(550a) Spatiotemporal Heterogeneities of Gelling Nanoemulsions in Nozzle Flows

The interplay between pressure-driven flow and attractive interactions in emulsion gels results in complex 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. Image processing of the heterogeneous flows demonstrate 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. The results suggest that nanoemulsions form clusters that give rise to confined flows and shear-induced migration due to the inherent stress and velocity gradients within a cylindrical nozzle geometry, and explains the heterogeneities observed in 3D printing of the nanoemulsions.