Understanding the nonlinear dynamics of driven particles in supercooled liquids in terms of an effective temperature

Abstract

In active microrheology the mechanical properties of a material are tested by adding probe particles which are pulled by an external force. In case of supercooled liquids, strong forcing leads to a thinning of the host material which becomes more pronounced as the system approaches the glass transition. In this work we provide a quantitative theoretical description of this thinning behavior based on the properties of the Potential Energy Landscape (PEL) of a model glass-former. A key role plays the trap-like nature of the PEL. We find that the mechanical properties in the strongly driven system behave the same as in a quiescent system at an enhanced temperature, giving rise to a well-characterized effective temperature. Furthermore, this effective temperature turns out to be independent of the chosen observable and individually shows up in the thermodynamic and dynamic properties of the system. Based on this underlying theoretical understanding, we can estimate its dependence on temperature and force by the PEL-properties of the quiescent system. We furthermore critically discuss the relevance of effective temperatures obtained by scaling relations for the description of out-of-equilibrium situations.

Origin of the effective mobility in non-linear active micro-rheology

“…More recently, in Ref. [5] the potential energy landscape approach was used in order to calculate the population distribution of different metabasin energies in the presence of the external force. It was shown that the energy distribution of the system maintains a Gaussian form but becomes shifted towards higher energies, fact that yield the authors to characterize the effect in terms of an effective temperature whose dependence on the force coincides with Eq.…”

“…Comparison between simulation data (symbols) taken from Ref. [5] and the results for the effective mobility given by Eq. (24) (lines) assuming the periodic potential U (x) given in Eq.…”

“…A similar effect has been recently reported in simulations on active non-linear microrheology of supercooled liquids in Refs. [3][4][5] in which the correspondence between simulation results and theory is remarkable, see, for instance, Ref. [3].…”

“…It is convenient to notice that, although the methodology adopted in Ref. [5], where the authors use the potential energy landscape concept, differs notably from that of Refs. [3,4], in which correlation functions of dynamic variables are analyzed, the same effect associated with thermal fluctuations and the effective temperature appears.…”

“…a) Comparison between simulation data (symbols) taken from Ref [5]. and the results for the effective mobility given by Eq.…”