(393ax) Liquid Ethanol Simulated On Crystalline Alpha Alumina

Equilibrium molecular dynamics simulations were employed to investigate the structural properties of interfacial ethanol molecules on two alumina surfaces – the (0001) and the (102) terminations of a-Al­₂O₃ – both described using the CLAYFF force field. The results were quantified in terms of density profiles in the direction perpendicular to the substrate as well as along planes parallel to the substrate, in-plane radial distribution functions, residence times in contact with the substrate, orientational distribution functions for the methyl and the OH groups of ethanol, and reorientation autocorrelation functions. The density profiles show that ethanol molecules in the first monolayer have a well-organized arrangement reminiscent of the structure of the substrates. The orientation distribution in the second layer is rather broad and similar to that observed in the bulk. On the contrary, significant orientational order is observed within the first adsorbed layer, in which case the orientational distribution obtained for the methyl group of ethanol on a-Al­₂O₃(102) by our simulations is comparable to experimental results by Shen et al. [J. Phys. Chem. Lett. 2, 1831 (2011)]. Complementing experimental observations, our simulations show long residence times and slowly decaying reorientation autocorrelation functions for ethanol molecules in the first adsorbed layer, suggesting that these molecules are strongly coordinated with both a-Al­₂O₃ (0001) and a-Al­₂O₃(102) surfaces.