FOR 1394:  Nonlinear Response to Probe Vitrification

• Subject Area: Physics
• Term: from 2010 to 2018
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 157463299

The nature of the glass transition is one of the frontier questions in statistical and condensed matter physics; slow and complex structural relaxation processes distributed over many decades in time develop in glass forming melts. While considerable progress has been made in recent decades towards understanding viscoelasticity and dynamical arrest in quiescent glass formers, the interplay of glassy dynamics with external fields reveals a wealth of novel phenomena yet to be explored.
Our Research Unit focusses on the effects of strong external fields in glass forming systems in order to understand the complex structural and transport phenomena under far-from equilibrium conditions. Combining experimental, simulational and theoretical efforts we measure and determine the nonlinear response of supercooled metallic, polymeric and silica melts, of colloidal dispersions and of ionic liquids. Applied fields include electric and mechanic fields and forced active probing (“microrheology”), where a single probe is forced through the glass forming host, so that nonlinear stress-strain and force-velocity relations, as well as nonlinear dielectric susceptibilities can be observed.
While the physical manipulation of melts and glasses is interesting in its own right, especially technologically, we 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. Open questions concern the (de-)coupling of different dynamical degrees of freedom in an external field and the ensuing state diagrams: What forces are required to detach a localised probe particle from its initial environment in a supercooled liquid, in a glassy or granular system? Do metallic and colloidal glasses yield homogeneously or by strain localisation under differently applied stresses? Which mechanisms determine field dependent susceptibilities in dielectric and ionically conducting glass formers?

• DFG Programme: Research Units
• International Connection: Austria, United Kingdom

Projects

• Coordinator project (Applicant Fuchs, Matthias )
• Investigation of nonlinear effects in glassy matter using dielectric methods (Applicants Loidl, Alois ;  Lunkenheimer, Peter )
• Nonlinear effects induced by mechanical stresses in glass-forming systems far from equilibrium (Applicant Samwer, Konrad )
• Nonlinear ion transport in glass-forming ionic liquids: Higher harmonic ac currents and electrical creep (Applicant Roling, Bernhard )
• Nonlinear mechanical response of supercooled melts under applied forces (Applicants Fuchs, Matthias ;  Voigtmann, Thomas )
• Nonlinear response from the perspective of energy landscapes (Applicant Heuer, Andreas )
• Nonlinear response in strongly heterogeneous glass-forming mixtures and ion conductors (Applicants Franosch, Thomas ;  Horbach, Jürgen )
• One and two-component colloidal glasses under shear (Applicant Egelhaaf, Stefan U. )
• Rheology and microrheology of homogeneously driven granular matter (Applicants Sperl, Matthias ;  Zippelius, Annette )
• Zentralprojekt (Applicant Fuchs, Matthias )

• Spokesperson: Professor Dr. Matthias Fuchs