Electrostriction in Aqueous Solutions of Electrolytes

Abstract

A theory of electrostriction of solvent water near ions is developed. The treatment is based on a calculation of the effective pressure which would, in the absence of the field, cause the same change in volume as the field. The change in solvent volume near ions can be related, using an appropriate molecular model, to the apparent change in the volume of the salt upon dissolution. It is shown that the electrostriction arises at small ions mainly on account of changes of effective volume of the solvent rather than from compression of the ion cavity in the dielectric. This treatment avoids the difficulties of previous calculations where use of the Born equation involves an integration over a distance from the ion. The calculations also lead to information on the local compressibility of solvent water in regions near ions and provide a better basis for interpretation of compressibility measurements in terms of ionic hydration. Explicit approximate solutions for high‐ and low‐field conditions, and a complete numerical solution for the effective pressure—field relation are given.