Anomalous temperature behavior in clay swelling due to ion-ion correlations

¹ Theoretical Chemistry, Chemical Center - POB 124, S-221 00 Lund, Sweden
² Clay Technology AB, IDEON Research Center - S-223 70 Lund, Sweden

Received: 8 April 2016
Accepted: 12 May 2016

Abstract

We show, experimentally and theoretically, that swelling of both natural and refined clays has an anomalous temperature behavior depending on counterion valency. In an aqueous clay dispersion dominated by monovalent counterions the swelling pressure increases with temperature as expected from entropic arguments. In a clay with predominantly divalent counterions, the opposite behavior is found. The explanation is due to the fact that ion-ion correlations increase with temperature. Ion-ion correlations are important at strong electrostatic coupling and in an aqueous solution the dielectric permittivity, , drops with increased temperature, T, in such a way that the product also decreases. Thus, the net effect is an increased coupling.