Influence of Confinement on Dynamical Heterogeneities in Dense Colloidal Samples

TL;DR

This study investigates how confinement between glass plates affects the movement and rearrangements of particles in dense colloidal suspensions, revealing increased glassiness and altered heterogeneity due to layering effects.

Contribution

It provides direct 3D observations of particle dynamics under confinement, linking layering and heterogeneity to confinement-induced glassy behavior in colloids.

Findings

Confinement slows down particle diffusion.

Layering influences the shape of rearranging regions.

Heterogeneous dynamics become more planar with confinement.

Abstract

We study a dense colloidal suspension confined between two quasiparallel glass plates as a model system for a supercooled liquid in confined geometries. We directly observe the three-dimensional Brownian motion of the colloidal particles using laser scanning confocal microscopy. The particles form dense layers along the walls, but crystallization is avoided as we use a mixture of two particle sizes. A normally liquid-like sample, when confined, exhibits slower diffusive motion. Particle rearrangements are spatially heterogeneous, and the shapes of the rearranging regions are strongly influenced by the layering. These rearranging regions become more planar upon confinement. The wall-induced layers and changing character of the spatially heterogeneous dynamics appear strongly connected to the confinement induced glassiness.