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High-pressure dielectric studies on global and local dynamics in binary mixtures of nifedipine with acetylated maltose
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DOI：10.1016/j.jnoncrysol.2026.124061.png)
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Abstract
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This paper presents molecular dynamics studies of amorphous binary mixtures composed of nifedipine (NIF) and acetylated maltose (acMAL) with varying molar ratios, using broadband dielectric spectroscopy (BDS) under ambient and high-pressure conditions. Experiments at p = 0.1 MPa revealed that the slower secondary beta-relaxation, manifested as an excess wing in the loss spectra of neat NIF, emerges from the high-frequency flank of the alpha-relaxation peak with the addition of acMAL. High-pressure dielectric measurements and physical aging confirmed the predictions of the Coupling Model, unequivocally identifying the intermolecular Johari-Goldstein (JG) origin of this secondary relaxation in NIF. The faster gamma-process was assigned to intramolecular motions (nonJG mode). Importantly, BDS experiments indicated that acMAL is an effective crystallization inhibitor for NIF under high compression. Moreover, they revealed that the alpha-process in all examined binary systems is characterized by high sensitivity to pressure, and that the isochronal superpositioning of alpha- and beta-relaxation times, as well as the temperature-pressure superpositioning, are satisfied for these mixtures. Finally, analysis of preexponential factors in the Arrhenius formula and activation entropies of both secondary relaxations showed that the beta-JG process exhibits much greater intermolecular cooperativity than the gamma-relaxation, with the former decreasing under compression. Crucially, the glass transition temperature (Tg) revealed a pressure-induced crossover in mixing; nearly ideal mixing occurs at 0.1 MPa, whereas compression changes the Tg -composition dependence from weakly non-ideal (50-150 MPa) to strongly non-ideal (200-250 MPa), reflecting a possible pressure-induced change in the balance between packing/free-volume constraints and effective intermolecular interactions.
Keywords:
Nifedipine
Acetylated maltose
Binary mixtures
High-pressure dielectric studies
Physical stability
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1.9W
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3.3W
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