ABSTRACT
Intermolecular structure, hydration and conformations of Poly(vinylamine) (PVAm) in neutral as well as protonated (cationic) condition as polyelectrolyte in dilute aqueous solution, were studied via single-chain atomistic molecular dynamics simulations in explicit solvent. A parametric study of atomic partial charges was carried out at different values of degree-of-ionisation (f) of the amine group. A modification of generic GROMOS force-field is developed. The unusual non-monotonic behaviour of radius-of-gyration with an increase in f is captured, in agreement with experimental results of intrinsic viscosity. Cooperative solvation of PVAm chain occurs with an increase in f as assisted by counter-ion condensation. Three different regimes of the variation of radius-of-gyration of PVAm with change in f are identified. Changes in polymer-water hydrogen bonding is not the dominant effect for the behaviour of chain-size variation. The non-monotonous expansion of PVAm is attributed to the complex interplay between hydrogen bonding and intermolecular structure of polymer chain, water and counter-ions, all of which provide a cooperative solvation of the chain. With an increase in f at the higher range, the formation of ion pairs produces salt-bridges and bends in the chain, as well as ion-pair–ion-pair repulsion extending the chain at complete ionisation.
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