Temperature Dependence in Heterogeneous Nucleation with Application to the Direct Determination of Cluster Energy on Nearly Molecular Scale

Description

This poster presents a synopsis of findings from a recent Nature publication (McGraw et al., 2017). An analysis of temperature-dependent heterogeneous nucleation of water vapor on nanoparticles is presented and shown to provide the energy of critical cluster formation as well as several other microscopic properties of the critical cluster, including its size, directly from measurements of nucleation probability. Temperature dependence is correlated with cluster stabilization by the nanoparticle seed and previously found cases of unusual increasing nucleation onset saturation ratio with increasing temperature are explained. A necessary condition for the unusual positive temperature dependence is identified, namely that the critical cluster be more stable, on a per molecule basis, than the bulk liquid to exhibit the effect. Temperature dependence is next examined in the classical Fletcher model, modified here to predict cluster energies. The contact angle used in the Fletcher model is identified as the microscopic contact angle, which can be directly obtained from heterogeneous nucleation experimental data by a recently developed analysis method. Here an equivalent condition, increasing contact angle with temperature, is found necessary for occurrence of unusual temperature dependence. Our findings have immediate applications to atmospheric particle formation and to technologies for nanoparticle detection using condensation particle counters (CPCs). Reference: R. L. McGraw, P. M. Winkler & P.E. Wagner (2017). Scientific Reports 7, 16896.