Recent advances on glass-forming systems driven far from equilibrium

Abstract

Abstract. The nature of the glass transition is one of the frontier questions in Statistical Physics and Materials Science. Highly cooperative structural processes develop in glass-forming melts exhibiting relaxational dynamics which is spread out over many decades in time. While considerable progress has been made in recent decades towards understanding dynamical slowing-down in quiescent systems, the interplay of glassy dynamics with external fields reveals a wealth of novel phenomena yet to be explored.This special issue focuses on recent results obtained by the Research Unit FOR 1394 'Nonlinear response to probe vitrification' which was funded by the German Science Foundation (DFG). In the projects of the research unit, strong external fields were used in order to gain insights into the complex structural and transport phenomena at the glass transition under far-fromequilibrium conditions. This aimed inter alia to test theories of the glass transition developed for quiescent systems by pushing them beyond their original regime. Combining experimental, simulational, and theoretical efforts, the eight projects within the FOR 1394 measured and determined aspects of the nonlinear response of supercooled metallic, polymeric, and silica melts, of colloidal dispersions, and of ionic liquids. Applied fields included electric and mechanic fields, and forced active probing ('micro-rheology'), where a single probe is forced through the glass-forming host. Nonlinear stressstrain and force-velocity relations as well as nonlinear dielectric susceptibilities and conductivities were observed. While the physical manipulation of melts and glasses is interesting in its own right, especially technologically, the investigations performed by the FOR 1394 suggest to use the response to strong homogeneous and inhomogeneous fields as technique to explore on the microscopic level the cooperative mechanisms in dense melts of strongly interacting constituents.Questions considered concern the (de-)coupling of different dynamical degrees of freedom in an external field, and the ensuing state a

Velocity Gradient Power Functional for Brownian Dynamics

“…The response of complex systems to external stresses is important, both from an applied point of view of control of flow properties, but also from a fundamental interest in understanding the collective nonequilibrium behaviour of many-body systems [1]. In particular colloidal dispersions, when exposed to shear flow, display a wealth of striking nonequilibrium phenomena, ranging from the nonlinear rheological behaviour of fluids [1] and glasses [2] to shear banding phase transitions [3][4][5]. Much theoretical work has been carried out on the basis of the Smoluchowski many-body equation for overdamped Brownian systems [1].…”