Counterion-dependent Dynamics of Nanoconfined Water in Lyotropic Liquid Crystalline Mesophases

Understanding how the interfacial chemical functionalities influence nanoconfined water dynamics could potentially inform the design of next-generation permselective and ion-transporting membranes for energy applications. However, lacking access to well-defined systems with tunable interfacial chemistries and nanoconfinement geometries has hampered conclusive studies of water dynamics therein. Derived from the water concentration-dependent self-assembly of small molecule surfactants, lyotropic liquid crystals (LLCs) offer a platform for studying confined water dynamics in nanopores (diameters ~0.7-2.5 nm) lined with well-defined chemical functionalities. In this contribution, we describe the synthesis and aqueous phase behavior of ionic gemini dicarboxylate surfactants, which form technologically-useful, normal double gyroid phases in which water is nanoconfined between two carboxylate-lined, convex interfaces. Quasielastic neutron scattering (QENS) measurements indicate that the gyroid water dynamics are significantly slower than in bulk water, and that the observed dynamics are very sensitive to the nature of the charge-compensating counterion (Na⁺, K⁺, Me₄N⁺) associated with the carboxylate surfactant headgroup.