Speaker
Description
Many soft and biological systems operate in ionic environments where salts significantly influence water transport and stability. In aqueous electrolyte solutions, viscosity and diffusivity are often described by the empirical Jones–Dole relation and commonly discussed in terms of structure-making (kosmotropic) or structure-breaking (chaotropic) ions [1]. However, the physical basis and the robustness of these trends remain subjects of debate. Therefore, we aim to develop a computationally efficient framework to capture these transport behaviors and extend the analysis to less-explored regimes with limited experimental data.We modify a cooperative coarse-grained water model, previously demonstrated to qualitatively reproduce key water anomalies [2], to include ionic effects in a mean-field manner without explicit ions. Ionic influences are incorporated through concentration-dependent changes in: (i) the directional hydrogen-bond interactions between water molecules and (ii) the effective volume associated with hydrogen-bond fluctuations, guided by experimental data [3]. Simulations are conducted within a Monte Carlo NPT ensemble, enabling efficient sampling and extraction of transport properties such as viscosity and diffusivity.The proposed framework qualitatively captures Jones–Dole-like trends in viscosity and diffusivity over a wide concentration range, including deviations at higher concentrations that are consistent with experimental findings. Extending the study to varying pressures reveals an asymmetric response: structure-making behavior remains stable across the conditions examined, while structure-breaking behavior becomes pressure-dependent, exhibiting a crossover at elevated pressures. In conclusion, the model successfully reproduces the key trends related to structure-making and structure-breaking ions, providing predictive insights even in regimes with sparse experimental data.
[1] Jones, G.; Dole, M. J. Am. Chem. Soc. 51 (1929) 2950–2964. DOI: 10.1021/ja01385a012.
[2] de los Santos, F.; Franzese, G. J. Phys. Chem. B 115 (2011) 14311–14320. DOI:
10.1021/jp206197t.
[3] Corridoni, T.; et al. J. Phys. Chem. B 115 (2011) 14008–14013. DOI: 10.1021/jp202755u.
