Relaxation and Diffusion in Complex Systems

Experimental evidences of universal relaxation and diffusion properties in complex materials and systems are presented. The materials discussed include liquids, colloids, polymers, rubbers, plastic crystals, biomolecules, ceramics, electrolytes, fuel cell materials, molten salts, inorganic, organic, polymeric and metallic glass-formers. The origin of the universal properties is traced to the relaxation dynamic of interacting many-body systems, rigorous theory of which does not exist as this time. However taking advantage of some insight and guides by solutions of much simplified models, predictions of the properties have been generated. The predictions can explain qualitative as well as quantitative in many cases the experimentally observed properties of different complex materials, essentially from the strength of the many-body interaction. The success provides some measure of understanding the relaxation properties of complex interacting systems and also paves the way for the construction of rigorous theories in the future. Change of relaxation dynamics when dimensions are reduced to nanometer scale are also considered and discussed.