Molecular Simulation of Critical Parameters of Nano-Confined n-Alkanes

TraPPE force field combined with grand-canonical transition-matrix Monte Carlo simulation were used to investigate the vapor-liquid coexistence curve and critical properties of methane, ethane, propane, and n-butane in slit pores ranging from 6 ? to 40 ?. Long range correction for intermolecular potential in slit pore model was developed, and the fact indicating that its influence on various thermodynamic properties is not negligible was found. The simulation results show that the thermodynamic properties of nano-confined alkanes shift tremendously from the bulk state. The critical temperature under confinement experiences a roughly linear decrease with an inverse in the slit width, while the critical pressure and the critical density have a relative increment related with carbon number on both the large slit width region and the small slit width region. Further analysis on z-density profiles of alkanes revealed that the complex behaviors of shift in critical parameters are the results of interplay between fluid-fluid and fluid-wall interaction.