Anomalous [`]Freezing' of water in hydrophilic polymeric structures

Experiments, intended to establish the use of hydrophilic polymeric materials as vehicles for water in energy-storage devices, have revealed two anomalous effects during the freezing/melting phase-changes: 1. (1) the presence of a large difference between the temperatures at which latent heat is taken in, and at which the energy is evolved, i.e. a hysteresis effect in the phase changes exceeding 20°C under some circumstances; and 2. (2) a wide variation in the magnitude of the thermal energy stored per unit mass of the hydrated sample (i.e. of the apparent latent heat of the absorbed water), which varies with the type of hydrophilic polymeric material used, and depends in particular upon the [`]free moisture' content of the structure. These effects suggest that the hydrophilic polymeric structure inhibits the normal freezing process, either by mechanically interfering with the formation of a conventional ice-crystal structure, or by chemically immobilising some of the water molecules present in the system by transiently bonding them to hydrophilic sites within the polymer.