Molecular Dynamics Simulation of the Influence of Temperature and Salt on the Dynamic Hydration Layer in a Model Polyzwitterionic Polymer PAEDAPS

JA Clark and VM Prabhu and JF Douglas, JOURNAL OF PHYSICAL CHEMISTRY B, 127, 8185-8198 (2023).

DOI: 10.1021/acs.jpcb.3c03654

We investigate the hydration of poly(3-2-(acrylamido) ethyldimethylammonio propanesulfonate) over a range of temperatures in pure water and with the inclusion of 0.1 mol/L NaCl using atomistic molecular dynamics simulation. Drawing on concepts drawn from the field of glass-forming liquids, we use the Debye-Waller parameter () for describing the water mobility gradient around the polybetaine backbone extending to an overall distance approximate to 18 angstrom. The water mobility in this layer is defined through the mean-square water molecule displacement at a time on the order of water's ss-relaxation time. The brushlike topology of polybetaines leads to two regions in the dynamic hydration layer. The inner region of approximate to 10.5 angstrom is explored by pendant group conformational motions, and the outer region of approximate to 7.5 angstrom represents an extended layer of reduced water mobility relative to bulk water. The dynamic hydration layer extends far beyond the static hydration layer, adjacent to the polymer.

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