Dextranes amphiphiles : adsorption aux interfaces liquide/liquide et application à la stabilisation d'émulsions

Abstract : Oil-in-water emulsions are thermodynamically uns table systems that can be kinetically stabilized by the use of water soluble surfactants. ln the frame of our studies, we have used amphiphilic derivatives of dextran, a neutral polysaccharide. Hydrophobically modified dextrans are interesting for their biocompatibility and biodegradability and convenient for biomedical applications. Moreover they exhibit good surface active and emulsifying properties. The polymeric emulsifiers were synthesized by reacting aliphatic epoxides with dextran's hydroxyl groups. A family of water-soluble modified dextran was obtained varying their molecular weight, the length and the amount of grafted alkyl chains. Some of modified dextran were also modified by ionic groups thanks to the attachment of sodium sulfopropyl. The kinetics of interfaciql tension lowering was then determined with a dynamic tensiometer. By means of semi-empirical equation, the equilibrium value of interfacial tension was obtained by extrapolation to infinite time. The influence of different parameters has been investigated. These studies in tensiometry are supplemented by experiments in interfacial rheology which informs about the elasticity of adsorbed polymer layer. Oil-in-water emulsions were prepared by sonication in the presence of polymeric surfactants in the aqueous phase. Initial droplet size, thickness of the pol ymer layer and the amount of adsorbed pol ymer were determined in different emulsification conditions. Finally, the evolution of the average droplet size as a function of time allowed concluding that emulsion ageing occurred by Ostwald ripening. The rate of Ostwald ripening is directly proportional to the interfacial tension value at equilibrium as predicted by the equation of Lifshitz, Slyozov and Wagner.
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Élise Rotureau. Dextranes amphiphiles : adsorption aux interfaces liquide/liquide et application à la stabilisation d'émulsions. Autre. Institut National Polytechnique de Lorraine, 2005. Français. ⟨NNT : 2005INPL019N⟩. ⟨tel-01749820⟩

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