The thermodynamics of confined water and other stories

DAMIAN A SCHERLIS

Trieste

Seminario; Informal seminar on Chemical Physics; 2015

ICTP - International Center for Theoretical Physics

Classical thermodynamics is assumed to be valid up to a certain length-scale, below which the discontinuous nature of matter becomes manifest, and the macroscopic theory breaks down. This is the so called thermodynamic limit. In this seminar we will present results for the vapor pressure and contact angle of water in different nano environments, obtained from canonical and grand canonical molecular dynamics simulations, showing that the applicability of the master thermodynamic equations extends to unexpectedly small lengths, of only 1 or 2 nm.In particular, we will focus on the hydrophobicity of chemically heterogeneous surfaces, consisting of binary mixtures of hydrophilic and hydrophobic particles. The combination gives rise to a linear dependence of hydrophobicity with respect to composition, in agreement with the thermodynamic Cassie model. When the length-scale of the heterogeneity reaches the molecular dimensions, however, unprecedented deviations from linearity occur, and the hydrophobicity of the mixture may exceed that of the  pure hydrophobic component.