Study of the molecular mobility of polysaccharide solid thin layers by dielectric relaxation spectroscopy

Temperature dependence of measured dielectric relaxation spectra (DRS) in the frequency range 20 Hz - 1 MHz of hydroxyethylcellulose (HEC) are in the temperature range 100 - 350 K of Arrhenius character with one relaxation process at 150 - 250 K. This process reflects most probably beta-relaxation of the side chain groups. Calculated activation energy of this process was 5730 kJ/mole. Four types of polysaccharides were studied at 293 K temperature: hyaluronic acid (HA), chondroitin sulfate (CHS), HEC and carboxymethylcellulose (CMC), in the low-frequency range 10(-5) - 10(0) Hz. Measured dielectric spectra were interpreted as sum of one A.C. conductivity process and of up to two relaxation processes. The relaxation processes were described by means of the Havriliak-Negami formula and their parameters were related to the molecular structure of the polymers. The low value of ct in CHS is related to its strong coupling due to the presence of two polar groups in its monomeric unit, whereas low values of alpha x beta are interpreted as being due to the strong steric hindrances caused by long pendants present in HEC.