Imaging the spatiotemporal heterogeneities of gelling nanoemulsions

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. These data suggest 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.