Phase Transition and Dynamics of Water Confined in Hydroxyethyl Copper Rubeanate Hydrate

This paper reports the results of the heat capacity (C-p) and quasi-elastic neutron scattering (QENS) measurements on hydroxyethyl copper rubeanate hydrate and its deuterated analogues. These materials accommodate water in their nano-pores and exhibit large proton conductivity at room temperature. The C-p data revealed that the adsorbed water gives rise to a glass transition and a first-order transition at 170 K and 260 K, respectively. The QENS data clarified that the adsorbed water consists of the free water apart from the pore wall and the bound water condensed on the pore wall. The diffusion coefficients of both waters are smaller than those of copper rubeanate hydrates owing to the steric hindrance caused by the hydroxyethyl group. The free water transforms to the condensed water through the transition at 260 K as in the case of copper rubeanate hydrates.