The interplay between pressure-driven flow and attractive interactions in colloidal gels results in complex particle trajectories and velocity profiles that are not evident from bulk rheological measurements. We use a colloidal gel system of nanoemulsion droplets of poly(dimethylsiloxane) suspended in a continuous phase, comprised of a liquid precursor that contains poly(ethylene glycol diacrylate). The nanoemulsions undergo self-assembly at elevated temperatures to form gel networks with different length scales. We use high-speed confocal microscopy to investigate its spatiotemporal evolution as it flows through a cylindrical channel at various temperatures and shear rates. The trajectories of fluorescent tracer beads in the oil-rich domains are tracked using 2D image processing. Comparison of the bead velocity profiles to those obtained from a Herschel-Bulkley fit to bulk rheometry data shows agreement at low temperature but not above the gel point. Imaging data collected from cross sections of the channel show that time-dependent variations in cluster properties are responsible for statistically significant deviations from theoretical predictions, especially when attractive interactions are strongest at elevated temperatures.

Spatiotemporal heterogeneities in flowing colloidal gels

ACS Spring 2022

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.