Mixing of Liquid-liquid Non-Newtonian Fluids, Preliminary Results

Immiscible liquid-liquid suspensions, such as emulsions and polymer blends, are frequently encountered in a variety of applications, e.g., cosmetics and pharmaceuticals design, food processing, plastics technology. Mixing efficiency of such systems is greatly influenced by the property of the two phases, most of the fluids used by the industry show Non-Newtonian behavior. This work is concerned with the application of static mixers to form biphasic liquid dispersions in the laminar flow regime; in particular we present here a methodology to investigate the effect on the mixing efficiency of elasticity of one phase. To this aim, two low viscosity Boger fluids, obtained by mixing small amount of Polyacrilamide and Xantan gum in a Newtonian glycerin-water solvent, were used as aqueous phase and mixed with silicon oils of different molecular weight. In order to quantify the influence of viscoelasticity on the mixing efficiency, a reference Newtonian fluid (GLY) obtained by mixing water and glycerin in an appropriate concentration to obtain the same viscosity of the non-Newtonian reference was used. The mixing efficiency has been quantified by measuring the drop size distribution by optical microscopy and image analysis. The expected influence of the elasticity is to delay break-up phenomena, so resulting in a lower mixing efficiency, the effect is expected to be limited when the elasticity is only in the drop phase, compared to the case of elastic matrix. Below the drop size distribution for the case of aqueous disperse phase in SO is reported; on the left graph the numerical distribution is compared for Newtonian GLY and non-Newtonian XGh and PAA, on the right one the cumulative volumetric shows that the differences are limited to the large diameter tail of the distribution, that represents most of the dispersed phase volume.