Structural Evolution of Colloidal Gels During Constricted Microchannel Flow

Abstract

We investigate the structure of colloidal gels flowing through constrictions in microchannels using confocal microscopy. As the gel traverses the constricted region, both the average velocity and particle density increase downstream. While the average flow profile is smoothly varying, stagnation zones develop at the constriction entry, leading to markedly nonuniform local flow profiles. Dense clusters undergo shear-induced yielding at intercluster boundaries, which enhances the structural heterogeneity of the suspension at the constriction outlet.

Aqueous Colloid + Polymer Depletion System for Confocal Microscopy and Rheology

“…Upon adding polymer, the viscosity of the suspension became shear-thinning, as previously observed for PMMA/PS depletion gels [69,70]. The corrected N 1 was nearly zero over the same range of shear rates (0.1-10 s −1 ) as for the suspension with no added polymer, then decreased only to −90 ± 30 Pa as the shear rate was further increased.…”

Colloidal oxide nanoparticle inks for micrometer-resolution additive manufacturing of three-dimensional gas sensors

“…However, further increase of molecular weight (M n = B60 000 g mol À1 ) causes chain entanglement, which plays a dominant role in increasing viscosities. 40 Additionally, the optimum amount of PEI should be determined, since an insufficient amount of PEI can cause particle agglomeration and inhomogeneity of the suspension, while excess addition can promote the cracking of printed structures during drying and degreasing. 38 In this regard, we investigate the change in average particle size and zeta potential of the 0.05 wt% SnO 2 suspension with 0-12 wt% of PEI (by weight of SnO 2 ) under different pH conditions (Fig.…”

“…An insufficient amount of PEI addition can cause the bridging interactions between nanoparticles, resulting in a flocculation-induced size increase. 38,40 However, as the amount of PEI was increased, the particle size eventually decreased to B145 nm and remained unchanged. The results indicate that the optimal dispersing effect of PEI appears at weight ratios of 10-12 wt% to the SnO 2 nanoparticles to minimize agglomeration.…”

“…The rapid increase of suspension viscosity at higher-solid loading indicates the formation of gel networks and a pronounced elasticity response. 40 The dependence of viscosity on the volume fraction of SnO 2 nanoparticles at a shear rate of 1 s À1 was fitted by the Krieger-Dougherty model as follows: 42…”

Measuring Advection and Diffusion of Colloids in Shear Flow

“…The recent emergence of microfluidics has further enhanced this interest by adding shear flow as an additional dimension to the problem. The combination of confinement and spatially varying flow has been addressed at the level of the advective velocity and concentration profiles [5,6,[13][14][15][16][17]. However data on the diffusive dynamics in flow are scarce, especially for Brownian particles.…”