Experimental evidence of mosaic structure in strongly supercooled molecular liquids
Federico Caporaletti, S. Capaccioli, Sofia Valenti, Mirko Mikolasek, A. I. Chumakov, G. Monaco
Abstract
Abstract When a liquid is cooled to produce a glass its dynamics, dominated by the structural relaxation, become very slow, and at the glass-transition temperature T g its characteristic relaxation time is about 100 s. At slightly elevated temperatures (~1.2 T g ) however, a second process known as the Johari-Goldstein relaxation, β JG , decouples from the structural one and remains much faster than it down to T g . While it is known that the β JG -process is strongly coupled to the structural relaxation, its dedicated role in the glass-transition remains under debate. Here we use an experimental technique that permits us to investigate the spatial and temporal properties of the β JG relaxation, and give evidence that the molecules participating in it are highly mobile and spatially connected in a system-spanning, percolating cluster. This correlation of structural and dynamical properties provides strong experimental support for a picture, drawn from theoretical studies, of an intermittent mosaic structure in the deeply supercooled liquid phase.