Estimation of Critical Temperature of Nano-Confined Alkanes using Vapour-Liquid Interfacial free Energy

Abstract

The critical temperature of bulk and confined alkanes are investigated making use of vapour-liquid interfacial free energy of coexistence received from grand-canonical transition matrix Monte Carlo simulations utilizing a histogram reweighting technique. For a system underneath investigation the temperature equivalent to zero interfacial free energy of coexistence is the estimated critical temperature. The acquired critical temperatures have revealed nonlinear monotonic tendency with converse of slit width. Moreover, four to five different linear regimes of critical temperature are observed in the studied series of slit width. In this work, Buckingham exponential-6 potential model is used to depict the interaction between alkane’s molecules and Steele potential is used for the interaction between confining surface (Graphite/Mica) and alkane molecules. In this investigation methane, n-butane and n-octane are subjected under graphite and mica slit pores of varying slit width. In case of methane; graphite slit width varied from 40 Å to 5.4 Å and mica slit width varied from 40 Å to 5 Å, for n-butane; graphite slit width varied from 40 Å to 5.8 Å and mica slit width varied from 40 Å to 5.5 Å, for n-octane; graphite slit width varied from 50 Å to 7 Å and mica slit width varied from 50 Å to 6.5 Å. This investigation additionally reveals that the critical temperature of bulk and confined alkane estimated using the vapour-liquid interfacial free energy of coexistence is within logical accuracy with that obtained using the simplified form of scaling law.