Molecular Dynamics Study on the Heat of Phase Transition of Chloroacetate from the Bulk to the Surface Phases

Based on the surface adsorption theory developed in our group and molecular dynamics simulations, the adsorption behaviors of methyl chloroacetate, ethyl chloroacetate, propyl chloroacetate, methyl dichloroacetate, and methyl trichloroacetate at the vapor-liquid interface have been thoroughly investigated. The surface layer thickness of these five liquids shows a significant increase as temperature increases, but it decreases significantly with the increase of intermolecular interactions of chloroacetates. It is found with our surface adsorption theory that the reversible heat of phase transition for chloroacetates from bulk phase to surface phase increases from methyl chloroacetate to propyl chloroacetate with the alkyl chain and also increases from methyl chloroacetate to methyl trichloroacetate as the number of chloro group increases. Molecular dynamics simulation is exploited to calculate the entropies of these five liquids in the surface and bulk regions at various temperatures. The variation trends of the simulated results are consistent with those of the phase transition heats determined with our surface adsorption theory.