MOLECULAR MOTIONS IN SOLID CHLOROPENTAMETHYLBENZENE - A THERMALLY STIMULATED DEPOLARIZATION CURRENTS STUDY

The dipolar relaxation mechanisms present in solid chloropentamethylbe nzene have been studied using the technique of thermally stimulated di scharge currents (TSDC). A relaxation peak observed at ca. -150 degree s C has been attributed to the onset of the reorientational freedom in the crystal and is believed to correspond to the transition between a n ordered phase and a rotationally disordered phase. At higher tempera tures, ca. 10 degrees C, another relaxation peak appears in the TSDC s pectrum of chloropentamethylbenzene, whose assignment at the molecular level is not yet completely elucidated. Taking into account other res ults from the literature, it is suggested that this peak could arise f rom self-diffusional motions in the solid, which probably involve out- of-plane molecular tumbling as well as in-plane molecular motions. The results obtained in the present work are compared with those obtained , by the same technique, on other hexasubstituted benzenes. In this co ntext, some general features of the TSDC technique are discussed, name ly the existence of a general relationship between the activation para meters associated with the different individual components of the rela xations in the TSDC spectrum, independent of the materials under study and of the nature of the observed relaxations; A reformulation of the so-called 'zero entropy condition' is also presented.