title: Structural origin of enhanced slow dynamics near a wall in glass-forming systems.
abstract: Spatial confinement is known to induce a drastic change in the viscosity, relaxation times, and flow profile of liquids near the glass (or jamming) transition point. The essential underlying question is how a wall affects the dynamics of densely packed systems. Here we study this fundamental problem, using experiments on a driven granular hard-sphere liquid and numerical simulations of polydisperse and bidisperse colloidal liquids. The nearly hard-core nature of the particle-wall interaction provides an ideal opportunity to study purely geometrical confinement effects. We reveal that the slower dynamics near a wall is induced by wall-induced enhancement of 'glassy structural order', which is a manifestation of strong interparticle correlations. By generalizing the structure-dynamics relation for bulk systems, we find a quantitative relation between the structural relaxation time at a certain distance from a wall and the correlation length of glassy structural order there. Our finding suggests that glassy structural ordering may be the origin of the slow glassy dynamics of a supercooled liquid.
authors.affiliation: Institute of Industrial Science, University of Tokyo, 4-6-1 Komaba, Tokyo 153-8505, Japan.
authors.forename: Keiji
authors.initials: K
authors.lastname: Watanabe
authors.forename: Takeshi
authors.initials: T
authors.lastname: Kawasaki
authors.forename: Hajime
authors.initials: H
authors.lastname: Tanaka