Search results for "mode coupling theory"
showing 5 items of 5 documents
Residual Stresses in Glasses
2013
The history dependence of the glasses formed from flow-melted steady states by a sudden cessation of the shear rate $\dot\gamma$ is studied in colloidal suspensions, by molecular dynamics simulations, and mode-coupling theory. In an ideal glass, stresses relax only partially, leaving behind a finite persistent residual stress. For intermediate times, relaxation curves scale as a function of $\dot\gamma t$, even though no flow is present. The macroscopic stress evolution is connected to a length scale of residual liquefaction displayed by microscopic mean-squared displacements. The theory describes this history dependence of glasses sharing the same thermodynamic state variables, but differi…
Transport of Mobile Particles in an Immobile Environment: Computer Simulations of Sodium Silicates
2007
Molecular dynamics (MD) simulations of various sodium silicate melts, (Na2O)x(SiO2) with x=2, 3, 20, are presented. In these systems, the mobility of sodium ions is much higher, often by orders of magnitude, than that of the silicon and oxygen atoms forming a tetrahedral network structure. We show that the high mobility of sodium is intimately related to the chemical ordering in sodium silicates. A network of percolating sodium-rich channels is formed in the static structure that serve as diffusion channels for the sodium ions. This channel network is revealed in static structure factors by a prepeak at the wavenumber q=0.95 A-1. Inelastic neutron scattering experiments of sodium silicate m…
Event-Driven Simulation of the Dynamics of Hard Ellipsoids
2008
We introduce a novel algorithm to perform event-driven simulations of hard rigid bodies of arbitrary shape, that relies on the evaluation of the geometric distance. In the case of a monodisperse system of uniaxial hard ellipsoids,we perform molecular dynamics simulations varying the aspect-ratio X0 and the packing fraction phi. We evaluate the translational Dtrans and the rotational Drot diffusion coefficient and the associated isodiffusivity lines in the phi-X0 plane. We observe a decoupling of the translational and rotational dynamics which generates an almost perpendicular crossing of the Dtrans and Drot isodiffusivity lines. While the self intermediate scattering function exhibits stret…
Simulation of the dynamics of hard ellipsoids
2008
We study a system of uniaxial hard ellipsoids by molecular dynamics simulations, changing both the aspect-ratio X-0 (X-0 = a/b, where a is the length of the revolution axis and b is the length of the two other axes) and the packing fraction phi. We calculate the translational and rotational mean squared displacements, the translational D-trans and the rotational D-rot diffusion coefficients and the associated isodiffusivity lines in the phi - X-0 plane. For the first time, we characterize the cage effect through the logarithmic time derivative of log and log . These quantities exhibit a minimum if the system is supercooled and we show that, consistently with our previous findings, for large…
Dynamics of Uniaxial Hard Ellipsoids
2007
We study the dynamics of monodisperse hard ellipsoids via a new event-driven molecular dynamics algorithm as a function of volume fraction $\phi$ and aspect ratio $X_0$. We evaluate the translational $D_{trans}$ and the rotational $D_{rot}$ diffusion coefficient and the associated isodiffusivity lines in the $\phi-X_0$ plane. We observe a decoupling of the translational and rotational dynamics which generates an almost perpendicular crossing of the $D_{trans}$ and $D_{rot}$ isodiffusivity lines. While the self intermediate scattering function exhibits stretched relaxation, i.e. glassy dynamics, only for large $\phi$ and $X_0 \approx 1$, the second order orientational correlator $C_2(t)$ sho…