Why direct or reversed Hofmeister series? Interplay of hydration, non-electrostatic potentials, and ion size
D F Parsons1, M Boström, T J Maceina
1Research School of Physical Sciences and Engineering, Australian National University, Canberra, ACT 0200, Australia. Drew.Parsons@anu.edu.au
Abstract:
A modified Poisson-Boltzmann analysis is made of the double layer interaction between two silica surfaces and two alumina surfaces in chloride electrolyte. The analysis incorporates nonelectrostatic ion-surface dispersion interactions based on ab initio ionic excess polarizabilities with finite ion sizes. A hydration model for the tightly held hydration shell of kosmotropic ions is introduced. A direct Hofmeister series (K > Na > Li) is found at the silica surface while the reversed series (Li > Na > K) is found at alumina, bringing theory in line with experiment for the first time. Calculations with unhydrated ions also suggest that surface-induced dehydration may be occurring at the alumina surface.
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