985, Cambridge University Press, N Y.
A direct ferrofluid emulsion consists of ferrofluid oil, a water-soluble surfactant (called outer surfactant) and a continuous phase of water. Here, the oil droplets are dispersed in a continuous phase of water. Typically, the size of the droplets is of the order of 100 run to a few microns.
Preparation of a typical ferrofluid emulsion has been described by J Philip et al., in
Measurement Science and Technology Volume 10, Year 1999, pp N71-N75, as follows:
i. Mix slowly sodium dodecyl sulphate (SDS)(5 g) and water (5 g);
ii. Add ferrofluid oil (90 g) to the above solution to get w/o emulsion with very large
droplets of diameter 10 (µm or more; iii. Then mix it thoroughly in a colloid mixer to obtain o/w emulsion with droplet
diameter in the range of 0.1 to 1 µm; iv. Dilute it further with water to get a final SDS level in the emulsion 2.3 g 1"'.
Such a ferrofluid is an oil-in-water emulsion, which has been employed for detecting defects in ferromagnetic materials and components described inund. Pat. Nos. 186620 & /186574}by a method called magnetic flux leakage probe.
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In these methods, monodispersed ferrofluid is confined between two thin transparent glass slides and a white light source for illumination. It has been shown that by employing ferrofluid droplets of suitable size and surfactant concentration, one can qualitatively identify the region where the defect is located in the test specimen by visually observing a color change in the ferrofluid cell, in the vicinity of a crack or defect in the test specimen. The second patent-(Ind. 186620) reveals a technique to quantify the defect characterization based on a spectrograph-based system, which precisely computes the Bragg peak wavelength that is related to the crack size and position.
The ferrofluid emulsions employed in the optical probes disclosed in the above patents, often deteriorates after prolonged use, under harsh environments. As a result, the emulsion, sometimes, is destabilized after a few months of use, and it becomes necessary to replace it with fresh emulsion at regular intervals of time. Emulsions used in those probes were stabilized either electrostatically of sterically but both these stabilization techniques were not very effective for long term stability. There are no such stabilized systems (oil-in-water type of emulsion with solid magnetic particles inside the oily phase) described in the prior art. Other prior art disclosing stabilization of other emulsions are:
(US patent 6,074,470/ discloses a stable aqueous silane emulsion with constant particle size. The emulsion comprises a continuous water phase, a discontinuous silane phase, and an emulsifier system.
D. H. Napper, has reviewed the subject of stabilization of emulsions in general, in 1987, in his book titled Polymeric Stabilization of Colloidal Dispersions; Marcel Dekker: New York, 1987. There are also a few other reviews on polymeric stabilizations, e.g.; Th. Tadors 1988 Polymers in colloidal systems, Elsevier: Amsterdam etc. J N Isrelachvili, 1985 Intermodular and Surface Forces, San Diego: Academic Press. Steric stabilization techniques are used in numerous industrial applications such as paints, toners, emulsions, cosmetics, pharmaceuticals, processed food, lubricants etc. For example((US patent 6,346,256 discloses an oil/water/oil emulsion stabilized with at least one partially or completely cross-linked organopolysiloxane elastomer having at least one polyoxyethylenated and/or polyoxypropylenated chain. Some of the other example for steric stabilizations, methods.-employed in various formulations, ^disclosed in US patents\ are 5,153,233, 5,438,088, 6,346,600, 5,507,804 etc.
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'■■!..* -

In the case of electrostatic stabilization, ionic/ nonionic ^surfactants are employed. The electrostatically stabilized colloids often coagulate wheh, the .ionic'-strength of the. medium is increased sufficiently high, due to the reduction in the, spatial, extension of electrical double layers. For example, an ionic strength higher than O.OOIM, 'corresponds to a length of about lOnm for a 1:1 electrolyte that can lead to van der Waals attraction in the dispersion. This is the range where electrostatic stabilization often fails. For certain emulsions electro-steric stabilizations have been reported in which polyelectrolytes have been employed, but there is no relevant prior art that provides a systematic method to improve stability of such emulsions, there is no guideline to impart long-range repulsion between the colloidal particles; particularly water-in-oil emulsions of the ferrofluid described above.
Object
The principal object of the invention is to obtain a well-stabilized ferrofluid emulsion
[oil-in-water] that can be reused a number of times in optical probes especially those described in aforesaid Indian Patent specification Nos.I86620 & 186574.
Summary of the Invention
Accordingly, the present invention provides a stabilized magnetic emulsion of oil-in-water type comprising:
(i) 1-40 wt. %, preferably 7-14 wt. % of a ferrofluid emulsion ; (ii) 47- 98.95 wt. %, preferably 82.5- 92.5 wt. % of an aqueous phase (iii) 0.001-5 wt. %, preferably 0.01- 1.5 wt. % of an emulsifying agent selected from anionic, cationic and non ionic surfactant and mixtures thereof; and (iv) 0.05-8.0 wt. %, preferably 0.5-2.0 wt. % of a block copolymer with hydrophobic and hydrophilic groups with a molecular weight ranging from 4000 to 4 00 000. and a process of preparing said stabilized magnetic emulsion of oil-in-water type comprising
(i) preparing an emulsion by slowly adding oily phase into a premixed
surfactant - water mixture and shearing it in an emulsifier to get a crude
emulsion; (ii) diluting the said crude emulsion repetitively with water containing surfactant
at CMC and fractionating the said crude emulsion to obtain monodispersed
emulsion with droplet size in the range of 100-1000 nm.
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(iii) adding said block copolymer into the said .crude emulsion and incubating at
25°C for atleast 72 hrs. (iv) adding further amount of same or different surfactant to the incubated crude
emulsion, obtained at the end of step 3 and mixing them thoroughly, (v) incubating the emulsion obtained at the end of step (iv) at 25-3~5°C for a further
period of atleast 1 hr to obtain a stabilized magnetic emulsion.
It is preferable to carry out the shearing in step (i) at rpm of 500 to 1000 for about 30 minutes and the further amount of surfactant in step (iv) is 0.001 to 5 wt %; preferably 0.01 to 01.5 wt% of the said crude emulsion.
Detailed description of the Invention:
The size of said magnetic particles inside the stabilized emulsion of the present invention varies from 5-15 nm, preferably it is in the range of 7-10 nm. The inner surfactant used is chosen from oleic acid, phosphoric acid etc. The carrier used is chosen from oils such as octane, cyclohexane, kerosene.
The surfactant is chosen from anionic, cationic or non-ionic types, which are well known in the field.
The anionic surfactant are chosen from surfactants such as polyoxyethylene, alkylphenyl ether sulfates, polyoxyethylene styrenated phenyl ether sulfates, alkylphosphates, polyoxyethylene alkyl ether phosphates, polyoxyethylene alkylphenyl ether phosphates, fatty acid salts, alkylbenzene sulfonates, alkyl sulfonates, alkyl naphthalene sulfonates, alpha -olefin sulfonates, dialkyl sulfosuccinates, alpha -sulfonated fatty acid salts, N-acyl-N-methyllaurate, alkylsulfates (e.g. SDS), sulfated lipids, polyoxyethylene alkyl ether sulfates and naphthalene sulfonate formaldehyde condensates.
The cationic surfactant^ is chosen from alkyltrimethyl ammonium salts (e.g. CTAB, TTAB), primary to tertiary aliphatic amine salts, dialkyldimethyl ammonium salts, trialkylbenzyl ammonium salts, alkyl pyridinium salts, tetraalkyl ammonium salts, and polyethylene polyamine fatty acid amide salts.
The nonionic surfactant is such as polyoxyethylene polyoxypropylene glycols, polyoxyethylene polyoxypropylene alkyl ethers, polyoxyethylene alkyl ethers, polyoxyethylene alkenyl ethers, polyoxyethylene alkylphenyl ethers (e.g. NP10),
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polyoxyethylene polystyrylphenyl ethers, polyhydric alcohol fatty acid partial' esters, sorbitan fatty acid esters, glycerol fatty acid esters, deca-glycerol fatty acid esters,, polyglycerol fatty acid esters, propylene glycol pentaerythritol fatty acid esters, polyoxyethylene sorbitan fatty acid esters, polyoxyethylene glycerol fatty acid esters, polyoxyethylene polyhydric alcohol fatty acid partial esters, polyoxyethylene fatty acid esters, polyglycerol fatty acid esters, polyoxyethylenated castor oil, fatty acid diethanolamides, polyoxyethylene alkylamines, triethanolamine fatty acid partial esters, trialkylamine oxides, and polyoxyalkylene group containing organopolysiloxanes.
A block copolymer with a hydrophobic group such as vinyl acetate, polysiloxane groups, polyfluro alkyl groups, legnine derivatives, poly propylene glycol derivatives, polybutylene oxide etc. and a hydrophilic group such as poly vinyl alcohol, poly saccharide, starch, cellulose, polyurethane, polyethelyne oxide etc. with a molecular weight ranging from 4000 to 4 00 000. The ratio of hydrophobic and hydrophilic group can range from 5:95, preferably from 10:90 and more preferably in the range of 20:80.
The block copolymer used is preferably, polyvinyl alcohol (88 wt%) with vinyl acetate (12 wt%). The crude emulsion obtained at the end of step 1 is fractionated* to obtain a monodispersed emulsion with a droplet size in the range of 100 - 1000 nm. Then the steps (ii) to (viii) are repeated to obtain a stabilized monodispered emulsion.
*Fractionation is a process to obtain monodispersed emulsion droplets. When surfactant concentration is above a critical micellar concentration, the emulsions droplets begin to flocculate or cream due to depletion flocculation induced by the non-adsorbed surfactant. In an emulsion containing droplets of the order of hundreds of nanometer, the non-adsorbed surfactant forms the aggregates of the order of a few nanometers. When the emulsion droplets approach closer the thickness of the continuous phase film becomes smaller and smaller and when it is smaller than the micelle diameter micelles are expelled from the thin film. So the thin film region experiences a large activity of the solvent than the surroundings and an osmotic pressure develops pushing the droplets closer. On addition of surfactant to a critical concentration to a typical polydispersed O/W emulsion, the dense phase of aggregated oil droplets separates from a dilute phase of free droplets. At the flocculation threshold the dense phase contains most of the bigger droplets and the dilute phase mainly smaller ones. First step the dilute phase is separated and the dense
6

phase is again diluted with more surfactant. The above process is repeated several times to obtain monodisperesed emulsion and this process is well known in the field.
For the purpose of this invention, a 'stable' emulsion is defined as (1) an emulsion having no phase separation and no formation of sediment or a layer of cream, or (2) if formation of sediment or a layer of cream does occur, the emulsion can be obtained by simple shaking or stirring with no loss of effects. The stability of such emulsions prepared by the above process is tested by force apparatus, microscopic and macroscopic observations at regular intervals of time. An optical phase contrast microscope (M/s Leica DM IRM) equipped with a digital camera (JVC) and imaging software (Leica) has been used for observing the emulsion droplets. Force experiments have been performed using a home built force apparatus, which allow measurement of forces between individual emulsion droplets. These methods are described in our co-pending Ind. Pat. Application. No. 501/Mum/02.
Examples:
The invention will now be illustrated with the help of a few examples. The examples are
by way of illustration only and in no way restrict the scope of the invention. Examples I
and II are not of the present invention; Examples HI - VTA are of the present invention.
Drawings
Flow Chart 1 : A flowchart of process of the present invention in general and that used in
the Examples III-VIII. The processes of Examples I and II are experiments on prior art,
using either surfactant or polymer. The above examples are used for comparing the
stability of the samples that are prepared using the newly invented process, with prior art
processes.
Variation of force (N) Vs inter-droplet spacing (ran), in the presence of surfactant and
polymer systems are shown in
Fig 1: for PVA of 40K (0.68wt%) for different SDS concentrations ( 0.0046wt% to
1.152 wt%). (Based on the data given in Table 1 and Example IIII)
Fig 2 :for PVA of 115K (0.49wt%) for different SDS concentrations ( 0.0034wt% to
0.28 wt%). (Based on the data given in Table 1 and Example IV)
Fig 3 :for PVA of 155K (0.45wt%) for different SDS concentrations ( 0.0033 wt% to
0.126 wt%). (Based on the data given in Table 1 and Example V)
Fig 4 : for PVA of 155K (0.45wt%) for different SDS concentrations (1.6mM up to 10
Months). (Based on the data given in Table 1 and Example V)

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Fig 5 : for PVA of 155K (0.43wt%) for different CTAB concentrations ( 0.0002 wt% to
0.0245wt%). (Based on the data given in Table 1 and Example VI)
Fig 6 : for PVA of 155K (0.5wt%) for CTAB 9mM up to 10 months storage.
(Based on the data given in Table 1 and Example VI)
Fig 7 : for PVA of 155K (0.5wt%) for TTAB 5. ImM up'to 10 months storage.
(Based on the data given in Table 1 and Example VTI).
Fig 8 : for PVA of 155K (0.5wt%) for NP10 5.0 mM up to 10 months storage.
(Based on the data given in Table 1 and Example VTH).
Materials used for the examples :
Ferrofluid emulsion
Ferrofluid emulsion was prepared by mixing 5 part of surfactant with 5 parts of water until the surfactant was completely mixed with the water. The outer surfactant used in the experiment was SDS. The ratio of SDS, water and ferrofluid oil was 5:5:90. Then 90 parts of the octane based ferrofluid oil is added to the above surfactant-water mixture. The resulting mixture was stirred at 500 RPM with a 1-inch diameter blade for 20 minutes.
Aqueous phase : Water -triply distilled. Surfactant
The anionic surfactant: sodium dodecyl sulphate (C12H25-SO4 Na), hereafter described as SDS. The cationic surfactants: -Cetyltrimethyl ammonium bromide (CTAB), and Tetradecyltrimethyl ammonium bromide (TTAB). The nonionic surfactant : nonyl phenol ethoxylate (NP10). SDS, CTAB.TTAB, NP10 etc. obtained from Sigma, USA. The purity of all the surfactants was about 99.9 %.
Polymer: The polymer used in these experiments was a statistical copolymer of vinyl alcohol (CH2CHOH -88 wt%.) and vinyl acetate (CH (OCOCH3)-12 wt%), which is randomly distributed along the polymer chain, of three average molecular weights of 40000, 115000 and 155000 (here after referred as PVA 40K, 115K and 155K respectively). The Polyelectrolyte used in our experiment was polyacrylic acid (PAA). PVA 40K, 115K and 155K; and the polymers were obtained from Aldrich, USA.
Weak Polyelectrolytes : Polyacrylic acid (PAA) 120K, 250K (Aldrich, USA)
Stabilized Ferrofluid Emulsion Composition:
The composition of the ferrofluid oil, used in all the examples is the same (i.e. 45 wt% of 8 run sized Fe304 coated with oleic acid (less than 1 wt%) in 54 wt% of octane).

8
The basic composition of the un-stabilized ferrofluid emulsion is the same in all the cases
(i.e. ferrofluid oil-in-water emulsion 9.8 wt%, aqueous phase 90 wt% and surfactant
(SDS) 0.004 wt%.
The compositions of emulsions prepared in these examples are given in Table 1.
Table 1: Ferrofluid Emulsion Compositions
Example 1:Surfactant Only (SDS)

Surf. mM Surf. (wt%) PVA (wt%) FF (wt%) water (wt%) debye length (nm) 2Lo(nm)
0.571 - 0.016 0 9.8 90.18 12.9 64
0.756 0.021 0 9.8 90.179 10.9 56
1 0.028 0 9.8 90.172 9.3 52
1.51 0.043 0 9.8 90.15 7.8 46
3.02 0.086 0 9.$ $0.11| 6.2 39
7.56 0.217 0 9.8 89.98 2.85 22
Example 2: Polymer Only-PVA40K

Surf. mM Surf. (wt%) PVA-vac (wt%) FF (wt%) water (wt%) debye length (nm) 2Lo(nm)
0 0 0.68 10 89.32 5.9 29.5
o; 0 0.5 1o; 89.50 111.7 62
0 0 0.52 10 89.48 13.4 73
Example 3:40K+ SDS

Surf. mM Surf. (wt%) PVA-vac (wt%) FF (wt%) water (wt%) debye length (nm) 2Lo(nm)
, 0 0 0.68 11 88.32 5.9 29.5
16 0.00460 0.68 11 87.85 5.81 33
0.26 0.007 0.68 11 88.31 6.15 36.5
0.8 0.023 0.68 11 88.29 6.9 44
1.6 0.046 0.68 11 88.27 7.1 56
3.2 0.092 0.68 11 88.22 7.8 66
8 0.230 0.68 11 88.08 7.2 72
24 0.691 0.68 11 87.62 6.6 74
40 1.152 0.68 11 87.16 6.6 75
Example 4:115K+SDS

Surf. mM Surf. (wt%) PVA-vac (wt%) FF (wt%) water (wt%) debye length (nm) 2Lo(nm)
0 0 0.49 9.6 89.91 11.57 57
0.12 0.0034 0.49 9.6 89.90 11.8 64
0.236 0.0067 0.49 9.6 89.90 11.8 66
0.386 0.0111 0.49 9.6 89.89 12.1 67.5
0.81 0.0233 0.49 9.6 89.88 14.16 80
2.4 0.0691 0.49 9.6 89.84 14 111
3.94 0.1134 0.4$ 96 89.79, 13.6 125
8.1 0.2332 0.49 9.6 89.67 12.8 142
9.8 0.2822 0.49 9.6 89.62 12.3 160
9
Example 5:155K+ SDS

Surf. mM Surf. (wt%) PVA-vac (wt%) FF
(wt%) water (wt%) debye length (nm) 2Lo(nm)
0 0 0.45 11 88.55 13.24 73
0.118 0.0033 0.45 11 88.54 10.63 69
0.29 0.0083 0.45 11 88.54 13.8 77
0.53 0.0152 0.45 11 88.53 115.9; 91!
0.8 0.0230 0.45 11 88.52 15.9 106
1.6 0.0460 0.45 11 88.50 15.38 133
4.4 0.1267 0.45 11 88.42 13.47 158
Example 6- 155K+CTAB

Surf. mM Surf. (wt%) PVA-vac (wt%) FF (wt%) water (wt%) debye lenqth (nm) 2Lo(nm)
0 0 0.43 10 89.57 12.418 60
0.06 0.0002 0.43 10 89.56 9.99 60
0.225 0.0008 0.43 10 89.56 9.951 60
0.68 0.0024 0.43 10 89.56 11.186 60
0.9 0.0032 0.43 10 89.56 11.148 62
1.35 0.0049 0.43 10 89.56 12.225 65
1.8 0.0065 0.43 10 89.56 14.327 75
2.25 0.0081 0.43 10 89.56 15.442 95
2.7 0.0098 0.43 10 89.56 16.077 105
3.15 0.0114 0.43 10 89.55 15.535 113
4.05 0.0147 0.43. 10 89.55 15.385 125
4.95 0.0180 0.43 10 89.55 14.286 135
5.85 0.0212 0.43 10 89.54 14.43 145
6.75 0.0245 0.43 10 89.54 14.124 151
Example 7- 155K+TTAB

Surf. mM Surf. (wt%) PVA-vac (wt%) FF (wt%) water (wt%) debye length (nm) 2Lo(nm)
0 0 0.5 12 87.5 53
.0875 0.0029 0.5 12 87.49 9.505 55
0.175 0.0058 0.5 12 87.49 9.7182 60
0.35 0.0117 0.5 12 87.48 9.5511 61
1.4 0.0470 0.5 12 87.45 11.601 62
2.1 0.0706 0.5 12 87.42 13.089 70
2.8 0.0941 0.5 12 87.40 14.327 85
3.5 0.1177 0.5 12 87.38 15.198 103
4.375 0.1471 0.5 12 87.35 15.625 117
5.25 0.1766 0.5 12 87.32 15.06 130
6.125 0.2060 0.5 12 87.29 14.514 135
7.0 0.2354 0.5 12 87.26 13.69 142
8.75 0.2943 0.5 12 87.20 13.1 152
10
Example8- 155K-NP10

Surf. mM Surf. (wt%) PVA -Vac (wt%) FF (wt%) water (wt%) debye length (nm) 2Lo(nm)
0.0000125 0.000826 0.5 12 87.49917 10.6383 .55
0.000025 0.001652 0.5 12 87.49835 10 56
0.00005 0.003304 0.5 12 87.4967 10.10101 57
0.00015 0.009912 0.5 12 87.49009 10.52632 60
0.00025 0.01652 0.5 12 87.48348 10.41667 63
0.0005 0.03304 0.5 12 87.46696 10.20408 66
0.0012 0.079296 0.5 12 87.4207 10.23541 70
0.0025 0.1652 0.5 12 87.3348 10.46025 70
0.005 0.3304 0.5 12 87.1696 10.4 70.2
0.0075 0.4956 0.5 12 87.0044 10.3 69.5
The compositions marked in bold letters in each tables were further studied for their shelf life by actual storage and the results are shown in table 2.
Process of Manufacture of Stabilized Ferrofluid Emulsion.
The various compositions of Examples I-VII shown in Table 1 were prepared by the process described as per flow chart 1.
Ferrofluid emulsion was prepared by mixing 10 part of surfactant with 10 parts of water until the surfactant was completely mixed with water. The surfactant used in the Examples I -V was SDS. In Example VI and VHI it was CTAB , TTAB and NP10 respectively. The ferrofluid oil contains 10% of Fe304 grains with average grain size of 8nm. The resulting mixture was stirred at 500 RPM, with a 1-inch diameter blade for 30 minutes, using an emulsifier [REMI-RQ122, India). After 30 minutes, the mixture was diluted with water. The resulting mixture was poured into a cylindrical measuring jar. After this process a crude emulsion with wide size distribution was obtained, which was size selected using the fractionation approach mentioned earlier. Then the surfactant concentration of the size-selected emulsion was fixed at cmc/40 (below this value the emulsion becomes destabilized) by dilution with triply distilled water. The required quantity of macromoleeules (PVA) was introduced into the colloidal system and stirred until the macromoleeules were mixed properly with colloidal droplets. The whole system was incubated for at least 72 hrs. (in Example 1 polymer was not added). After reaching equilibrium, the surfactants of required values were add and the system was well stirred. The colloidal suspension was kept for a few hours [maximum 2 hours] to reach the equilibrium conditions. The system can then be used for various applications.

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Stabilization Studies :
The stabilization of the ferrofluid emulsions prepared in the above Examples I-III with
compositions as given in Table 1, were studied by the force measurement procedure described in the Indian Patent Application No. 501/MUM/02.
The system is later used for our experiments to check the stability tests using microscopic, macroscopic approaches. The optimum value of the macromolecule and the surfactant concentration have been measured quantitatively using our force measurement apparatus, which enabled us the estimation of onset of repulsion and the magnitude of force for a given ratio of macromolecule and surfactant concentration. The exact quality of the formulations has also been tested by other means such as turbidity or macroscopic phase separation as a function of time. The results are given in Table 2. These results show that the stability of emulsions stabilized using the above approach was far superior compared to those stabilized electro or steric (prior art) methods.
Stability as Shelf life studies
A representative sample of each Examples I-VTfl with compositions as shown in Table 2 have been prepared and kept in vials and the stability of emulsions was observed at various time intervals. The stability test results are tabulated in Table 2
12

Exa¬mple Sample Time (month) Microscopy Macroscopic Force Apparatus (Magnetic field induced chaining)
I. Surfactant stabilized with 3.02 mM SDS 1 No flocs* Single phase# stable

3 Few flocs Almost single unstable

5 IA** Two phase ## -

8 IA Two phase -

10 IA Two phase -
II PVA-Vac stabilized with 40K, at 0.5% 1 No flocs Single phase stable

3 No flocs Single phase stable

5 IA Two phase -

8 IA Two phase -

10 IA Two phase -
III PVA-Vac (40K, 0.68%) and SDS (3.2 mM) 1 No flocs Single phase stable

3 No flocs Single phase stable

5 No flocs Single phase stable

8 No flocs Single phase stable

10 No flocs Single phase stable
IV PVA-Vac(115K, 0.68%) and SDS (3.94mM) 1 No flocs Single phase stable

3 No flocs Single phase stable

5 No flocs Single phase stable

8 No flocs Single phase stable

10 No flocs Single phase stable
V PVA-Vac (155K, 0.45%) and SDS (4.4 mM) 1 No flocs Single phase stable

3 No flocs Single phase stable

5 No flocs Single phase stable

8 No flocs Single phase stable

10 No flocs Single phase- stable
VI PVA-Vac (155K, 0.43%) and CTAB (4.05 mM) 1 No flocs Single phase stable

3 No flocs Single phase stable

5 No flocs Single phase stable

8 No flocs Single phase stable

10 No flocs Single phase stable
VII PVA-Vac(155K, 0.5%) and TTAB (8.7 mM) 1 No flocs Single phase stable

3 No flocs Single phase stable

5 No flocs Single phase stable

8 No flocs Single phase stable

10 No flocs Single phase stable
VIII PVA-Vac(155K, 0.5%) and NP10 (15 mM) 1 No flocs Single phase stable

3 No flocs Single phase stable

5 No flocs Single phase stable

8 No flocs Single phase stable

10 No flocs Single phase stable
*No Floes, means no particle aggregates and the emulsion is perfectly stable.
**IA means the droplets form irreversible aggregates and the emulsion becomes completely destabilized.
#Single phase means the emulsion is perfectly stable
##Two phase means oil and water phases separate and the system becomes destabilized.

13
Our observations on the results of these tests in respect of each of these examples are
given below: '
Details of the force experimental technique and the interpretation of force results with respect to the stability of the emulsion is briefly discussed below: As the ferrofluid droplets are super paramagnetic in nature, an applied field induces a magnetic dipole in each drop, causing them to form chains. The magnitude of the induced dipole is controlled by the strength of the applied field. At low concentrations, one droplet thick chains are well separated and oriented along the field direction. Due to the presence of the one-dimensional ordered structure, a Bragg peak can be observed, from which the inter-droplet separation (h) can be estimated precisely, using a spectrograph. The condition for forming a linear chain is that the repulsive force between the droplets must exactly balance the attractive force between the droplets induced by the applied magnetic field. The sensitivity in the distance measurement, in our experimental set up, was 0.1 nm. The range of force that can be probed using this technique is 10"1 N to 10",13N.
From the force profiles, we deduce three parameters- A, from the slope, the first interaction length or onset of repulsion (2Lo) defined as the distance at which the magnitude of force is 2xl0"13 N and the magnitude of force (k). In the case of surfactant stabilized colloids, the force profiles have been found to be exponentially decaying, where the magnitude (k) of the electrostatic force is essentially governed by the surface potential and the range is proportional to the debye length. Debye length essentially depends on the electrolyte concentration. The 2Lo value gives the information about the special extension of the adsorbed polymer. The more the special extension the better the stability of the emulsion. In the case of polymers (PVA-vac) and polyelectrolytes (PAA), the decay length values are comparable to the radius of gyration of the polymer. Therefore, the decay length values tell us about the double layer length or the radius of gyration of the polymer at the ferrofluid interface.
Example I: Electrostatic stabilization
The initial emulsion is stabilized with SDS (anionic surfactant) and the droplet surface is negatively charged. The force measurement in the presence of SDS shows a clean electrostatic repulsive force profile due to the charges at the interface of the droplets and the force profiles very well follow the classical exponentially decay curves. Here, the

14
Debye length governs the range of repulsion and the magnitude of force depends on the surface potential. As the Debye length, depends on the SDS concentration (Cs), the emulsion becomes destabilized at high SDS or salt concentration due to small Debye lengths. Therefore, these observations clearly reveal that electrostatic stabilization approach fails to provide required stability to the colloidal formulation, when the electrolyte concentration is high. This shows the drawback of electrostatic stabilization, at high salt concentration.
Example II: Steric stabilization
The force profiles in the presence of adsorbed polymers (of PVA 40K, 1.15K and 155K) and weak polyelectrolytes (PAA 120K, 250K) decays exponentially with a decay length proportional to the radius of gyration. It has also been found that the decay length is insensitive to the bulk polymer concentration and the nature of liquid-liquid interface. The force profiles were clearly exponential with characteristic length close to the radius of gyration. Independently, we have also checked the Debye length variations for various surfactant concentrations (without any polymer). The observed values of decay length were in good agreement with the theoretical values. Using this approach, it has been found that the onset of repulsion is fixed by the molecular weight of the polymer used. There is no means to vary the onset of repulsion, once a polymer with a given molecular weight is adsorbed at the emulsion droplet. This shows the non- tunability of the onset and magnitude of repulsion under steric stabilization.
Example III: Associative polymer stabilization (PVA 40K and SDS)
Figure 1 shows the variation of force profiles in the presence of PVA of 40K at a concentration of 0.68 wt% for various sodium dodecyl sulphate (SDS) concentrations. The surfactant concentrations were varied from about CMC/50 to 2 CMC. The force profile without any SDS is also shown in the fig. 1 (open circles), which can be considered as the reference curve. The force profiles can be represented by a simple exponential function

Where 'h' is the interdroplet spacing and 'X' is the decay length. The characteristic decay length without surfactant in this case was 7.6 nm, which is close to the hydrodynamic radius of gyration of the PVA. In the presence of very small amount of surfactant

15
(0.00026 M), the magnitude of force profile changed drastically, without much variation in the decay length. Here the decay length increases slightly from 7.6 to 8.4nm. However, the first interaction distance or onset of repulsion increases from 36 to 44 nm. We should emphasize that the emulsion, normally became unstable at this concentration, without the presence of polymer. However, in the presence of polymer, the system remains stable for a long time (over 10 months). As the concentration of SDS increases further, both the magnitude and the first interaction distance increase. The increase in the magnitude of force continues up to the CMC of SDS. On further increase in the surfactant concentration, the force profiles are not altered considerably. The above experimental results show that the onset of repulsion and the magnitude of force can be augmented by employing association of surfactant with polymers.
The ferrofluid-based emulsion stabilized with PVA (0.68 %) alone is completely destabilized, after a period of 3 month [Example II]. Here, the ferrofluid oil droplets are phase separated from the continuous phase and are deposited at the bottom of the container. The ferrofluid emulsion stabilized with SDS at 3.02mM is partially destabilized, after a period of three month [Example I]. Microscopic observation shows many permanent aggregates in the emulsion. The emulsion stabilized by the new process (with PVA (0.5%) and SDS at CMC/10) is found to be perfectly stable, after a period of ten month. In all the above three cases, the polymer(PVA) average molecular weight was 40000.
From Figure 1, it is evident that the spacing between the droplets (h) at a given force 2xl0"13 N, increases with increasing surfactant (SDS) concentration, providing better stability to the emulsion. From these results it is clear that the ferrofluid emulsions can be well stabilized by using following compositions:

Component Weight percentage

Possible Range Preferable range
Emulsion 1-40 7-14
Aqueous phase 47- 98.9 84.2- 92.42
Block copolymer 0.001-5 0.5-1.0
Surfactant 0.05-8 0.08- 0.8
16
Example IV: Associative polymer stabilization (PVA 115K and SDS)
Figure 2 shows the force profile for PVA of molecular weight 115K for various SDS concentrations. The observed results were similar to the previous case. The value of decay length in the absence of surfactant was 11.2 nm against the unperturbed coil diameter of 12nm. The observed variation was similar to those of 40K, except the fact that the range of increase in the onset of repulsion was much larger due to higher molecular weight of the polymer.
From the experimental force profiles, the decay lengths were deduced. Decay length dictates the slope of the force profile and hence the range of repulsion. In the case of cationic and anionic surfactants, the decay length increases first, reaches a maximum value and then decreases. The total variation is about 5-6 nm in these cases, with respect to the unperturbed radius of gyration values. In the case of nonionic surfactant, the decay length is comparable to the unperturbed radius of gyration values. The measured Rg values, with and without surfactants, using viscometry and force experiments are in good agreement with each other. These results show that the decay length is insensitive to added electrolyte, which is an added advantage, especially when a product needs to have higher salt content.
From Figure 2, it is evident that the spacing between the droplets (h) at a given force 2xl(r13 N increases with increasing surfactant (SDS) concentration, providing better stability to the emulsion. From these results it is clear that the ferrofluid emulsions can be well stabilized by using following compositions:

Component Weight percentage

Possible Range Preferable range
Emulsion 1-40 7-14
Aqueous phase 47- 98.9 84.1-92.4
Block copolymer 0.001-5 0.5-1.0
Surfactant 0.05-8 0.1-0.9
Example V : Associative polymer stabilization (PVA 155K and SDS)
Figure 3 shows the force profile for PVA of molecular weight 155K, for various SDS concentrations. The observed results were similar to the previous case. The value of decay length in the absence of surfactant was 16.5 nm against the unperturbed coil
17
diameter of 16nm. The observed variations in this case were also similar to those of 40K, except the fact that the range of increase in the onset of repulsion was much larger due to larger molecular weight of the polymer. From Figure 3, it is evident that the spacing between the droplets (h) at a given force 10"13 N increases with increasing surfactant (SDS) concentration, providing better stability to the emulsion. Fig.4 shows the force profiles, obtained at different time intervals, for ferrofluid emulsion stabilized with PVA 155K of 0.5% with 1.6mM SDS . It can be seen that the decay length and the onset of repulsion remains unchanged even after 10 months, indicating the long term stability during the storage period. Normally, the emulsions stabilized with conventional steric stabilization show hysterisis with time due to change in polymer conformation and desorption, however the emulsions stabilized with our new technique remains remarkably stable. Figure 4 shows that the spacing between the droplets of composition in Example V remains the same over a period of ten months. From these results it is clear that the ferrofluid emulsions can be well stabilized by using following compositions:

Component Weight percentage

Possible Range Preferable range
Emulsion 1-40 7-14
Aqueous phase 47- 98.9 84.1-92
Block copolymer 0.001-5 0.9-1.1
Surfactant 0.05-8 0.1-0.8
Example VI: Associative polymer stabilization (PVA 155K and CTAB)
\ Figure 5 shows the force profile for PVA of molecular weight 155K in associations with
CTAB. The only difference in this case, compared to SDS is that the onset of repulsion
begins at higher surfactant concentrations, close to the critical micellar concentration.
From Figure 5, it is evident that the spacing between the droplets (h) at a given force
2xl0"13 N increases with increasing surfactant (CTAB) concentration, providing better
stability to the emulsion.
Figure 6 shows the force profiles, obtained at different time intervals, for ferrofluid emulsion stabilized with PVA 155K of 0.5% with 9 raM of CTAB . It can be seen that the decay length and the onset of repulsion remains unchanged even aftei 10 months,

18
indicating the long term stability during the storage/period. Normally, the emulsions
stabilized with conventional steric stabilization show.hysterisis with time due to change in
^.t '«, '■' •': • -polymer conformation and desorption, however the emulsions stabilized with.our new
technique remains remarkably stable. Figure 6 shows that the spacing between the droplets
of composition in Example VI remains the same over a period of ten months. .
From these results it is clear that the ferrofluid emulsions can be well stabilized by using following compositions:

Component Weight percentage

Possible Range Preferable range
Emulsion 1-40 7-14
Aqueous phase 47- 98.9 84.88- 92.09
Block copolymer 0.001-5 0.9-1.1
Surfactant 0.05-8 0.01-0.02
Example VII: Associative polymer stabilization (TVA 155K with TTAB )
Fig.7 shows the force profiles, obtained at different time intervals, for ferrofluid emulsion stabilized with PVA 155K of 0.5% with 5.1mM TTAB . It can be seen that the decay length and the onset of repulsion remains unchanged even after 10 months, indicating the long term stability during the storage period. Normally, the emulsions stabilized with conventional steric stabilization show hysterisis with time due to change in polymer conformation and desorption, however the emulsions stabilized with our new technique remains remarkably stable. Figure 7 shows that the spacing between the droplets of composition in Example VII remains the same over a period often months.
From these results it is clear that the ferrofluid emulsions can be well stabilized by using following compositions:

Component Weight percentage

Possible Range Preferable range
Emulsion 1-40 7-14
Aqueous phase 47- 98.9 84.5- 92
Block copolymer 0.001-5 0.9-1.1
Surfactant 0.05-8 0.1-0.4
19
Example VIII: Associative polymer stabilization (PVA 155K with NP10 )
Fig. 8 shows the force profiles, obtained at different time intervals, for ferrofluid emulsion stabilized with PVA 155K of 0.5% with 5 mM NP10.' It can be seen that the decay length and the onset of repulsion remains unchanged even after 10 months, indicating the long term stability during the storage period. Figure 8 shows' that the spacing between the droplets of composition in Example VIII remains the same over a period of ten months.
From these results it is clear that the ferrofluid emulsions can be well stabilized by using following compositions:

Component Weight percentage

Possible Range Preferable range
Emulsion 1-40 7-14
Aqueous phase 47-98.9 83.9-92.0
Block copolymer 0.001-5 0.9-1.1
Surfactant 0.05-8.0 0.1-1.0
Main Advantages of the Invention
The product Stabilized ferrofluid emulsions of the invention are stable and can be repeatedly used in the flux leakage probe for detecting and estimating defects in ferromagnetic materials for number of months or years.
The new process removes some of the inherent limitations of electrostatic and steric stabilization methods. At the same time, it has several additional merits compared to the existing stabilization techniques. The new process enable us to control the magnitude and onset of repulsion by simply adding very low concentrations of surfactants, which would ultimately provide better long-term stability for the colloidal formulation. This new process eliminates the need for choosing polymers with higher molecular weights (or high radius of gyration) for increasing the magnitude and range of repulsion. This not only makes the procedure of stabilization easy but also makes it cost effective.
The merits of the new process is summarized below:
• The spatial extension of the double layer is not sensitive to electrolyte concentration
• The decay length is insensitive to surfactant concentrations.

20
• Onset of repulsion can be tuned according to the requirement.
• No need for polymers with very large molecular weights to increase the onset of repulsion
• This procedure allows us to convert a low molecular weight neutral polymer into a high molecular weight polyelectrolyte or di-bloc polyelectrolyte.
The new process is suitable for obtaining colloidal dispersions with long-term stability, where the onset and the magnitude of repulsions can be precisely controlled, without changing the molecular weight of the macromolecules. In other words, this process allows us to covert a low molecular weight neutral polymer into a high molecular weight polyelectrolyte or di-bloc polyelectrolyte. The stabilization technique is particularly ideal for stabilizing ferrofluid-based emulsions. Here, we exploit the associative behavior of polymer with surfactants. The association of polymer-surfactant complexes leads to dramatic increase in the onset of repulsive force due to the stretched brush like conformation of adsorbed polymers. The force profiles in the presence of associative polymer follow an exponential scaling with a characteristic decay length, comparable to the radius of gyration of the free polymer. This decay length is weakly dependent on the surfactant concentration. Since the surfactant-polymer binding is a continuous process, onset of repulsion between the colloidal particles can be controlled precisely by choosing the amount of surfactants. Non-ionic polymers with a wide variety of cationic and anionic surfactants can be used in the above process.

21
We Claim
1. A stabilized magnetic emulsion of oil-in-water type comprising
(i) 1-40 wt. %, preferably 7-14 wt. % of a ferrofluid emulsion ;
(ii) 47- 98.95 wt. %, preferably 82.5- 92.5 wt. % of an aqueous phase (iii) 0.001-5 wt. %, preferablyr0.01- 1.5 wt. % of an emulsifying agent selected from anionic, cationic and non ionic surfactant and mixtures.theREof; and (iv) 0.05-8.0 wt. %, preferably 0.5-2.0 wt. % of a block copolymer with hydrophobic and hydrophilic groups with a molecular weight ranging from 4000 to 4 00 000.
2. A stabilized magnetic emulsion of oil-in-water type as claimed in claim 1 wherein, said ferrofluid emulsion comprising 75-95 wt %, preferably 80-90 wt % of ferrofluid oil, 2-12 wt %, preferably 5-10 wt % of outer surfactant and 2-11 wt %, preferably 4-9.5 wt % of water.
3. A stabilized magnetic emulsion of oil-in-water type as claimed in any of claims 1 or 2 wherein, said ferrofluid Oil is a suspension of 30-60 wt. %, preferably 40-50 wt. % of magnetic particles selected from iron, nickel, cobalt, gamma-FezO3, magnetite and combinations thereof and the like, 0.5-3 wt. %, preferably 1-2 wt. % of absorbed inner surfactants selected from oleic acid, phosphoric acid and 37-69.5 wt. %, preferably 48-59 wt. % of a carrier selected from n-octane, cyclohexane, n-dodecane, n-tetradecane, n-hexadecane, n-octadecane, kerosene and the like.

4. A stabilized magnetic emulsion of oil-in-water type as claimed in any of claims 1 to 3 wherein the size of said magnetic particles varies from 5 to 12 nm, preferably from 7 to 10 nm
5. A stabilized ferrofluid emulsion of oil-in-water type as claimed in any of claims I to 4 wherein said'outen surfactant is selected from conventional anionic, cationic or non-ionic surfactants. 22
6. A stabilized magnetic emulsion of oil-in-water type as claimed in any of claims 1 to 5 wherein said anionic surfactant is selected from polyoxyethylene, alkylphenyl ether sulfates, polyoxyethylene styrenated phenyl ether sulfates, alkylphosphates, polyoxyethylene alkyl ether phosphates, polyoxyethylene alkylphenyl ether phosphates, fatty acid salts, alkylbenzene sulfonates, alkyl sulfonates, alkyl naphthalene sulfonates, alpha -olefin sulfonates, dialkyl sulfosuccinates, alpha -sulfonated fatty acid salts,N-acyl-N-methyllaurate, alkylsulfates, sulfated lipids, polyoxyethylene alkyl ether sulfates and naphthalene sulfonate formaldehyde condensates.
7. A stabilized magnetic emulsion of oil-in-water type as claimed any of claims 1 to 6 wherein said cationic surfactant is selected from alkyltrimethyl ammonium salts, primary to tertiary aliphatic amine salts, dialkyldimethyl ammonium salts, trialkylbenzyl ammonium salts, alkyl pyridinium salts, tetraalkyl ammonium salts, and polyethylene polyamine fatty acid amide salts.
8. A stabilized magnetic emulsion of oil-in-water type as claimed in any of claims 1 to 7
wherein said nonionic surfactant is selected from polyoxyethylene polyoxypropylene
glycols, polyoxyethylene polyoxypropylene alkyl ethers, polyoxyethylene alkyl ethers,
polyoxyethylene alkenyl ethers, polyoxyethylene alkylphenyl ethers, polyoxyethylene
polystyrylphenyl ethers, polyhydric alcohol fatty acid partial esters, sorbitan fatty acid
esters, glycerol fatty acid esters, deca-glycerol fatty acid esters, polyglycerol fatty acid
esters, propylene glycol pentaerythritol fatty acid esters, polyoxyethylene sorbitan fatty
acid esters, polyoxyethylene glycerol fatty acid esters, polyoxyethylene polyhydric alcohol
fatty acid partial esters, polyoxyethylene fatty acid esters, polyglycerol fatty acid esters,
polyoxyethylenated castor oil, fatty acid diethanolamides, polyoxyethylene alkylamines,
triethanolamine fatty acid partial esters, trialkylamine oxides, and polyoxyalkylene group
containing organopolysiloxanes.
9. A stabilized magnetic emulsion of oil-in-water type as claimed in any of claims 1 to 8
wherein said hydrophobic group in said block copolymer is selected from vinyl acetate,
polysiloxane groups, polyfluro alkyl groups, legnine derivatives, poly propylene glycol
derivatives, polybutylene oxide and the like.
23
10. A stabilized magnetic emulsion of oil-in-water type as claimed in any of claims 1 to 9 . wherein said hydrophilic group in said block copolymer is selected from poly vinyl alcohol, poly saccharide, starch, cellulose, polyurethane, polyetheiyne.oxide and the like.
11. A stabilized magnetic emulsion of oil-in-water type as claimed in any of claims 1 to 10 wherein the ratio of said hydrophobic group and said hydrophilic group is 5:95, preferably 10:90 and more preferably 20:80.
12. A stabilized magnetic emulsion of oil-in-water type as claimed in any of claims 1 to 11 wherein said block copolymer is polyvinyl alcohol and vinyl acetate
13. A process of preparing a stabilized magnetic emulsion of oil-in-water type as claimed in any of claims 1 to 12 comprising
(i) preparing an emulsion by slowly adding oily phase into a premixed surfactant -
water mixture and shearing it in an emulsifier to get a crude emulsion; (ii) diluting the said crude emulsion repetitively with water containing surfactant at
CMC and fractionating the said crude emulsion to obtain monodispersed emulsion
with droplet size in the range of 100-1000 nm. (iii) adding said block copolymer into the said crude emulsion and incubating at 25°C
for atleast 72 hrs. (iv) adding further amount of same or different surfactant to the incubated crude
emulsion, obtained at the end of step 3 and mixing them thoroughly, (v) incubating the emulsion obtained at the end of step (iv) at 25-35°C for a further
period of atleast 1 hr to obtain a stabilized magnetic emulsion.
14.A process of preparing a stabilized magnetic emulsion of oil-in-water type as claimed in claim 13, wherein said shearing in step (i) is carried out at an rpm of 500 tolOOO for about 30 minutes.
15.A process of preparing a stabilized magnetic emulsion of oil-in-water type as claimed in claim 13, wherein the said further amount of same or different surfactant in step (iv) is 0.001 to 5 wt %; preferably 0.01 to 01.5 wt % of the said crude emulsion.
24
16. A stabilized magnetic emulsion of oil-in-water type and a process 'for preparing it .substantially as herein described in the text examples and drawings.
Dated this 17th day of December 2002

S. MAJUMDAR
S. MAJUMDAR & CO.
Applicant' Agent

Documents:

1134-mum-2002-claims(granted)-(19-12-2002).doc

1134-mum-2002-claims(granted)-(19-12-2002).pdf

1134-mum-2002-correspondence(12-01-2007).pdf

1134-mum-2002-correspondence(ipo)-(14-03-2007).pdf

1134-mum-2002-drawing(19-12-2002).pdf

1134-mum-2002-form 1(19-12-2002).pdf

1134-mum-2002-form 19(30-10-2003).pdf

1134-mum-2002-form 2(granted)-(19-12-2002).doc

1134-mum-2002-form 2(granted)-(19-12-2002).pdf

1134-mum-2002-form 3(19-12-2002).pdf

1134-mum-2002-power of attorney(28-07-2003).pdf

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Patent Number

205114

Indian Patent Application Number

1134/MUM/2002

PG Journal Number

42/2008

Publication Date

17-Oct-2008

Grant Date

14-Mar-2007

Date of Filing

19-Dec-2002

Name of Patentee

DEPARTMENT OF ATOMIC ENERGY

Applicant Address

ANUSHAKTHI BHAVAN, CHATHRAPARHY SHIVAJI MAHARAJ MARG, MUMBAI - 400001, MAHARASHTRA, INDIA.

Inventors:

#	Inventor's Name	Inventor's Address
1	1)JOHN PHILIP,2)TAMMANA JAYAKUMAR,3)PERUMAL KALYANASUNDARAM AND 4)BALDEV RAJ	METALLURGY & MATERIALS GROUP, NON-DESTRUCTIVE TESTING & EVALUATION SECTION, DIVISION FOR POST IRRADIATION EXAMINATION & NON-DESTRUCTIVE TESTING DEVELOPMENT, INDIRA GANDHI FOR ATOMIC RESEARCH, KALPAKKAM-TAMIL NADU, 603 102, INDIA.

PCT International Classification Number

B 01 D 17/00

PCT International Application Number

N/A

PCT International Filing date

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1			NA