Molecular Dynamics Study of Polymer−Water Interaction in Hydrogels. 2. Hydrogen-Bond Dynamics

Molecular dynamics simulations have been performed for hydrogel models of poly(vinyl alcohol) (PVA), poly(vinyl methyl ether) (PVME), and poly(N-isopropylacrylamide) (PNiPAM). The dynamics of hydrogen bonds and the translational and rotational motions of water molecules in the vicinity of the polymer segments are analyzed to investigate the properties of water molecules which are highly cooperative with the surrounding polymer chains. The characters of the hydrophilic groups which are reflected in the lifetime of hydrogen bonds, the spectral density, etc., are examined. The mobility of water molecules is significantly lowered around polymer chains for both translational and rotational motions. This is partly because of the hydrogen bonds between water and polymers around the hydrophilic groups and partly because of the structuralization of water around the hydrophobic groups.