Particle dynamics in the microchannel flow of Carbopol-based yield-stress fluids

Yield-stress fluids, widely used in industrial applications such as cement pastes and lithium-ion slurries, primarily consist of dense particulate systems that form networks. Consequently, extensive research has been conducted on their rheological properties and non-Newtonian flow dynamics. Concurrently, lateral particle migration in channel flows has attracted interest because of its impact on the non-homogeneous particle distribution, which affects final product quality. However, lateral migration in a yield-stress fluid with confined geometry remains to be fully elucidated. In this study, the lateral motion and spatial distribution of micrometer-sized beads in microchannels of a carbopol solution were investigated. Owing to their tunable rheological properties and optical transparency, carbopol microgel solutions have been used as model fluids to study particle dynamics. A dual-view imaging system facilitated the identification of two discrete groups in the channel cross section. The first group was located near the channel walls, whereas the second group exhibited a random dispersion pattern in the central region. This contrasts with results reported for macroscale carbopol flows and microscale flows of other non-Newtonian fluids. These discrepancies are attributed to interactions between deformable microgel aggregates and suspended particles, which cannot be accurately predicted using continuum models. This hypothesis was further substantiated using fluorescence experiments that visualized the microscale motion of microgels and suspended particles. These results offer insights into the complex dynamics of particles in microscale flows of macroscopically yield-stress fluids.