Monte Carlo simulations of a single poly(oxyethylene) C12E2 chain headgroup fixed on a bilayer surface in water

Abstract

Monte Carlo simulations of a single poly(oxyethylene) C₁₂E₂ surfactant chain headgroup attached to the hydrophobic wall of a bilayer have been performed at various temperatures. The structure of the water around the chain was examined by collecting radial distribution functions and densities for different regions in the plane of the bilayer surface. There is a strong tendency for water to form H-bonded ‘bridges’ between adjacent oxygen atoms on the same chain and to favour gauche conformations for the O—C—C—O torsional angles, the effect being weaker the higher the temperature. Water molecules have a weaker tendency to form bridges between non-adjacent oxygen atoms within the chain. The observed gauche/trans ratio increase and stronger chain adsorption which are found with increasing temperature were explained by relatively weaker water–chain interactions and a more dominant chain–wall interaction at higher temperatures.