A parametric study on the application of microfluidics for emulsion characterization

Abstract

This work focuses on the application of a microfluidics system that has capability to produce monodispersed oil-in-water (O/W) and water-in-oil (W/O) emulsions for emulsion formation and stability analysis. Deionized water, aqueous solutions of inorganic salts, and aqueous solutions of surfactants were used as the water phase. N-decane, n-hexadecane, and surfactant solutions of n-decane and n-hexadecane were used as the oil phase. Experimental results indicating the effects of organic phase, continuous and droplet phase flow rates, water-cut, oil%, salt and surfactant types and concentrations on droplet size are presented. Emulsion stability experiments were carried out by observing droplet coalescence and temporal evolution of the droplet size. NaCl, KCl and CaCl2 salts were used to study the effect of salt type and concentration on the droplet size during the formation of O/W and W/O emulsions. The type and concentration of the inorganic salts studied have a negligible effect on the droplet size of both O/W and W/O type emulsions. However, for a given set of external phase and droplet phase velocities, oil droplet size is observed to be considerably larger than the aqueous phase droplet size. Oil soluble (Span 80) and water soluble (Sodium dodecyl sulfate) surfactants caused a significant reduction in droplet sizes for both O/W and W/O emulsions. It was also observed that the formation of droplets does not necessarily guarantee the stability of emulsions as rapid droplet coalescence occurs in some cases, especially in the absence or at low surfactant concentrations.