Effect of Continuous and Discontinuous Droplet-Size Distributions on the Viscosity of Concentrated Emulsions in Premix Membrane Emulsification

Abstract

The dispersed phase volume fraction of concentrated emulsions can be substantially increased without a considerable increase in viscosity by optimizing the droplet-size distribution (DSD) of emulsion mixtures. However, due to the limitations of the traditional methods to control the DSD, the study of its effect on the viscosity of emulsion mixtures is usually limited. The premix membrane emulsification method was used to prepare a droplet-size-controlled concentrated emulsion, and the DSD's effect on the viscous behavior of emulsion mixtures was investigated. It was observed that widening the DSD led to a decrease of the viscosity at lower shear rates, while at higher shear rates, a shear-thickening behavior was observed. In a discontinuous DSD, there was a tendency for the viscosity to decrease to a minimum value at about 75% mixing fraction of larger-droplet-size emulsions beyond which the viscosity increased until the monomodal packing limit. The viscosity could be decreased by more than 20-fold in bimodal emulsions depending on the droplet size ratio. Mixing emulsions of different DSDs enabled attaining a viscosity lower than that of the monodispersed parent emulsions.