Nose Temperature and Anticorrelation between Recrystallization Kinetics and Molecular Relaxation Dynamics in...

We probe the dielectric response of the supercooled liquid phase of Morniflumate, a drug with anti-inflammatory and antipyretic properties, studying in particular the pressure and temperature dependence of the relaxation dynamics, glass transition temperature T_g, and recrystallization kinetics. T_g increases by roughly 20 K every 100 MPa at low applied pressure, where the ratio T_g/T_m has a constant value of ∼0.8 (T_m = melting point). Liquid Morniflumate displays two dielectric relaxations: the structural α relaxation associated with the collective reorientational motions, which become arrested at T_g, and a secondary relaxation likely corresponding to an intramolecular dynamics. The relaxation times of both processes scale approximately with the inverse reduced temperature T_g/T. Near room temperature and under an applied pressure of 50 MPa, supercooled Morniflumate recrystallizes in a characteristic time of few hours, with an Avrami exponent of 1.15. Under these conditions, the recrystallization rate is a nonmonotonic function of temperature, displaying a maximum at around 298 K, which can be taken to be the optimum crystal growth temperature T_nose. The β relaxation becomes kinetically frozen at ambient temperature under an applied hydrostatic pressure higher than 320 MPa, suggesting that the Morniflumate glass should be kinetically stable under these conditions.