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 ( \(\upvarepsilon\) $\mathrm{\epsilon }$ ) 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.