Dielectric Relaxation and Crystallization Kinetics of Ibuprofen at Ambient and Elevated Pressure

Dielectric spectroscopy (DS) was used to investigate the relaxation dynamics of supercooled and glassy ibuprofen at various isobaric and isothermal conditions (pressure up to 1750 MPa). The ambient pressure data are in good agreement with that reported previously in the literature. Our high pressure measurements revealed validity of temperature-pressure superpositioning (TPS) for the alpha-peak. We also found that the value of the fragility index decreases with compression from m = 87 +/- 2 at atmospheric pressure to m = 72.5 +/- 3.5 at high pressure (p = 920 MPa). The drop of fragility observed in our experiment was discussed in the framework of the two-order-parameter (TOP) model. In addition, we have also studied crystallization kinetics in a liquid state of examined drug at ambient and high pressure. We found out that, for the same structural relaxation time/same viscosities, the samples prepared by compression of liquid at high temperatures have significantly elongated induction times as well as overall crystallization times (sample 2: t(0) congruent to 4 h, t(1/2) congruent to 37.5 h; sample 3: t(0) congruent to 5.6 h, t(1/2) congruent to 49 h) compared to that held at lower temperature and ambient pressure (sample 1: t(0) congruent to 1.2 h, t(1/2) congruent to 12.2 h). A possible explanation of this finding is also given.