Journal of Physical Chemistry B, Vol.124, No.23, 4821-4834, 2020
Influence of the Internal Structure and Intermolecular Interactions on the Correlation between Structural (alpha) and Secondary (beta-JG) Relaxation below the Glass Transition Temperature in Neat Probucol and Its Binary Mixtures with Modified Saccharides
Broadband dielectric spectroscopy (BDS) has been used to study the molecular dynamics and aging process in neat probucol (PRO) as well as its binary mixtures with selected acetylated saccharides. In particular, we applied the Casalini and Roland approach to determine structural relaxation times in the glassy state of the examined systems (so-called isostructural times, tau(iso)). Next, using the calculated tau(iso), primitive relaxation times of the coupling model were obtained and compared to the experimental secondary beta (Johari-Goldstein (JG) type) relaxation times. Interestingly, it turned out that there is a correlation between the beta-JG and the structural (alpha)-relaxation processes below the glass transition temperature (T < T-g) in each investigated sample. This is a new observation compared to previous studies demonstrating that such a relationship exists only in the supercooled liquid state of neat PRO. Moreover, it was revealed that the stretching parameters obtained from the aging procedure are very close to the ones determined by fitting the dielectric data above the T-g with the use of the Kohlrausch-Williams-Watts function, indicating that the aging process is governed by the alpha-relaxation. Complementary Fourier transform infrared and X-ray diffraction measurements allowed us to find a possible reason for these findings. It was demonstrated that although there are very weak intermolecular interactions between PRO and modified saccharides, the intra- and intermolecular structure of PRO is practically unaffected by the presence of modified saccharides.