DOUBLE EMULSION AND CAPSULES

Abstract

A method for the manufacture of a water-in-oil-in-water double emulsion, which includes a step of adding dropwise an aqueous phase to an oil phase until a catastrophic inversion. Also, a water-in-oil-in-water double emulsion, a method for preparing solid microcapsules from a water-in-oil-water double emulsion having oligomers and/or monomers in the oil phase.

Claims

1-18. (canceled)

19. A method for the manufacture of a water-in-oil-in-water double emulsion, wherein said double emulsion is surfactant-free, comprising: a step of adding dropwise an aqueous phase to an oil phase, wherein the adhesion energy between two droplets of aqueous phase dispersed in the oil phase ranges from 10.sup.5 J.Math.m.sup.2 to 10.sup.3 J.Math.m.sup.2, said step of adding the aqueous phase to the oil phase being performed until a catastrophic inversion occurs.

20. The method according to claim 19, wherein the addition dropwise of the aqueous phase to the oil phase occurs at a rate ranging from 0.001 mL.Math.s.sup.1 to 50 mL.Math.s.sup.1.

21. The method according to claim 19, wherein the mixture comprising the aqueous phase and the oil phase is continuously stirred.

22. The method according to claim 19, wherein the mixture comprising the aqueous phase and the oil phase is continuously stirred at a stirring speed ranging from 100 rpm to 3000 rpm.

23. The method according to claim 19, wherein the shear rate applied during stirring ranges from 1000 s.sup.1 to 4000 s.sup.1.

24. The method according to claim 19, wherein the ratio between the dynamic viscosity of the innermost aqueous phase and the viscosity of the oil phase ranges from 0.01 to 20, the dynamic viscosities being measured using a TA Instruments AR-G2 rheometer equipped with a 3 cm diameter, 2-degree angle cone and a temperature control cell set at 25 C.

25. The method according to claim 19, wherein the interfacial tension between the aqueous phase and the oil phase ranges from 0 J.Math.m.sup.2 to 5010.sup.3 J.Math.m.sup.2.

26. The method according to claim 19, wherein the oil phase comprises at least one compound selected from oligomers, monomers and mixtures thereof, and optionally at least one photo initiator.

27. A water-in-oil-in-water double emulsion obtained by the method according to claim 19.

28. A water-in-oil-in-water double emulsion, comprising one innermost aqueous phase, one external aqueous phase and one oil phase, wherein the innermost aqueous phase is entrapped in the oil phase and the external aqueous phase entraps the oil phase, wherein the two aqueous phases comprise the same composition, wherein said double emulsion is surfactant-free, and wherein the adhesion energy between two droplets of the innermost aqueous phase dispersed in the oil phase ranges from 10.sup.5 J.Math.m.sup.2 to 10.sup.3 J.Math.m.sup.2.

29. The water-in-oil-in-water double emulsion according to claim 28, wherein the ratio between the dynamic viscosity of the innermost aqueous phase and the viscosity of the oil phase ranges from 0.01 to 20, the dynamic viscosities being measured using a TA Instruments AR-G2 rheometer equipped with a 3 cm diameter, 2-degree angle cone and a temperature control cell set at 25 C.

30. The water-in-oil-in-water double emulsion according to claim 28, wherein the interfacial tension between the aqueous phase and the oil phase ranges from 0 J.Math.m.sup.2 to 5010.sup.3 J.Math.m.sup.2.

31. The water-in-oil-in-water double emulsion according to claim 28, wherein the oil phase comprises at least one compound selected from oligomers, monomers and mixtures thereof, and optionally at least one photo initiator.

32. A method for preparing solid microcapsules comprising the steps of: a) manufacturing a water-in-oil-in-water double emulsion according to the method according to claim 19, wherein the oil phase comprises at least one compound selected from oligomers, monomers and mixtures thereof and optionally at least one photo initiator, and then b) crosslinking the oligomers and/or monomers of the oil phase.

33. The method according to claim 32, wherein the step b) of crosslinking is carried out by submitting the double emulsion to a source of light.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0206] FIG. 1 represents two pictures from microscopic observation of an emulsion before and after phase inversion, whose water/oil system is glycerol (1 Pa.Math.s)/silicone (1 Pa.Math.s). FIG. 1a) illustrates the emulsion before inversion (<max) and FIG. 1b) illustrates the emulsion after inversion (=max).

[0207] FIG. 2 is a graph showing the evolution of max depending on the viscosity ratio p for two different water/oil systems: one with PDMS as oil phase and pure glycerol as aqueous phase (curve represented by solid squares), the other with PDMS as oil phase and a 95% (w/w) glycerol solution as aqueous phase (curve represented by empty triangles).

[0208] FIG. 3 is a graph showing the evolution of max depending on the viscosity ratio p at two stirring rates (500 rpm and 2000 rpm) for a water/oil system comprising glycerol as aqueous phase and silicone oil as oil phase.

[0209] FIG. 4 represents three pictures from microscopic observation of an emulsion showing the evolution of until max is achieved, the water/oil system comprising glycerol as aqueous phase and silicone oil as oil phase and having a viscosity ratio p of about 1, the stirring speed being of 500 rpm. In FIG. 4a), =10% w/w. In FIG. 4b), =75% w/w. In FIG. 4c), =85% w/w.

[0210] FIG. 5 represents two pictures from microscopic observation of an emulsion showing the evolution of until max is achieved, the water/oil system comprising glycerol as aqueous phase and silicone oil as oil phase and having a viscosity ratio of about 0.1, the stirring speed being of 500 rpm. In FIG. 5a), =20% w/w. In FIG. 5b), =40% w/w.

[0211] FIG. 6 is a graph showing the evolution of max depending on the viscosity ratio p at a stirring rate of 500 rpm for a water/oil system comprising a 95% (w/w) aqueous glycerol solution as aqueous phase and silicone oil as oil phase.

[0212] FIG. 7 is a graph showing the evolution of max depending on the viscosity ratio p at a stirring rate of 500 rpm for a water/oil system comprising a PEG20000 aqueous solution (26% w/w) (0.1 Pa.Math.s) as aqueous phase and silicone oil as oil phase.

[0213] FIG. 8 is schematic representation of the method of determining the adhesion between two drops comprising the use of a micropipette aspiration for adhesion testing.

EXAMPLES

[0214] The present invention is further illustrated by the following examples.

Example 1: Impact of the Adhesion Energy Between Two Droplets of Aqueous Phase Dispersed in the Oil Phase on Inverse Emulsions Formulated

Materials and Methods

[0215] Different water/oil systems were studied. Each system has a given dynamic viscosity ratio p which is about 1. For each system, no surfactant was added.

[0216] In order to obtain an inverse emulsion, for each water/oil system, the aqueous phase was slowly added, using a syringe (typical diameter of the drop: 2 m), to a given starting volume of the oil phase in a container comprising an overhead stirrer with an anchor geometry (the stirrer diameter being 45 mm, stirring speed being 500 rpm), at a temperature of 25 C.

[0217] After each addition step of the aqueous phase, an aliquot of the water/oil mixture was taken and observed under the microscope. For each system, max was determined and the morphology of the inverse emulsion was checked.

Results

[0218] The results are presented in the following Table 1:

TABLE-US-00001 TABLE 1 The silicone oil used in the following table has a Molecular weight of 30 000 g/mol. Adhesion energy between two droplets of aqueous phase dispersed in the oil phase Surface ranging from tension 10.sup.5 J .Math. m.sup.2 to Phase Oil phase Aqueous phase (mN/m) 10.sup.3 J .Math. m.sup.2 inversion Silicone oil Glycerol (1 Pa .Math. s) 25.3 Yes: 3.1 10.sup.5 Double (equivalent to J .Math. m.sup.2 emulsion PDMS) (from 0.1 Pa .Math. s to 30 Pa .Math. s) Silicone oil PEG20000 Yes: 1.4 10.sup.5 Double (equivalent to aqueous solution J .Math. m.sup.2 emulsion PDMS) (from (26% w/w) (0.1 0.1 Pa .Math. s to 30 Pa .Math. s) Pa .Math. s) Silicone oil Alginate aqueous 40 Yes: 1.4 10.sup.5 Double (equivalent to solution (1 .Math. ) J .Math. m.sup.2 emulsion PDMS) (from 0.1 Pa .Math. s to 30 Pa .Math. s) Mineral oil (1 Glycerol (1 .Math. ) 28.5 No* Simple Pa .Math. s) emulsion *The value of adhesion energy between the two droplets of aqueous phase dispersed in the oil phase for the system glycerol (1 Pa .Math. s) / mineral oil (1 Pa .Math. s) could not be determined because the system was not stable, so there was no double drop and the continuous film method was not applicable.

[0219] As it can be seen in Table 1, there is a relation between the adhesion energy between two droplets of aqueous phase dispersed in the oil phase, and the type of phase inversion. Indeed, when the adhesion energy between two droplets of aqueous phase dispersed in the oil phase ranges from 10.sup.5 J.Math.m.sup.2 to 10.sup.3 J.Math.m.sup.2, the phase inversion leads to the obtainment of a double emulsion, whereas when the adhesion energy between two droplets of aqueous phase dispersed in the oil phase does not range from 10.sup.5 J.Math.m.sup.2 to 10-3 J.Math.m.sup.2, the phase inversion leads to the obtainment of a simple emulsion.

[0220] In addition, FIG. 1 illustrates that, starting from a glycerol-in-silicone emulsion in which the viscosity ratio p is about 1 (p1) (FIG. 1a), <max), by reaching max, the emulsion does not phase invert into a simple emulsion as expected but turned into a double emulsion of glycerol/silicone/glycerol (FIG. 1b), q=max).

Example 2: Influence of the Dynamic Viscosity Ratio on Inverse Emulsions Formulated

Materials and Methods

[0221] Three different water/oil systems were studied. For each system, no surfactant was added.

[0222] In order to obtain inverse emulsions, for each water/oil system, the aqueous phase was slowly added, using a syringe (typical diameter of the drop: 2 m), to a given starting volume of the oil phase in a container comprising an overhead stirrer with an anchor geometry (the stirrer diameter being 45 mm, stirring speed being 500 rpm), at a temperature of 25 C.

[0223] After each addition step of the aqueous phase, an aliquot of the water/oil mixture was taken and observed under the microscope. For each system, max was determined and the morphology of the inverse emulsion was checked.

Results

[0224] The results are presented in the following Table 2 and in FIGS. 2 to 7.

TABLE-US-00002 TABLE 2 The silicone oil used in the following table has a Molecular weight of 30 000 g/mol. Adhesion energy between two droplets of aqueous phase dispersed in the oil phase ranging from System 10.sup.5 J .Math. m2 to Phase number Oil phase Aqueous phase 10.sup.3 J .Math. m.sup.2 inversion 1 Silicone oil Glycerol (1 Pa .Math. s) Yes: 3.1 10.sup.5 Double (equivalent to J .Math. m.sup.2 emulsion PDMS) (0.1 Pa .Math. s to 30 Pa .Math. s ) 2 Silicone oil 95% (w/w) Yes: 3.1 10.sup.5 Double (equivalent to aqueous J .Math. m.sup.2 emulsion PDMS) (0.1 Pa .Math. s to glycerol solution 30 Pa .Math. s ) (350 mPa .Math. s ) 3 Silicone oil PEG20000 Yes: 1.4 10.sup.5 Double (equivalent to aqueous solution J .Math. m.sup.2 emulsion PDMS) (0.1 Pa .Math. s to (26% w/w) (0.1 30 Pa .Math. s ) Pa .Math. s )

[0225] Systems number 1 (glycerol/silicone oil (0.1 Pa.Math.s to 30 Pa.Math.s)): as it can be seen in FIG. 2, FIG. 3, FIG. 4 and FIG. 5, it was noticed that max highly depends on the viscosity ratio p. Elevated max (i.e. of equal to or greater than 64% w/w) is favored when p is in the order of 1 or greater than or equal to 1. For p being about 3, max is equal to 95% w/w. When max is equal to 95% w/w, the obtained double emulsion showed a remarkable metastability of the internal emulsion which lasted at least one day. As it can be seen in FIG. 2, at low dynamic viscosity ratio (p<1), when the outer oil phase is more viscous than the inner aqueous phase, the resulting inverting double emulsion could not be concentrated to more than 70% w/w in innermost aqueous phase (p<70% w/w). By increasing the viscosity ratio, more innermost aqueous phase could be incorporated in the intermediate oil phase. In particular, for p>1, could reach 90% w/w, which is surprising. In addition, it can be seen in FIG. 3 that max also depends on the rotation speed.

[0226] For system numbers 2 and 3, as it can be seen respectively in FIG. 6 and FIG. 7, it was noticed that max highly depends on the viscosity ratio p.