Dielectric Spectroscopy in Ibuprofen-Dioxane Mixture

Abstract

In recent years, the dielectric study of amorphous pharmaceuticals has made a considerable effort towards correlating the molecular mobility with their physical and chemical stability. The molecular mobility of amorphous materials is affected by temperature, additives (such as water) and specific interactions (such as Hydrogen bond). Therefore, to understand the physicochemical instability of amorphous materials, nature of their molecular mobility needs to comprehend. In this order, the Dielectric and Calorimetric measurements were performed on a mixture of ibuprofen and 1,4-dioxane. The dielectric spectroscopy reveals two relaxation processes, (designated as αD, and α) in the supercooled region. The spectral shape of αD and α process can be explained satisfactorily throughout the frequency range using Havriliak-Negami (HN) shape function. The αD process is found to be Debye-like (i.e., αHN=0 and βHN=1) in nature and α process kinetically freezes at Tg-onset (DSC) implies that α- process indeed corresponds to the glass transition event. Both processes are found to be non-Arrhenius in nature. In addition, two secondary relaxation processes (designated as βJG and β) are observed and are comparable with the literature. The activation energy of β process indicates that it‟s originating from the fluctuations of the side group larger than -OH group. Also, the calculated fragility index demonstrates that ibuprofen is a fragile glass former.