Transport properties of water in hydroxypropyl methylcellulose

The relation between the self-diffusion coefficient, Dself, of water and the free volume hole size, Vh, has been investigated in a hydroxypropyl methylcellulose (HPMC)–water system in the water content range 0.08–0.36 w/w, at room temperature. Furthermore, the thermal properties of the water in the HPMC–water system, as measured with differential scanning calorimetry (DSC) and the tensile storage, E′, and tensile loss, E″, moduli, of the HPMC–water systems, as determined with dynamic mechanical analysis (DMA), have been probed. Pulsed-field gradient nuclear magnetic resonance (PFG NMR) was used to measure the Dself of water and positron annihilation lifetime spectroscopy (PALS) was used to measure the ortho-Positronium (o-Ps) lifetime in the HPMC–water system. The glass transition temperature of the HPMC was found to be reduced by the water to room temperature in the water content range 0.10–0.15 w/w. The relation between ln Dself of water and the inverse free volume hole size of the HPMC–water system was non-linear. Furthermore, the PALS measurements showed that molecular water co-existed with water clusters in the HPMC–water system.