Deciphering anomalous dielectric traits of nanoconfined water and its roles in modeling crystalline swelling of bentonite

The physicochemical properties of Na-montmorillonite (Na-Mt) determine the intrinsic behaviors of bentonite, which are of great significance for its application in high-level radioactive waste disposal. The dielectric behavior of water under nanoconfinement has been the subject of numerous conjectures due to the difficulties associated with experimental investigation. Na-Mt is modeled via molecular dynamics (MD) simulations at the nanoscale, and the dielectric responses as a function of the basal spacing and water density are studied. The results showed a heterogeneous dielectric profile of interlayer water and an unexpected local dielectric enhancement closed to Mt surface. The morphological characteristics of dielectric constant (\(\upvarepsilon\)) was consistent with the layered structure of interlayer water. The hydrogen bonding network was strengthened near the interface, resulting in a local density augmentation and dipolar mobility decline of interlayer water. This anomalous dielectric behavior was mainly derived from the interfacial effect, rather than the physical field in Na-Mt interlayer. Introducing the MD simulations results into crystalline swelling model, and a significant improvement in accuracy was observed. These results provide a clear insight into the dielectric behavior of interlayer water in Na-Mt.