Granular materials composed of primary colloidal particles are of both scientific and technological importance. The creation of granular systems for fundamental studies of their packing dynamics as well as applications ranging from ceramics processing to low-cost MEMS devices requires the ability to precisely control the granule size, size distribution, shape, and composition. Many methods exist for producing colloidal granules, including fluidized granulation, high shear mixer granulation, and spray drying. However, none of these methods provide adequate control over these important parameters. In this thesis, we use microfluidic-based assembly methods to control granular size, shape, and chemical heterogeneity. We then investigate the packing dynamics of non-spherical granular media using X-ray micro-computed tomography.
Monodisperse spheroidal granules composed of colloid-filled hydrogels are created in a sheath-flow microfluidic device. By exploiting the physics of laminar flow in microchannels, drops composed of silica microspheres suspended in an aqueous acrylamide monomer solution are created within a continuous oil phase. The interfacial tension between these two immiscible fluids drives a Rayleigh-mode instability that promotes drop formation. Next, the drops undergo photopolymerization to create an acrylamide hydrogel that freezes in the desired morphology and composition during assembly. To demonstrate the flexibility of this new granulation technique, we assemble both dense homogenous and Janus granules in both spherical and discoid geometries.
To produce non-spherical granular media, a lithographic-based microfluidic technique known as stop-flow-lithography is employed. Specifically, colloidal granules and microcomponents in the form of microgear, triangular, discoid, cuboid, and rectangular shapes are produced by this approach. In addition, pathways are demonstrated that allow these building blocks to be transformed into both porous and dense oxide and non-oxide structures.
Finally, large quantities of non-spherical colloidal granules of controlled surface roughness are created via stop-flow lithography in cube and rectangular prism geometries of varying polydispersity. Their packing behavior under static and dynamic conditions is investigated by X-ray micro-computed tomography. Their voronoi volume distribution is quantified as a function of granule shape and agitation time using image analysis techniques. These data are then fit to a probabilistic k-Gamma analytical function, which allows one to quantify an order parameter, k, for the jamming condition of low dispersity cube, rectangular prism and bimodal cube granules. We find a steadily decreasing k-value for monodisperse cubes, suggesting local cube rearrangement during consolidation; while monodisperse rectangular granules and a bimodal distribution of cube granules demonstrate a relatively consistent k-value during consolidation, suggesting the local granule configuration remains similar. In each case, the data collapse onto a single master curve, suggesting a qualitatively similar jamming condition during compaction.
|School:||University of Illinois at Urbana-Champaign|
|School Location:||United States -- Illinois|
|Source:||DAI-B 71/12, Dissertation Abstracts International|
|Keywords:||Colloidal granules, Granulation, Microfluidic assembly, Packing|
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