High-Resolution Volumetric Adsorption and Molecular Dynamics of then-Alkanes on the Surface of Hexagonal Boron Nitride

Abstract

High-resolution, volumetric adsorption isotherm measurements of methane through octane on hexagonal boron nitride (hBN) were performed in the vicinity of their bulk triple-point temperatures. It is observed that the adsorption behavior can be classified into three regimes depending on the molecular geometry and chain length; i.e., quasispherical, cigarlike, and rodlike. The film growth is observed to change from six discrete steps, i.e., layer-by-layer like, to two discrete steps, i.e., incomplete wetting as the molecular length increases. The heat of adsorption and differential entropy and enthalpy were calculated from these isotherm data for monolayer, bilayer, and where possible, thicker films. It is found that the monolayer heat of adsorption exhibits a smooth increase with increasing chain length. Molecular dynamics simulations were performed to provide complementary microscopic insight into the adsorption properties of these alkanes on hBN. Concentration profiles (C(z)) normal to the hBN surface pla...