Interfacial Properties of Model Systems Using Isothermal Isobaric Monte Carlo Simulations

The behavior of fluids at solid surfaces plays a significant role within numerous natural phenomena and industrial applications. To this end, understanding and predicting the interfacial properties of these systems is crucial for the development of emerging technologies. Within our group, we have developed an interface potential based approach for determining interfacial properties. Within our previous efforts, this approach has been implemented within the grand canonical ensemble. However, there are limitations to working within this ensemble, particularly when applying the techniques to complex molecules and working at relatively low temperature. In this presentation, we introduce a means to overcome these limitations. We use a free energy based approach in which Monte Carlo simulations are performed to obtain interface potential by growing a liquid or vapor film on the solid substrate. Isothermal Isobaric ensemble (NPT) Monte Carlo simulation is employed within a “spreading” and “drying” framework to calculate the wetting properties, such as the spreading coefficient, contact angle, and, interfacial tension. Expanded Ensemble techniques are used to evaluate these interfacial properties over a range of temperatures and substrate strengths. We also show how to reduce computational expense of volume moves in NPT Monte Carlo simulation. Results are presented for a model system consisting of fluid-fluid interactions described by Lennard-Jones potential. We also show results for the SPC/E water model at a structureless 9-3 surface over a range of substrate strengths and temperatures. The results obtained for these model systems using NPT Monte Carlo method are compared with results obtained from GCMC simulations.