Quantitative link between democratic motions and Adam-Gibbs theory in glassy relaxation.

FRECHERO M. A.

Punta del Este, Uruguay

Conferencia; MEDYFINOL’08- XVI Conference on Nonequilibrium Statistical Mechanics & Nonlinear Physics; 2008

Glasses are not only central for their everyday growing technological relevance. Our efforts to understand their structure and behaviour have faced us with fascinating questions for which we still have only partial answers. Between them, a complete understanding of the molecular underpinnings of the process by which a supercooled liquid achieves amorphous rigidity, is still lacking. In this realm, more than forty years ago Adam and Gibbs proposed a successful theory for glassy relaxation. Its main tenet is the emergence of a heterogeneous scenario consistent in cooperatively relaxing regions (CRR) whose size should grow as temperature is lowered in the supercooled regime since the concerted participation of a progressively increasing number of particles is required in order to perform a relaxation event (as a result of the concurrent loss in configurational entropy). However, the elucidation of the physical nature of such CRRs has not been possible up to date, even when much effort has been devoted towards such appealing picture. A key breakthrough in this direction has been the discovery of dynamical heterogeneities: the fact that mobile particles are not uniformly distributed within these systems but arranged in clusters, while the characteristic times of such dynamical heterogeneities increases as temperature is lowered. A recent finding consistent with this picture is the fact that the structural relaxation (á-relaxation) is performed by means of the occurrence of relatively compact clusters of mobile particles (the "democratic" clusters or d-clusters) which trigger the rapid movement of the system from its local metabasin (groups of closely related similar structures in the potential energy surface where the trajectory of the system is confined for relatively long times) to a neighboring one. Such cooperatively relaxing units, which have been verified in different glass-formers like binary Lennard-Jones systems and supercooled water, and that have recently received experimental support by means of single molecule experiments in a polymeric system, represent natural qualitative candidates for the CRRS of Adam- Gibbs theory. In this work we provide a quantitative test of their temperature dependence which renders precisely the behaviour predicted by such a theory. clusters of mobile particles (the "democratic" clusters or d-clusters) which trigger the rapid movement of the system from its local metabasin (groups of closely related similar structures in the potential energy surface where the trajectory of the system is confined for relatively long times) to a neighboring one. Such cooperatively relaxing units, which have been verified in different glass-formers like binary Lennard-Jones systems and supercooled water, and that have recently received experimental support by means of single molecule experiments in a polymeric system, represent natural qualitative candidates for the CRRS of Adam- Gibbs theory. In this work we provide a quantitative test of their temperature dependence which renders precisely the behaviour predicted by such a theory. á-relaxation) is performed by means of the occurrence of relatively compact clusters of mobile particles (the "democratic" clusters or d-clusters) which trigger the rapid movement of the system from its local metabasin (groups of closely related similar structures in the potential energy surface where the trajectory of the system is confined for relatively long times) to a neighboring one. Such cooperatively relaxing units, which have been verified in different glass-formers like binary Lennard-Jones systems and supercooled water, and that have recently received experimental support by means of single molecule experiments in a polymeric system, represent natural qualitative candidates for the CRRS of Adam- Gibbs theory. In this work we provide a quantitative test of their temperature dependence which renders precisely the behaviour predicted by such a theory.