Poly(oxyethylene)-water interactions: A molecular dynamics study

Molecular dynamics simulations of a poly(oxyethylene) (POE) chain with 15 ethylene oxide (EO) units have been performed in an aqueous solution for 2 ns at 300 K and for 1 ns at 373 K, a cloud point for POE. The conformation and the hydration structure of POE and the structure and the dynamics of water molecules in the vicinity of POE were examined. The conformation of POE was transformed from a collapsed chain in the gas phase to a helix in water which was maintained for 2 ns. After a simulated annealing at 1000 K, POE still showed a preference for a helix. An extended network of POE-water and water-water hydrogen bonds was found throughout inside the helix, stabilizing the helix backbone. The same helical conformation was maintained even at 373 K. The pair distribution functions for water oxygen atoms near POE indicated significantly enhanced water structures in the hydrophilic region of POE, and to a lesser extent in the hydrophobic region, at both 300 and 373 K. Considerably reduced translational movements of water molecules near POE were also observed at both temperatures. All the results obtained from the simulation are in good agreement with experiments. We discuss the solubility and the phase behavior of POE in water, based on the observation from the simulations.