Publications

We employed dielectric spectroscopy to analyze charge conduction, glass transition temperature, and relaxation dynamics in six alginate (Alg) samples at low temperature. All underwent vitrification of a hydrated amorphous fraction: the as-stored Na-Alg powder at 220 K, the temperature-quenched Ca-Alg hydrogel and xerogel at 212 K, the frozen Na-Alg solution and the Na-Alg exposed to water-vapor saturated atmosphere at 194 K, and the slowly cooled hydrogel at 170 K. All samples displayed a Johari-Goldstein relaxation, and three of them displayed a structural relaxation; both processes originated from coupled Alg-H2O motions in the hydrated amorphous fraction. Charge conduction in all samples was dominated by Grotthuss proton shuttling (either in bulk water/ice or in hydration layers). H2O-rich samples displayed the H-bond network relaxation of ice, with an activation energy between 25 and 31 kJ mol-1, close to the energy of formation of one H-bond per H2O molecule. This relaxation was faster in the quenched hydrogel than in the slowly crystallized hydrogel and the frozen solution, likely due to a smaller average size of ice domains in the former; the latter samples display two separate ice relaxations, likely due to ionic impurities in the ice domains in contact with the Alg chains. The Na-Alg powder equilibrated in a water-vapor saturated atmosphere also displayed the local relaxation of bulk-like amorphous water with an activation energy of 51 kJ mol-1, equivalent to two H-bonds per H2O molecule. Most samples displayed spectral changes between 260 and 270 K due to ice melting. In the fast-quenched hydrogel, a premelting transition was observed at 220 K.

JTD Keywords: Absorption, Behavior, Dielectric-relaxation, Diffusion, Dispersion, Ice, Liqui, Nm pores, Spectra, Water