ESR evidence of the dynamic crossover in the supercooled liquid states of a series of solid n-alkanes

Abstract

A study of the rotation dynamics of the spin probe TEMPO by electron spin resonance (ESR) spectroscopy in a series of six short- and medium-sized n-alkanes is presented. In addition to the usual crossover effects connected with solid–liquid phase transitions at temperature T_m and the solid–solid transition at T_ss, we find a strong correlation between the change in reorientation at the characteristic ESR temperature T^fast_X1 < T_ss and/or T_m with the ratio T^fast_X1/T_m = 0.76 ± 0.03 and the characteristic dynamic temperature, T_X, obtained from the viscosity data. This indicates the presence of local disordered regions in the crystalline structure which is indeed sensitive to dynamic change at the crossover temperature T_X ≅ T^fast_X1.