Research

We investigate how droplet size and local area fraction affect motion in a highly polydisperse oil-in-water emulsion flowing through a quasi-2D L-shaped chamber. Due to the heterogeneity of the flow, individual droplet speeds are normalized by the local mean speed, averaged over space and time. We observe a pronounced change in the size dependence of normalized speed as droplet diameter becomes comparable to the chamber height. The small 3D droplets travel at the speed of the fluid, whereas the larger 2D droplets slow with increasing size due to viscous drag against the confining walls. This size dependence is stronger at lower local area fractions. Increasing local area fraction reduces these differences, suggesting that crowding couples the motion of droplets of different sizes. These results highlight how confinement and local packing together regulate droplet motion in polydisperse emulsions.

We investigate the flow of highly polydisperse emulsion droplets confined to a quasi-2D geometry. We produce stable oil-in-water droplets with an average radius of ~40 μm, spanning a size range from ~20 μm to ~200 μm, and a polydispersity index of 0.4. The droplets are driven through a custom-designed L-shaped chamber with height 100 μm. Droplets are forced to rearrange as they navigate around the corner of the L-shaped flow chamber. The nonaffine motion is the difference between the time-and-droplet-averaged flow field and the instantaneous displacements of individual droplets. We observe the largest droplets having distinctly different flow behaviors than the smallest droplets: the smallest droplets frequently have to move around the larger ones, giving the smallest droplets more nonaffine motion. We also study how the nonaffine motion depends on the area fraction of the droplets, ranging from dilute to jammed conditions.