COMMENTS ON COMPENSATION ANALYSIS AS APPLIED TO THERMALLY STIMULATED CURRENT THERMAL SAMPLING

Compensation of Arrhenius relaxation curves coming to an extrapolated focus point is observed for many materials, especially in thermally st imulated current or related relaxation studies of polymers. Here we co mpare typical thermally stimulated current thermal sampling (t.s.c.-t. s.) data which exhibit compensation phenomena, with simulated data. Th e simulations were constructed on the basis of different curves of app arent activation energies, E-a, vs temperature, in an effort to repres ent a variety of possible experimental systems near a cooperative or h igh activation energy transition such as a glass transition (T-g). We show that compensation is universally observed for all simulated resul ts, essentially independently of the nature of the cooperative transit ion, and proof is given that it is simply a result of mathematical man ipulation of the Arrhenius equation in an under-determined system. The compensation temperature T-c must be related to T-g because of the st eep Arrhenius curves. The difference, T-c - T-g, is indirectly related to the shape of the onset of glass transition as one approaches T-g f rom the low temperature side, but is not related to the 'breadth' of t he main glass transition which is usually the region of interest, nor is it sensitive to the high temperature side of the transition. Correl ating compensation with any physically observable quantity is ill-advi sed, for a variety of reasons discussed here. (C) 1997 Elsevier Scienc e Ltd.