Use of dielectric spectroscopy to monitor molecular mobility in glassy and supercooled trehalose

Dielectric spectroscopy was used to comprehensively characterize the molecular mobility in amorphous trehalose, an extensively used bioprotective agent. Isothermal frequency sweeps were carried out at different temperatures in the glassy and supercooled liquid states of freeze-dried trehalose. Two previously reported secondary relaxations were observed at temperatures far below its glass transition temperature (T_g). At temperatures close to T_g, removal of dc conductivity contribution revealed a relaxation peak. The origin of this peak was evaluated using several diagnostic tests and determined to be the α-relaxation. There was also an excess wing in the high-frequency tail of α-relaxation. Sub-T_g annealing caused the primary relaxation to shift to lower frequencies, enabling resolution of the excess wing, which was characterized to be the true Johari-Goldstein (JG) relaxation. A qualitatively similar effect of annealing on JG relaxation was also observed. The average relaxation times of the two previously reported secondary relaxations were unaffected by annealing.