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Theses

Fabrication of Microcapsules through Surfactant-Free Emulsification

Abstract : This thesis presents a new process for the fabrication of microcapsules which is based on emulsification of non-miscible fluids, without using any surfactant. The only requirements are favorable interfacial energies, a viscosity ratio close to 1 between the inner phase (phase 1) and the liquid polymer that is used to make the shell (phase 2), and a viscosity ratio close to 1 between this liquid polymer (shell, phase 2) and the outer phase (phase 3).In this work, we designed capsules with a core made either of an aqueous solution of sodium alginate or of poly alpha olefin 40 oil. The shell is made of a free radical cross linkable aliphatic or epoxy urethane acrylate liquid polymer. These capsules are dispersed in an aqueous solution. We focus on their synthesis.In a first step, we characterize the physical properties of the fluids that are used to make the emulsions: density, interfacial tension and viscosity vs shear rate. Next, we determine experimentally the fragmentation diagram for single and the double emulsions by varying the viscosity ratios and the shear rates. We find that there is an optimum viscosity ratio Ƞ1/Ƞ2 between phase 1 and 2: this ratio= 0.8, which is close to 1. We also find that for the double emulsion the optimum viscosity ratio Ƞ2/Ƞ3 between phase 2 and 3 = 1.24, which is close to 1. We present microscope images and movies of the fragmentation of double emulsion droplets for both types of capsules.We used osmotic swelling to study the polymerization of the acrylate shell and we show how it depends on UV exposure time and initiator concentration. We characterize the microcapsules by measuring their size distribution. We determine the encapsulation efficiency for both types of capsules. In the case of capsules with an aqueous core it is 70%. This loss of efficiency is due to the fact that phase 1 and phase 3 have no interfacial tension since they are chemically identical. In the case of capsules with an oil core, it is 100%. This stability of the double emulsion originates from the high interfacial tension between the oil core (phase 1) and the glycerol (phase 3). Finally, we present four methods that make it possible to trigger the rupture of the capsules and the release of encapsulated material. These methods use different chemical or physical properties of the encapsulated material and of the polymer shell.
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Abdulwahed Shglabow. Fabrication of Microcapsules through Surfactant-Free Emulsification. Material chemistry. Université Paris sciences et lettres, 2019. English. ⟨NNT : 2019PSLET007⟩. ⟨tel-02631709⟩

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