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Gels d'émulsions à base d'huiles cristallisables : mécanismes de formation et propriétés rhéoloqiques

Abstract : The formation of crystals in the dispersed phase of an oil-in-water emulsion induces a morphological modifications of the dropplets interfaces which become rough and rippled. This phenomenon can give rise to dramatic rheological modifications like the transition from a fluid to a solid state. We show that the gelation of emulsions upon thermal treatment can be provoked by two distinct mechanisms: (i) partial coalescence caused by crystals located nearby the interfaces which irreversibly bridge neighbouring drops, and (ii) a jamming phenomenon due to the surface roughness hindering the relative displacements of droplets in contact. By performing experiments on model systems, we establish, that both the mechanism and kinetics of gelation are governed by the solid oil content, the drops diameter and the interface composition. In particular, we show that partial coalescence can be described as a percolation process requiring the creation of “solid versus liquid” contacts in between two drops. When submitted to a shear flow, the emulsions or gels exhibit two limiting behaviours: a macroscopic phase separation can be observed and/or a fragmented gel can be obtained with reduced level of connectivity. We study the influence of the parameters controlling the topological evolution.
The variety of accessible states makes these materials suitable for applications in different industrial fields like cosmetics or food.
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Florence Thivilliers. Gels d'émulsions à base d'huiles cristallisables : mécanismes de formation et propriétés rhéoloqiques. Matière Condensée [cond-mat]. Université Sciences et Technologies - Bordeaux I, 2007. Français. ⟨tel-00264651⟩

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