(484d) Statistical Mechanics of Fluids At Interfaces and Under Confinement Via Mayer-Sampling Monte Carlo Simulation

The physical properties of small systems are fundamental importance in many industrial fields, such as membrane separation, oil recovery and colloidal stability. Engineering such processes requires molecular understanding of interfacial or confined systems. The study of surface phenomena is far less well developed compared to a vast knowledge of the phase behavior of infinitely large systems. When a system volume is reduced to micro/nano-size level, the physical properties are no longer size independent.  Experiments and molecular simulations show that a confined fluid behaves differently from the corresponding bulk fluid. A finite system of interacting molecules itself makes the interaction on a given molecule different. In the present work, we study the effect of surface fluid interaction on the thermodynamic properties of simple fluids in slit pores using cluster expansion methods. The relevant surface variables for simple fluids confined in slit pores are directly expressed in terms of molecular interactions. The Mayer-sampling Monte Carlo (MSMC) method is applied to calculate the necessary cluster integrals which contains surface contributions. MSMC is a general technique for evaluation of the integrals appearing in the expression for the virial coefficients, using ideas from free-energy calculations. We report the results of calculation of surface cluster integrals evaluated by using MSMC. These results are used to obtain critical data under confinement, even close to molecular diameters . Also we discuss the behavior of the surface virial coefficients as varying slit width and surface fluid interaction strength. Finally we analyze the influence of finite size on the phase transition, shift of the critical point, and critical temperatures predicted by surface virial equation of state for confined fluids through molecular clustering.