Effect of Added Salts on the Interfacial Dynamics of Monovalent Metal Ions and Model Water-Soluble Polymers

Soumik Ghosh; Jack F. Douglas; Francis W. Starr

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arXiv · 2610.04934

Effect of Added Salts on the Interfacial Dynamics of Monovalent Metal Ions and Model Water-Soluble Polymers

Soumik Ghosh·Jack F. Douglas·Francis W. Starr

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Abstract

Traditional theories of electrolyte and polyelectrolyte solutions overlook ion and polymer hydration, yielding an overly idealized perspective of the thermodynamic and dynamic properties of these solutions. In particular, the propensity of certain ions to increase or decrease the water diffusion coefficient at low solution concentrations, is poorly understood, a phenomenon that correlates strongly with the Hofmeister series describing the influence of salts on the solubility and self-assembly of synthetic and biomacromolecules as well as colloidal particles. These ion-specific effects have profound ramifications in diverse biological, medical science and technological applications. We address the general problem of understanding ion and uncharged water-soluble polymer hydration through molecular dynamics (MD) simulations of representative water-soluble polymers, polyacrylamide (PAM) and polyethylene oxide (PEO), in aqueous salt solutions. Careful attention is given to the capacity of our model to reproduce observed trends of added monovalent salts on the diffusion coefficient of water. Reproducing these ion-specific trends in the mobility of water has been a recurrent challenge in prior MD simulations of aqueous solutions based on a physically realistic model of water. Our work on salt solutions represents an important advance on which we build our modeling of aqueous polymer solutions with added salts. Simulations of our model polymers reveal an extended nanoscale dynamic hydration layer having a scale on the order of one nanometer (nm) in which the mobility is perturbed from its bulk value, and the mobility gradient in this layer appears to obey a near universal functional form.

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Soumik Ghosh, Jack F. Douglas, Francis W. Starr. 2026-10-04. Effect of Added Salts on the Interfacial Dynamics of Monovalent Metal Ions and Model Water-Soluble Polymers. https://arxiv.org/abs/2610.04934

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