Molecular Relaxation Behavior and Isothermal Crystallization above Glass Transition Temperature of Amorphous Hesperetin

The purpose of this paper was to investigate the relaxation behavior of amorphous hesperetin (HRN), using dielectric spectroscopy, and assessment of its crystallization kinetics above glass transition temperature (Tg). Amorphous HRN exhibited both local (β-) and global (α-) relaxations. β-Relaxation was observed below Tg, whereas α-relaxation prominently emerged above Tg. β-Relaxation was found to be of Johari-Goldstein type and was correlated with α-process by coupling model. Secondly, isothermal crystallization experiments were performed at 363 K (Tg+ 16.5 K), 373 K (Tg+ 26.5 K), and 383 K (Tg+ 36.5 K). The kinetics of crystallization, obtained from the normalized dielectric strength, was modeled using the Avrami model. Havriliak-Negami (HN) shape parameters, αHNand αHN.βHN, were analyzed during the course of crystallization to understand the dynamics of amorphous phase during the emergence of crystallites. HN shape parameters indicated that long range (α-like) were motions affected to a greater extent than short range (β-like) motions during isothermal crystallization studies at all temperature conditions. The variable behavior of α-like motions at different isothermal crystallization temperatures was attributed to evolving crystallites with time and increase in electrical conductivity with temperature. © 2013 Wiley Periodicals, Inc. and the American Pharmacists Association J Pharm Sci 103:167-178, 2014