Heterogeneous liquid sheets: from emulsions to suspensions

Multiphase fluids such as emulsions and suspensions are involved in industrial spraying and atomization processes, including pesticide application and spray painting. The dispersed phase is known to alter the effective viscosity of the liquid in the continuum approximation. Yet atomization processes confine the multiphase fluids between interfaces, over length scales comparable to the drop or particle size. To determine the limitations of the effective viscosity approach to describe atomization processes, we conduct drop impact experiments on a small target. Upon impact, a transient liquid sheet of pure fluid, emulsion, or suspension expands radially before breaking into secondary droplets. We use high-speed imaging to record and compare the expansion and retraction of the self-suspended sheets. Our study finds that the effective viscosity fails to capture the complex dynamics of multiphase liquid sheet. The interactions between the dispersed phase and the air/liquid interfaces contribute to the dynamics of the liquid sheet and depend on whether the dispersed phase is a solid or a liquid.