8th Liquid Matter Conference September 6-10, 2011 Wien, Austria ...

P8.64Thu 811:10-14:00Quasi-equilibrium and the emergence of solid behaviourin amorphous materialsStephen Williams 1 and Denis Evans 21 Australian National University, Research School of Chemistry, Australian NationalUniversity 0200, Canberra, Australia2 Australian National University, Canberra, AustraliaAmorphous solids are not in a state of equilibrium, rather they are in quasi-equilibrium. A fluidcannot support a stress. If we subject a fluid to a sudden change in strain, a nonequilibrium stressresults that then relaxes to zero. This relaxation cannot be understood in terms of equilibrium statisticalmechanics. In contrast if we subject a solid to the same protocol, initially a nonequilibriumstress results, which then relaxes to some perturbed equilibrium or quasi-equilibrium non-zerostress. Even if the solid like material is able to flow on some much longer time scale, we canstill accurately quantify the observed non-zero stress on a relevant time scale using equilibriumor quasi-equilibrium statistical mechanics. We will assume that this is the fundamental differencebetween a solid and a fluid. Recently we have developed quasi-equilibrium statistical mechanicsfor the case of planar shear. This work shows how solid behaviour emerges in amorphous materialsfrom microscopic considerations. Here the relevant quasi-equilibrium statistical mechanicswill be reviewed. It will be shown how the response in the stress, to a change in the strain, isqualitatively different for a quasi-equilibrium solid relative to a supercooled fluid. New moleculardynamics simulation results will be presented. These show convincingly how this qualitativechange emerges very sharply, upon crossing from a supercooled fluid to a history dependentquasi-equilibrium solid.[1] S. R. Williams and D. J. Evans, J. Chem. Phys. 132, 184105 (2010).[2] S. R. Williams and D. J. Evans, J. Chem. Phys. 131, 024115 (2009).[3] S. R. Williams, and D. J. Evans, Phys. Rev. E, 78, 021119 (2008).[4] S. R. Williams and D. J. Evans, J. Chem. Phys. 127, 184101 (2007).64