Dynamical conductivity of confined water

The electrodynamic response of water confined in nanoporous MCM-41 is measured in the frequency range 1 MHz–3 THz at room temperature. The results are analyzed in the context of a recently proposed ionic model of water. We found an increase in dc-conductivity of confined water by 3 orders of magnitude (3.3 10−3 Ω−1 m−1) compared to bulk water (5.5 10−6 Ω−1 m−1). This is attributed to the increase of H3O+ and OH− ion mobility, due to a decrease of the effective potential amplitude by walls of the confining environment. We found that the absorption in the microwave frequency range is much smaller in the medium with confined water than in the bulk water, and the quadratic dependence of the conductivity (σ) on frequency (ω) becomes less steep and tends to σ ~ ω. The results are of fundamental importance and can be used for understanding of the proton transport in systems with water in the nanoconfined state.