Cooperative and local relaxations in complex systems : polymers and crystals

Abstract

A method for investigating the nature of thermally activated relaxations in terms of their cooperative character is tested both in low molecular weight crystals and polymers. This approach is based on the analysis of the activation entropy. In the betaine arsenate/phosphate (BABP) mixed systems we will study the effect of pressure and concentration, whereas in the rubidium ammonium dihydrogen arsenate (RADA) mixed crystal system the effect of concentration and deuteration in the relaxation processes will be studied. Several relaxations have been also studied in polymeric systems, trying to cover representative processes such as the slow g-relaxation in polymers, the i-relaxation in liquid crystalline polymers and the crystalline f-relaxation of semicrystalline polymer (fc).