(326g) Flow and Microstructure of Colloidal Gels with Telechelic Polymers

In this study, we evaluate the rate-driven flow of colloidal gels, with networks formed by telechelic polymer bridges, through a cylindrical channel. Although rheometry measurements, along with non-Newtonian fluid models, are often used to predict the velocity profiles of physical gels, these models fail under many process conditions. To understand why, we experimentally measure the velocity profiles of colloidal gels with varying attractive interaction, and compare them to rheometry-based models. Deviations from these models are correlated to the dynamic gel microstructure. Specifically, we observe a radially dependent microstructure with fluidized gel clusters along the edges of flow and large rigid clusters towards the center of flow. In addition, the relative colloid volume fraction is lower at the edges compared to the center of flow. This structural heterogeneity is due to the force balance between shear forces and attractive interactions, which varies with r-position due to the shear stress gradient that is inherent to cylindrical channel flow. Because the depleted edges behave fluid-like while the large clusters towards the center behave solid-like, the experimental profiles are more plug-like compared to rheometry-based predictions. These trends are most prominent in experiments with the highest colloid-colloid attractive interaction. Our results suggest that when attractive interactions are comparable to shear forces, a transition occurs along the r-axis from dominating shear forces to dominating attractive interactions, which results in two structural phases with distinct flow behaviors.