Behaviour of hydrogen bonding and structure of poly(acrylic acid) in water–ethanol solution investigated by explicit ion molecular dynamics simulations

Molecular dynamics simulations of polyelectrolyte poly(acrylic acid) at infinitely dilute conditions in aqueous solutions containing up to 6 vol% ethanol were performed with explicit solvent and counter-ion description for varying degree of neutralisation. In the range of ethanol concentration employed, this study shows a swelling in the case of non-ionised chain, chain collapse for 25% ionised system, minimal swelling for 50% ionised chain and no significant change in conformation for 75–100% ionised chains. Ethanol interacts with non-ionised residues via hydrogen bonding and is found to be dominant in the solvation cage surrounding them, whereas no such interaction is seen with ionised residues. Thus, chains with higher charge densities show a preference for the aqueous environment in comparison to ethanol and hydrogen bonding to water is unaltered. For chains with lower charge density, a reduction in the hydrogen bonding with water is seen with an increase in ethanol concentration.