Molecular dynamics simulation and thermodynamic model of triple point of Lennard-Jones fluid in cylindrical nanopores

Abstract Triple points of a Lennard-Jones (LJ) fluid in cylindrical nanopores were examined using molecular dynamics simulations. At higher temperatures, the LJ fluid was capillary-condensed and was in equilibrium with the vapour phase in the pore space. The freezing of capillary condensates in cylindrical nanopores upon cooling represented phase transitions from vapour–liquid coexistence to vapour–solid coexistence, which occurred at the triple point in the cylindrical nanopores. The triple-point pressures in the cylindrical nanopores were approximately one order of magnitude lower than those in the bulk. The triple-point temperatures in the cylindrical nanopores were not inversely proportional to the pore size. The intersection of the thermodynamic models of vapour–liquid and solid–liquid coexistence previously derived by the authors can represent the state of vapour–liquid–solid coexistence. The thermodynamic triple-point model in cylindrical nanopores was successfully used to predict the molecular dynamics in nanopores.