EMULSION COMPRISING SIZE-CONTROLLED DROPLETS

Abstract

An emulsion including size-controlled droplets dispersed in a viscoelastic continuous phase including a polymer in solution in a solvent, wherein the viscoelastic continuous phase presents a ratio between the viscous modulus (G) and the elastic modulus (G) ranging from 0.2 to 10 and wherein the mean diameter of the droplets is proportional to the G/G ratio with 1.5 as exponent. Also, a process for the fabrication of size-controlled droplets in a viscoelastic continuous phase of an emulsion, and the use of the emulsion in applications requiring size-controlled droplets.

Claims

1-13. (canceled)

14. An emulsion comprising droplets dispersed in a viscoelastic continuous phase, said droplets having a mean diameter Dn.sub.50 inferior to 100 m, wherein said droplets are size-controlled, said viscoelastic continuous phase comprising at least one polymer in solution in at least one solvent and at a concentration ranging from 1 to 20% by weight of said at least one polymer in respect to the total weight of the viscoelastic continuous phase, wherein said at least one polymer is selected from cellulose derivatives, polyacrylates, polyacrylamides, polyethylene oxide, polysaccharides, protein derivatives, silicone derivatives and a mixture thereof, provided that said at least one polymer is not an alginate, wherein said viscoelastic continuous phase present a ratio between the viscous modulus (G) and the elastic modulus (G) ranging from 0.2 to 10.

15. The emulsion according to claim 14, wherein said viscoelastic continuous phase does not comprise a surfactant.

16. The emulsion according to claim 14, wherein said polymer is selected from chitosan, carboxymethyl cellulose, methyl cellulose, guar gum, konjac gum, polyacrylic acid, polyethylene oxide and a mixture thereof.

17. The emulsion according to claim 14, wherein said droplets are size-controlled monodisperse droplets, and wherein said G/G ratio is ranging from 1 to 5.

18. The emulsion according to claim 14, wherein said droplets are size-controlled monodisperse droplets, and wherein said G/G ratio is ranging from 1 to 3.

19. The emulsion according to claim 14, wherein said droplets have a mean diameter ranging from 1 to 70 m.

20. The emulsion according to claim 14, wherein said droplets have a mean diameter ranging from 5 to 20 m.

21. The emulsion according to claim 14, wherein said viscoelastic continuous phase further comprises at least one Newtonian fluid.

22. The emulsion according to claim 14, wherein the dispersed phase comprises at least one crosslinkable material and optionally at least one initiator.

23. The emulsion according to claim 22, wherein the dispersed phase further comprises at least one non-miscible active agent.

24. A process for the manufacture of an emulsion according to claim 14, comprising a step of submitting the dispersed droplets to an elongation-fragmentation mechanism in the viscoelastic continuous phase.

25. The process according to claim 24, wherein a shear rate ranging from 1 to 20000 s.sup.1 is applied during the elongation-fragmentation step.

26. The process according to claim 24, wherein a shear rate ranging from 1 to 1000 s.sup.1 is applied during the elongation-fragmentation step.

27. The process according to claim 24, further comprising a step of addition of a Newtonian fluid into the viscoelastic continuous phase.

28. A process for the fabrication of microcapsules comprising the steps of: manufacturing an emulsion as described in claim 24, and cross-linking the formed droplets.

29. The process according to claim 28, wherein the cross-linking of the formed droplets is performed by photopolymerization of said emulsion.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0165] FIG. 1 is a graph showing the variation of the mean diameter (D) and size distribution of the formed droplets as a function of G/G ratio at the working angular frequency for materials of Table 1 (filled circles) and Table 2 (open squares). Data points correspond to the mean diameter (D) and error bars correspond to the standard deviation of the size distribution. The dotted line corresponds to the equation (1).

[0166] FIG. 2 is a graph showing the evolution of the G/G ratio as a function of the product .sub.(1%).Math.C for the materials of Table 1. The dotted line corresponds to the equation (2).

[0167] FIG. 3 is a graph showing the variation of the mean diameter (D) and size distribution of the formed droplets as a function of the ratio ii/n for the samples in Table 2. Data points correspond to the mean diameter (D) and error bars correspond to the standard deviation of the size distribution. The dotted line corresponds to equation (3).

EXAMPLES

[0168] The present invention is further illustrated by the following examples.

[0169] All percentages mentioned for the compositions in the examples are weight percentages in respect to the total weight of the composition.

[0170] In all following examples, a dispersed phase composed of polyester polymer (CN2035, Sartomer) 92%, hexanediol diacrylate 5% and Darocur 1173 (Aldrich) 3% was used. This mixture is Newtonian with .sub.i; =32000 mPa.Math.s.

[0171] An emulsion made of 5% of this dispersed phase in various types of continuous phases was formed by applying a 500 s.sup.1 shear rate for one minute using a sawtooth impeller. Immediately after the shear rate was stopped, the formed droplets were cross-linked under UV light in order to freeze the system before ageing such as coalescence and growth could occur. It was therefore possible to measure the size distribution of the formed droplets as it is right after the application of shear, by means of image analysis of microscopy pictures of the cross-linked emulsions.

[0172] The monodispersity/polydispersity and size control of the formed droplets as a function of the continuous phase properties were observed and compared.

Example 1: Droplets Formation in Viscoelastic Media (0.2<G/G<10)

[0173] A variety of polymers solubilised in water were used as continuous phases, whose nature and properties are summarised in Table 1.

[0174] Results

[0175] These polymer systems enable the formation of droplets with a mean diameter D ranging from 5 to 70 m. These droplets are size-controlled as the mean diameter can be predicted from equation (1) mentioned above. The size distribution is found to be polydisperse when G/G is below 0.2 and monodisperse when G/G is above 0.2.

[0176] FIG. 1 (filled circles) shows the variation of the mean diameter (D) and size distribution of the formed droplets as a function of G/G ratio at the working angular frequency for materials of Table 1. Data points correspond to the mean diameter (D) and error bars correspond to the standard deviation of the size distribution. The black dotted line corresponds to the equation (1).

[0177] FIG. 1 shows that: [0178] If 0.2<G/G<1, a polydisperse population of size-controlled droplets is formed. [0179] If 1 G/G<10, a monodisperse population of size-controlled droplets is formed by an efficient elongation-fragmentation mechanism with a typical diameter below 20 m.

[0180] Moreover, it was found that the ratio G/G varies with the product .sub.(1%).Math.C verifying equation (2) mentioned above.

[0181] FIG. 2 shows the evolution of the G/G ratio as a function of the product n.sub.(1%).Math.C for the materials of Table 1. The grey dotted line corresponds to the equation (2).

[0182] FIG. 2 shows that: [0183] If .sub.(1%).Math.C<1 000 mPa.Math.s, a monodisperse population of size-controlled droplets is formed and the continuous phase belongs to the predominant viscous regime. [0184] If 1 000 mPa.Math..sub.(1%).Math.C<100 000 mPa.Math.s, a polydisperse population of size-controlled droplets is formed.

TABLE-US-00001 TABLE 1 .sub.(1%) Materials Supplier Chemistry (mPa .Math. s) C (%) .sub.(1%) .Math. C G/G.sub.( = 100 rad/s) Konjac Roeper Konjac 90 000 1 90 000 0.23 36000 Carbomer Adara Polyacrylic 40 000 1.5 60 000 0.23 141 acid CMC 4570 Roeper Carboxymethyl 20 000 1.5 30 000 0.4 cellulose CMC 4520 Roeper Carboxymethyl 200 5 1000 0.78 cellulose CMC 4500 Roeper Carboxymethyl 60 8 480 0.92 100-200 cellulose Polyox WSR Dow Polyethylene 70 5 350 1.12 205 oxyde Chitosan Chitosan Chitosan 20 5 100 1.13 lab CMC 4500 Roeper Carboxymethyl 20 13.5 270 1.13 20-50 cellulose Chitosan Chitosan Chitosan 33 10 330 1.15 lab CMC 4520 Roeper Carboxymethyl 200 3.4 680 1.16 cellulose Methocel Dow Methyl 80 5 400 1.25 A4C cellulose Chitosan Chitosan Chitosan 20 10 200 1.41 lab

[0185] Example 2: Droplet formation in Newtonian fluids (G/G>10) A variety of polymers were used as continuous phases with Newtonian behavior (G/G>10): hydrophobically modified ethoxylate-urethane copolymer (Optiflo T1000 and Optiflo L1400, Byk) and hydrophobically modified polyacetal-polyether copolymer (Aquaflow NHS300E, Ashland). The composition and viscosity of the different samples made are summarised in Table 2.

TABLE-US-00002 TABLE 2 Composition (mPa .Math. s) Aquaflow NHS300E 58% 900 Water 42% Optiflo T1000 70% 1 100 Water 30% Aquaflow NHS300E 75% 2 200 Water 25% Optiflo L1400 80% 4 000 Water 20% Optiflo L1400 85% 4 700 Water 15% Optiflo L1400 8 000 Aquaflow NHS300E 9 000

[0186] Results

[0187] If G/G>10, the polymer solution behaves like a purely viscous Newtonian fluid. Thus, the mean diameter D does not depend on the G/G ratio and the size distribution remain broad.

[0188] All prepared continuous phases have a purely viscous behavior, and the diameter D of the formed droplets verifies equation (3), in which a is the surface tension, the viscosity of the continuous phase and Y the shear rate. In particular, D does not depend on the G/G ratio:

D/()(3)

[0189] The size distribution of the droplet population was found to be polydisperse.

[0190] FIG. 3 shows the variation of the mean diameter (D) and size distribution of the formed droplets as a function of the ratio .sub.i/ for the samples in Table 2. Data points correspond to the mean diameter (D) and error bars correspond to the standard deviation of the size distribution. The dotted line corresponds to equation (3).

Example 3: Insufficient Fragmentation to Form Droplets (G/G<0.2)

[0191] Two different polymers solubilised in water were used as continuous phases, whose nature and properties are summarised in Table 3.

TABLE-US-00003 TABLE 3 .sub.(1%) Materials Supplier Chemistry (mPa .Math. s) C (%) .sub.(1%) .Math. C G/G.sub.( = 100 rad/s) Guar 3500 Roeper Guar 20 000 5 100 000 0.15 CMC 4570 Roeper Carboxymethyl 20 000 6 120 000 0.18 cellulose

[0192] Results

[0193] In these systems wherein G/G<0.2 and .sub.(1%).Math.C >100 000 mPa.Math.s no droplets could be formed, showing that the elastic modulus is too high for efficient fragmentation.

Example 4: Addition of a Newtonian Fluid in the Continuous Phase

[0194] Different mixtures of a chitosan (Chitosanlab) solution at 5% in water and Optiflo L1400 (Byk) were used as continuous phases. Their composition and properties are summarised in Table 4.

[0195] Results

[0196] These polymer systems enable the formation of droplets with a mean diameter D below 10 m. These droplets are size-controlled as the mean diameter can be predicted from equation (1) mentioned above. The size distribution is found to be monodisperse which is consistent with the fact that G/G is above 0.2. These results can be visualised in FIG. 1 (open squares).

[0197] Moreover, it is found that G/G increases linearly with the concentration of the Newtonian fluid.

TABLE-US-00004 TABLE 4 Chitosan 5% Optiflo L1400 Materials Conc. (%) Conc. (%) G/G.sub.(=100 rad/s) 1 100 0 1.13 2 97.5 2.5 1.2 3 95 5 1.28 4 90 10 1.36 5 80 20 1.43 6 60 40 1.58