Dielectric study on non-equilibrium relaxation dynamics of the protic ionic liquid verapamil hydrochloride (VH) in nanopore-confinement☆

Non-equilibrium effects in confined geometry are characterized by various deviations from bulk behavior and have a limited lifetime. Understanding these phenomena is crucial for controlling material properties and optimizing their applications. In this study, by using dielectric spectroscopy, we investigated the conductivity relaxation dynamics and the equilibration kinetics of the protic ionic liquid (PIL, verapamil hydrochloride, VH) confined within anodic aluminum oxide (AAO) nanopores. Our results demonstrate that decreasing the pore diameter (from 160 nm to 20 nm) and annealing temperature, as well as larger temperature jumps ( Δ T ), lead to longer equilibration times. It has been shown that, at the initial stage of equilibration, ionic dynamics deviate significantly from bulk-like behavior. However, the confined system gradually recovers its ionic conductivity characterized for the bulk sample. We have also demonstrated that the equilibration process is closely linked to corresponding volume and pressure changes within the nanopores. Therefore, density fluctuations play a crucial role in equilibration kinetics under nanopore-confinement. Our findings provide fundamental insights into the design of stable nanomaterials based on PILs, with potential applications in electrochemical devices and pharmaceutical formulations.