Water dynamics in Evaporating Nanodroplets

The evaporation of droplets on heated substrates has been intensively studied in the last several decades. As such, well validdated continuum theories have been developed that describe the modes of evaporation, evaporating profiles, and also predict the internal convective flows compatible with the evaporating modes. The evaporation of small nanoscale droplets plays a key role in a myriad of scientific and technological applications from atmospheric chemistry to the cooling of nanoelectronics to catalysis, where evaporating nanodroplets produced by electro spray ionization are increasingly being used to accelerate chemical reactions. At the nanoscale, however, where large surface to volume ratios govern the behavior, and fluctuations play a major role, it remains unclear whether the continuum theories can be applied to predict the the response. Here, we put that to the test and use classical molecular dynamics simulations of water nanodroplets of two different sizes both suspended under isothermal evaporation conditions and on heated substrates with different levels of hydrophobicity. We focus on mapping the convective flows that develop within water nanodroplets and the resulting evaporating profiles, with the aim of assessing the predictive power of the continuum theories.