The effect of emulsifier concentration on turbulent drop breakup - An experimental study based on single drop visualizations.

HYPOTHESIS

A modified Weber number can capture the effect of emulsifier concentration and the effect of external stress in turbulent drop breakup. Moreover, the effect of emulsifiers on turbulent drop breakup cannot be adequately understood from classic slow/laminar techniques and quasi steady state interfacial tension.

EXPERIMENTS

Single drop breakup visualizations are used to study the effect of polysorbate 20 on turbulent drop deformation and breakup. Comparisons are made to drop tensiometry and emulsification experiments.

FINDINGS

A high concentration of the emulsifier increases breakup probability and breakup rate and decreases breakup timescales. These effects scale with a Weber number, indicating a lowering of the effective interfacial tension to 71 % of its pure interface value. This is far less than the observed lowering of interfacial tension as measured by quiescent drop tensiometry. Mechanistically, this shows that adsorption during emulsification cannot be limited by diffusion. Studying the effect cross a range of emulsifier concentrations suggest an elastic resistance at intermediate concentrations, further helping to understand the origin of similar effects previously reported in emulsification experiments. Overall, the results show the need to study emulsifiers under turbulent conditions to understand their effects during emulsification, as opposed to the slow/laminar techniques previously used.