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 are 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 many variables such as the enthalpy of vaporization, the superheat, the 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 a normal temperature and pressure 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. Wetting onset was tracked using a high-speed optical total internal reflection microscopy technique where an increase in the vapor pressure enhanced wetting onset (i.e., pure acetone). However, the concentrations between ≈ 49% and 66% isopropanol, which have vapor pressures of ≈11.3–14.8 kPa, respectively, caused drops to rebound at We up to We ≈ 21, beyond the classic disjoining pressure dominant regime of We > 10.