Broadband dielectric spectroscopic studies of acemetacin, colchicine and bezafibrate during quench cooling, and in supercooled liquid phase by dielectric modulus formalism

Abstract

This study investigates the dielectric properties of three pharmaceutical melt samples during quench cooling, focusing on the molecular relaxations above and below the glass transition temperature (Tg). Broadband dielectric spectroscopy was employed to analyze the temperature dependence of dielectric permittivity and dielectric loss as the melts were cooled to a deep glassy state at different test frequencies at cooling rate of 10 K/min. Comparative study of complex dielectric permittivity and dielectric modulus in supercooled liquid and glassy states while quench cooling helps to understand the nature of glass transition phenomenon in the pharmaceuticals which are useful for preparing amorphous pharmaceuticals. The primary structural relaxation process above the glass transition temperature and the secondary relaxation process below Tg were examined to provide a comprehensive understanding of the evolving glass transition theory. Additionally, the frequency dependence (10–2–107 Hz) of the real and imaginary parts of complex dielectric modulus were analyzed on heating the glassy samples formed by quench cooling up to just below melting temperature, and the data were fitted using the Havriliak–Negami and Vogel–Fulcher–Tammann equations to extract relevant parameters. The findings offer valuable insights into the glass transition behavior and stability of complex amorphous pharmaceuticals.