Dynamics of emulsion drop impact, spreading and evaporation: the effect of internal phase gelation

The dynamics of drop impact, spreading, and evaporation on solid surfaces are fundamental to many processes, including agricultural spraying, printing, combustion, and coating. While these behaviors are well understood for single phase liquids, less is known about emulsions with complex internal structures. Here, we report an experimental study on the dynamics of water-in-oil emulsion droplets containing either liquid or gelled aqueous phases. The continuous phase is composed of n-heptane and Span 80 micelles, while the dispersed phase is a reactive sodium silicate-ammonium bicarbonate solution that undergoes gelation. Internal gelation changes the rheological response of the dispersed phase and therefore modifies dissipation during spreading and drying. During the impact stage, the dynamics are similar for both emulsion types within our experimental resolution, whereas during the subsequent spreading stage, gel-containing emulsions reach smaller wetted areas. Measured maximum spreading factors are broadly consistent with unified inertial-capillary-viscous scaling for water emulsions, while gel emulsions show systematic deviations at higher internal-phase fractions. Bottom-view fluorescence imaging reveals distinct drying patterns: isolated circular deposits for water emulsions and rugged, interconnected structures for gel emulsions. These findings highlight the importance of the internal droplet structure in governing impact and drying dynamics, with implications for a wide range of emulsion-based technologies.