Transition Mechanisms and Phases of Hexane Physisorbed on Graphite

We present the results of molecular dynamics (MD) simulations of hexane adsorbed onto graphite at submono-layer (ρ<1), monolayer (ρ=1), and supermonolayer (ρ>1) coverages. We find the presence of three phases, the low temperature solid herringbone (HB) phase, the inter-mediate-nematic (IN) phase, and the isotropic fluid phase. For submonolayer coverages, we find that the IN phase disappears except for coverages very close to completion, however, for ρ>1 we find an augmented IN phase with most molecules rolled normal to the substrate. We also observe for ρ<1 the presence of fluid-filled domain walls when taking the tetrahedral symmetry of the endgroups into account. Through variations we study the formation of gauche molecules and conclude that both phase transitions observed exhibit much out-of-plane tilting, with only a small presence of conformation changes near the melting transition. We conclude that in-plane space plays an important role in the phases and transitions in this system