Simple versus cooperative relaxations in complex correlated systems

A method for investigating the nature of thermally activated relaxations in terms of their cooperative character is tested in both polymer and low mol ecular weight crystal systems. This approach is based on analysis of the ac tivation entropy in order to describe thermally activated relaxations. The betaine arsenate/phosphate mixed system of low molecular weight crystals wa s selected for investigation because pure compounds of this system show fer ro-/antiferroelectric phase transitions and the mixed crystals undergo diff erent kinds of relaxation processes involving both dipole-dipole and dipole -lattice interactions. The polymer chosen was a side chain liquid-crystalli ne polysiloxane, which shows the beta -relaxation characteristic of disorde red systems and amorphous materials. The cooperative versus local character of the relaxations is described in terms of "complex'' and ''simple'' rela xations based on calculations of the activation entropies. The initial assu mptions of the theory, as well as the resulting equations, were found to be applicable to the systems studied. (C) 2001 American Institute of Physics.