Compressibility and Elasticity of Concentrated Emulsions

Abstract

Emulsions are dispersions of deformable droplets which can therefore span droplet volume fractions from zero to almost one. Much effort has been spent in studying the rheology of relatively dilute emulsions (oil volume fraction φ below 40%) [1], and references therein, [2, 3]). At low volume fraction, nonadhesive emulsions consist of unpacked spherical droplets; such samples generally show a Newtonian flow, while flocculated emulsions show shear-thinning behavior. However, owing to the deformability of liquid droplets, emulsions may be concentrated up to volume fractions much higher than the volume fraction φ* corresponding to the random close packing of hard spheres. For randomly packed monodisperse spheres, φ* = 0.64. Emulsions are generally composed of fluids only, but at high internal-phase volume fractions (at which the droplets can no longer pack without deforming) they become rigid and resemble an elastic solid. This chapter aims to describe the basic physics of the compressibility and elasticity of such dense emulsions.