Molecular dynamics study of the volumetric and hydrophobic properties of the amphiphilic molecule C8E6

A correlation between volumetric properties and hydrophobicity of the surfactant molecule hexaethylene glycol monooctyl ether (С8Е6) in aqueous solution is studied. Molecular dynamic models of a single С8Е6 molecule surrounded by 7075 water molecules were simulated and analyzed for different temperatures at ambient pressure. The apparent volume (Vapp) of the solute molecule was calculated. The intrinsic volume of the solute molecule (Vint) was defined as the volume of the Voronoi region of the solute molecule (calculated on the basis of power (radical) Voronoi tessellation). It is shown that the contribution of the hydration water to the apparent volume (ΔV = Vapp − Vint) is negative for lower temperatures and becomes positive for higher temperatures. The degree of hydrophobicity of С8Е6 was also calculated by two different methods. It was shown that the solute molecule is hydrophilic at lower temperatures and becomes hydrophobic with temperature increase. This change occurs at a temperature which coincides well with the temperature, where the volumetric characteristic ΔV changes its sign.