Pre-holes and holes: heterogeneities in liquid sheets of emulsion

Industrial and agricultural processes rely on sprays to deliver fluid to surfaces. A common way to tune the size of the spray droplets is by varying the composition of the liquid. For example, oil droplets in an aqueous phase modify the atomization dynamics and the size distribution of the secondary droplets. Observations of self-suspended liquid sheets indicate that the destabilization occurs as the sheet thickness becomes highly heterogeneous with isolated regions of low to zero thickness. To understand how the immiscible dispersed phase leads to thickness heterogeneities and eventually different spray properties, we investigate the dynamics of pre-holes (thin regions) and holes. We track the nucleation, position, and growth of pre-holes and holes as a function of the oil volume fraction, surface tension, and viscosity. We find that the growth rate of pre-holes decreases with oil phase viscosity and surface tension. Our findings demonstrate that the competition between viscous and capillary effects controls the formation and growth of heterogeneities in liquid sheets.