Dynamics of Water Near Oxidized Polystyrene Films Stela Andrea Muntean,* Roman A. Gerasimov, Alexey V. Lyulin 1. Introduction Water is the most important ingredient for the existence of life. And still, its structure and dynamics near the interfaces is not completely understood, and is object of vivid discussions in the scientific community. [1,2] In particular, when it comes to biological systems, the interactions between water and surfaces of biomolecules become crucial. Also the fact that interactions between biomole- cules is a water-intermediated process provides the motivation to study the behavior of water more carefully. A practical example is a biosensor, [3] where the interactions between the biomolecules to be detected and the solid phase of the biosensor, which for some applications is typically a polymeric surface, is intermediated by the water surrounding the biomolecule. The structure of water is mainly determined by the network of hydrogen bonds (HB) formed between water molecules. [4] Each water molecule is able to form between 0 and 4 hydrogen bonds. In liquid water, this network formation is not frozen, but is rather lively dynamic process, the hydrogen bonds are breaking and forming all the time. If a solute is placed in water, this will disturb the network of hydrogen bonds, giving rise to an effective interaction between water and the solute. The sign and the magnitude of this effective interaction is influenced by the nature of the solute, mainly its hydrophobic or hydrophilic character and by the size of the solute. The hydrophilic/hydrophobic character of the solute is determined by the chemical structure of its surface, in particular by the ability of Full Paper S. A. Muntean Theory of Polymers and Soft Matter (TPS), Department of Applied Physics, Eindhoven University of Technology, Den Dolech 2, 5600 MB Eindhoven, Netherlands E-mail: s.a.muntean@tue.nl S. A. Muntean Dutch Polymer Institute, P.O. Box 902, 5600 AX Eindhoven, Netherlands R. A. Gerasimov Department of Physics, Cherepovets State University, pr. Lunacharskogo 5, Cherepovets, Vologda region, 162600 Russia Alexey V. Lyulin Theory of Polymers and Soft Matter (TPS), Department of Applied Physics, Eindhoven University of Technology, Den Dolech 2, 5600 MB Eindhoven, Netherlands Atomistic MD simulations of water in the vicinity of oxidized amorphous atactic polystyrene are presented. The changes in the orientational and translational dynamics of water near polymer surfaces with different hydrophilicity are studied. Two main orientational relaxation processes of water molecules are distinguished: a process on a fs timescale, associated with the ballistic motion of water molecules, and a process on a ps timescale, associated with the self-diffusion of water. The fast process is not affected by the presence of the polymeric surface. The second relaxa- tion process differs at the interface from that in the bulk in that the dynamics of water molecules is more heterogeneous in the first. The effect of the representa- tion of polystyrene films on the water dynamics is discussed. ß 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim wileyonlinelibrary.com Macromol. Theory Simul. 2012, DOI: 10.1002/mats.201200025 1 Early View Publication; these are NOT the final page numbers, use DOI for citation !! R