title: Convective Cage Release in Model Colloidal Glasses.
abstract: The mechanism of flow in glassy materials is interrogated using mechanical spectroscopy applied to model nearly hard sphere colloidal glasses during flow. Superimposing a small amplitude oscillatory motion orthogonal onto steady shear flow makes it possible to directly evaluate the effect of a steady state flow on the out-of-cage (α) relaxation as well as the in-cage motions. To this end, the crossover frequency deduced from the viscoelastic spectra is used as a direct measure of the inverse microstructural relaxation time, during flow. The latter is found to scale linearly with the rate of deformation. The microscopic mechanism of flow can then be identified as a convective cage release. Further insights are provided when the viscoelastic spectra at different shear rates are shifted to scale the alpha relaxation and produce a strain rate-orthogonal frequency superposition, the colloidal analogue of time temperature superposition in polymers with the flow strength playing the role of temperature. Whereas the scaling works well for the α relaxation, deviations are observed both at low and high frequencies. Brownian dynamics simulations point to the origins of these deviations; at high frequencies these are due to the deformation of the cages which slows down the short-time diffusion, while at low frequency, deviations are most probably caused by some mild hydroclustering.
authors.affiliation: IESL-FORTH & Materials Science & Technology Department, University of Crete, 71110 Heraklion, Greece.
authors.forename: Alan R
authors.initials: AR
authors.lastname: Jacob
authors.affiliation: Jülich Centre for Neutron Science (JCNS-1) and Institute for Complex Systems (ICS-1), Forschungszentrum Jülich GmbH, 52425 Jülich, Germany.
authors.forename: Andreas S
authors.initials: AS
authors.lastname: Poulos
authors.affiliation: Chemical Engineering Department, Katholieke Universiteit Leuven, Willem de Croylaan 46, 3001 Heverlee, Belgium.
authors.forename: Sunhyung
authors.initials: S
authors.lastname: Kim
authors.affiliation: Department of Materials, ETH Zürich, Vladmir Prelog weg 5, CH-8093 Zürich, Switzerland.
authors.forename: Jan
authors.initials: J
authors.lastname: Vermant
authors.affiliation: IESL-FORTH & Materials Science & Technology Department, University of Crete, 71110 Heraklion, Greece.
authors.forename: George
authors.initials: G
authors.lastname: Petekidis