# Structural rearrangements that govern flow in colloidal glasses

Peter Schall, David A. Weitz, Frans Spaepen Science 318, 1895 (2007)

## Soft Matter Keywords

Colloid, Glass

## Abstract

## Soft Matter Example

## Experiment

The authors created a glass out of silica spheres <math>1.5 \mu m</math> radius spheres. The spheres were collected on a coverslip by centrifrugation at a packing faction of 0.61, which is higher than needed to created a glass and at a height of <math>42 \mu m</math>. A water-dimethylsulfoxide-fluorescein mixture was used to index match the spheres and then to contrast the spheres against the solvent. Then with the top stabilized, the coverslip at the bottom is sheared at rates about <math>10^{-5}s^{-1}</math>. The authors then recorded 3 Dimensional stacks using confocal microscopy.

The stacks revealed how the colloidal glass rearranged over the course of 20 minutes. The authors find that the strain is oscillatory, which they attribute to brownian motion. To confirm this, the authors analyze the glass in small cubic sections and measure the elastic energies. From this, they find that the distribution is exponential as indicated by the linearity of the semi-log graph in Figure 2.

The use what appears to be a Maxwell-Boltzmann distribution to associate the frequency to the energy, temperature and shear modulus (<math>\mu</math>,) <math>ln(f(E)=\mu \frac{E}{\mu k_B T}</math>. Using this, the shear modulus is calculated to be one half of a value previously measured in a colloidal glass. The authors interpret this as confirmation that the oscillations in strain are thermally induced.

The thermally oscillations are necessarily reversible.