0000000000315654
AUTHOR
U. Tracht
Dynamical heterogeneities in glass-forming materials
ABSTRACTCooperative dynamics around the glass transition leads to complex motional behavior of the individual molecules, resulting in non-exponential relaxation. The nature of this non-exponentiality is clarified theoretically as well as experimentally. The non-exponentiality may be due to heterogeneous relaxation (superposition of exponential processes with different rate constants) or homogeneous relaxation (identical intrinsically non-exponential processes). A precise definition of both limits is given. It is shown that the type of relaxation, i.e. to which degree heterogeneous and homogeneous contributions are present, reflects geometrical properties of the dynamics. The heterogeneous c…
Nature of the non-exponential primary relaxation in structural glass-formers probed by dynamically selective experiments
Several experimental methods feature the potential to distinguish between slow and fast contributions to the non-exponential, ensemble averaged primary response in glass-forming materials. Some of these techniques are based on the selection of subensembles using multi-dimensional nuclear magnetic resonance, optical bleaching, and non-resonant spectral hole burning. Others, such as the time-dependent solvation spectroscopy, measure microscopic responses induced by local perturbations. Using several of these methods it could be demonstrated for various glass-forming materials that the non-exponential relaxation results from a superposition of dynamically distinguishable entities. The experime…