Smectite phase separation is driven by hydration-mediated interfacial charge

Michael L Whittaker; Mohammad Shoaib; Laura N Lammers; Yugang Zhang; Christophe Tournassat; Benjamin Gilbert

doi:10.1016/j.jcis.2023.05.085

Smectite phase separation is driven by hydration-mediated interfacial charge

J Colloid Interface Sci. 2023 Oct:647:406-420. doi: 10.1016/j.jcis.2023.05.085. Epub 2023 May 20.

Authors

Michael L Whittaker¹, Mohammad Shoaib², Laura N Lammers³, Yugang Zhang⁴, Christophe Tournassat⁵, Benjamin Gilbert⁶

Affiliations

¹ Energy Geosciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA; Department of Earth and Planetary Science, University of California, Berkeley, CA 94720, USA. Electronic address: mwhittaker@lbl.gov.
² Energy Geosciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA.
³ Energy Geosciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA; Department of Environmental Science, Policy and Management, University of California, Berkeley, CA 94720, USA.
⁴ Center for Functional Nanomaterials, Brookhaven National Laboratory, Upton, NY 11973, USA.
⁵ Energy Geosciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA; Institut des Sciences de la Terre d'Orléans, Université d'Orléans-CNRS-BRGM, Orléans 45071, France.
⁶ Energy Geosciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA; Department of Earth and Planetary Science, University of California, Berkeley, CA 94720, USA.

PMID: 37269737
DOI: 10.1016/j.jcis.2023.05.085

Abstract

Smectite clay minerals have an outsize impact on the response of clay-rich media to common stimuli, such as hydration and ion exchange, motivating extensive effort to understand behaviors resulting from these processes such as swelling and exfoliation. Smectites are common and historic systems for investigating colloidal and interfacial phenomena, with two swelling regimes commonly identified across myriad clays: osmotic swelling at high water activity and crystalline swelling at low water activity. However, no current swelling model seamlessly spans the full ranges of water, salt and clay content encountered in natural or engineered settings. Here, we show that structures previously rationalized as either osmotic or crystalline coexist as a rich array of distinct colloidal phases that differ by water content, layer stacking thickness, and curvature. We present an analytical model for intermolecular potentials among water, salt and clay in both mono- and divalent electrolytes that predicts swelling pressures across high and low water activities. Our results indicate that all clay swelling is osmotic swelling, but that the osmotic pressure of charged mineral interfaces becomes attractive and dominates that of the electrolyte at high clay activities. Global energy minima are often not reached on experimental timescales due to many local energy minima that promote long-lived intermediate states with vast differences in clay, ion, and water mobilities, leading to hyperdiffusive layer dynamics driven by variable hydration-mediated interfacial charge. Teaser Distinct colloidal phases of swelling clays emerge via ion (de)hydration at mineral interfaces that drives hyperdiffusive layer dynamics as metastable smectites approach equilibrium.