Intramolecular and lattice melting in n-alkane monolayers: An analog of melting in lipid bilayers

Molecular dynamics (MD) simulations and neutron diffraction experiments have been performed on n-dotriacontane (n-C₃₂D₆₆) monolayers adsorbed on a graphite basal-plane surface. The diffraction experiments show little change in the crystalline monolayer structure up to a temperature of ∼350 K above which a large thermal expansion and decrease in coherence length occurs. The MD simulations provide evidence that this behavior is due to a phase transition in the monolayer in which intramolecular and translational order are lost simultaneously. This melting transition is qualitatively similar to the gel-to-fluid transition found in bilayer lipid membranes.