MONTE-CARLO SIMULATIONS OF A SINGLE POLY(OXYETHYLENE) C12E2 CHAIN HEADGROUP FIXED ON A BILAYER SURFACE IN WATER

Monte Carlo simulations of a single poly(oxyethylene) C-12E2 surfactan t chain headgroup attached to the hydrophobic wall of a bilayer have b een performed at various temperatures. The structure of the water arou nd the chain was examined by collecting radial distribution functions and densities for different regions in the plane of the bilayer surfac e. There is a strong tendency for water to form H-bonded 'bridges' bet ween adjacent oxygen atoms on the same chain and to favour gauche conf ormations for the O-C-C-O torsional angles, the effect being weaker th e higher the temperature. Water molecules have a weaker tendency to fo rm bridges between non-adjacent oxygen atoms within the chain. The obs erved gauche/trans ratio increase and stronger chain adsorption which are found with increasing temperature were explained by relatively wea ker water-chain interactions and a more dominant chain-wall interactio n at higher temperatures.