LAUSR

Clay minerals play important roles in myriad natural phenomena and engineered systems, from earthquakes and mudslides to barriers for nuclear waste storage and as caprocks for anthropogenic carbon sequestration. Swelling clays are especially important, with complex behavior that arises from the competing interactions between the layers. These include the electrostatic forces originating from heterovalent substitutions that create permanent negative charge within the layers, and the positively charged cations that intercalate between the layers. Predicting the response of swelling clays to changing environmental conditions, specifically ionic strength, remains a challenge due to the incomplete knowledge of clay layer structures and the roles of substitutions and defects at the single-layer limit. Here, we present new observations of clay layer structure at the atomic scale and new studies of the pathway for expansion or collapse under rapid changes in aqueous chemistry.