Interfaces of Propylene Carbonate

TL;DR

This study uses molecular dynamics simulations to analyze the wetting behavior, molecular structure, and thermodynamic properties of propylene carbonate on graphite, providing detailed insights into its interface characteristics.

Contribution

It offers new simulation-based insights into PC's contact angle, layering, molecular orientation, and thermodynamic properties, aligning well with experimental data.

Findings

Propylene carbonate wets graphite with a contact angle of 31 degrees.

Simulated nano-droplets show layering and pyramid structures.

Computed properties like thermal expansion and dielectric constants match experiments.

Abstract

Propylene carbonate (PC) wets graphite with a contact angle of 31 deg at ambient conditions. Molecular dynamics simulations agree with this contact angle after 40% reduction of the strength of graphite-C atom Lennard-Jones interactions with the solvent, relative to the models used initially. A simulated nano-scale PC droplet on graphite displays a pronounced layering tendency and an Aztex pyramid structure for the droplet. Extrapolation of the computed tensions of PC liquid-vapor interface estimates the critical temperature of PC accurately to about 3%. PC molecules lie flat on the PC liquid-vapor surface, and tend to project the propyl carbon toward the vapor phase. For close PC neighbors in liquid PC, an important packing motif stacks carbonate planes with the outer oxygen of one molecule snuggled into the positively charged propyl end of another molecule so that neighboring molecule dipole moments are approximately antiparallel. The calculated thermal expansion coefficient and the dielectric constants for liquid PC agree well with experiment. The distribution of PC molecule binding energies is closely Gaussian. Evaluation of the density of the coexisting vapor then permits estimation of the packing contribution to the PC chemical potential, and that contribution is about 2/3rds of the magnitude of the contributions due to attractive interactions, with opposite sign.