Space and time dynamical heterogeneity in glassy relaxation. The role of democratic clusters

• Autores: Appignanesi, Gustavo Adrian; Rodriguez Fris, Jorge Ariel
• Año de publicación: 2009
• Idioma: inglés
• Tipo de recurso: artículo
• Materia: GLASSES; DYNAMICSL HETEROGENEITIES; RELAXATION; GLASS TRANSITION
• Institución: Consejo Nacional de Investigaciones Científicas y Técnicas

In this work we review recent computational advances in the understanding of the relaxation
dynamics of supercooled glass-forming liquids. In such a supercooled regime these systems
experience a striking dynamical slowing down which can be rationalized in terms of the picture
of dynamical heterogeneities, wherein the dynamics can vary by orders of magnitude from one
region of the sample to another and where the sizes and timescales of such slowly relaxing
regions are expected to increase considerably as the temperature is decreased. We shall focus on
the relaxation events at a microscopic level and describe the finding of the collective motions of
particles responsible for the dynamical heterogeneities. In so doing, we shall demonstrate that
the dynamics in different regions of the system is not only heterogeneous in space but also in
time. In particular, we shall be interested in the events relevant to the long-time structural
relaxation or α relaxation. In this regard, we shall focus on the discovery of cooperatively
relaxing units involving the collective motion of relatively compact clusters of particles, called
?democratic clusters? or d-clusters. These events have been shown to trigger transitions between
metabasins of the potential energy landscape (collections of similar configurations or structures)
and to consist of the main steps in the α relaxation. Such events emerge in systems quite
different in nature such as simple model glass formers and supercooled amorphous water.
Additionally, another relevant issue in this context consists in the determination of a link
between structure and dynamics. In this context, we describe the relationship between the
d-cluster events and the constraints that the local structure poses on the relaxation dynamics,
thus revealing their role in reformulating structural constraints.
Fil: Appignanesi, Gustavo Adrian. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto de Química del Sur. Universidad Nacional del Sur. Departamento de Química. Instituto de Química del Sur; Argentina
Fil: Rodriguez Fris, Jorge Ariel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto de Química del Sur. Universidad Nacional del Sur. Departamento de Química. Instituto de Química del Sur; Argentina