NMR investigation of the porosity of hypercrosslinked polystyrene and the properties of water confined in its nanopores

The melting of water frozen preliminarily at 180 K in a free internal volume of water-swollen hypercrosslinked polystyrene networks with degrees of crosslinking ranging from 43 to 500% is studied by NMR. It is found that ice melts within a narrow range of low temperatures, 195-225 K, demonstrating that the pores in the networks are small and uniform in size. It is, however, impossible to calculate the pore size via the Gibbs-Thomson equation, since the structure of water (and hence its properties) depend on a sample's rate of freezing. We conclude that the activation of the orientational motions of water molecules starts to manifest itself already at 200 K; upon reaching 220-230 K, the total mobility of water molecules is due largely to translational motions with an activation energy of 27-28 kJ/mol.