Comparison of measurement techniques for the identification of bound water restrained by polymers

We attempted to compare the measurement methods concerning characterization of bound water restrained by hydrophilic polymers having biocompatibility, since the structural change of water on the surface of bio-membranes has attracted considerable attentions. In particular, calorimetry that has been used for quantitative analysis of bound water in bio-membranes has been criticised in terms of the results obtained by nuclear magnetic resonance spectrometry, infrared/Raman spectrometry, X-ray analysis, and neutron scattering measurements. Based on the identical definition of bound water, and by using biocompatible polymers, the present status of calorimetry is investigated in order to identify and quantify the bound water restrained by bio-membranes.

Research highlights
► Non-freezing water, freezing bound water and free water are observed in water-biopolymer systems by DSC.
► Non-freezing water is directly restrained by the hydrophilic group of biopolymers.
► Ice-melting of freezing bound water is observed at a temperature lower than 0 °C.
► Ice of freezing bound water is in non-equilibrium state.