Dual nature of volatility on drop wetting dynamics of acetone–isopropanol mixtures on ultrathin smooth oil films

Abstract

Volatile drop impacts are commonplace among various industrial and natural processes and most often studied under Leidenfrost conditions, where a vaporized film sustains the drop weight or reverses drop momentum. The vapor thrust generated is therefore a function of the enthalpy of vaporization, the superheat, specific heat capacity of the vapor, vapor thermal diffusivity, and the vapor film thickness. In this study, volatile drop impact and wetting dynamics of acetone and isopropanol mixtures at normal temperature and pressures were shown to generate enough thrust from evaporation alone during the impact process and allow for unique contact dynamics. Volatility was controlled by varying the acetone concentration in isopropanol mixtures (O(1 - 10 kPa) to keep surface tension relatively constant while the vapor pressure and viscosity increased. Nucleation onset was tracked using a high-speed optical total internal reflection microscopy (TIRM) technique where an increase in the vapor pressure enhanced wetting onset (i.e., pure acetone). However, the concentrations between 49 - 66% isopropanol which have vapor pressures of kPa, respectively, caused droplets to rebound at We up to We 21, beyond the classic disjoining pressure dominant regime of We > 10.