Molecular Dynamics Study of Water Interacting with Siloxane Surface Modified by Poly(ethylene oxide) Chains

Abstract

In this work, static and dynamic properties of interfacial water molecules on the amorphous siloxane surface covered by poly(ethylene oxide) (PEO) chains grafted at different coverage densities σ were studied using atomistic molecular dynamics simulations. It is shown that water molecules compete with the ethylene oxide (EO) monomers for interaction sites on the siloxane surface and for the space above it. Two types of orientations of the water molecules are identified as the most populated: one with the dipole moment vector pointing toward the siloxane surface and another with the dipole moment vector pointing about 5° away from the surface. In both the hydrogen pair is amenable to rotate around the dipolar axis. The higher the coverage density the larger the disorder of water molecules, but the dipole moment-down orientation still dominates. The number of water–water hydrogen bonds monotonically decreases with σ, whereas the number of water–PEO hydrogen bonds displays a maximum around the crossover to t...