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ETDs are only available to UIUC Users without author permission U of I Only AAI9503305 (UMI)AAI9503305 http://hdl.handle.net/2142/20605 Zukoski, Charles F. Rueb, Christopher John 2011-05-07T12:44:02Z 2011-05-07T12:44:02Z 10000-01-01 1994 The flow properties of a colloidal suspension are influenced by attractive interactions. In this work we study the mechanical behavior of a weakly flocculated colloidal gel. A model system consisting of silica spheres ($\sigma\approx100$ nm) coated with steryl alcohol chains and suspended in decalin or tetradecane was used. At elevated temperatures these suspensions behave effectively as hard spheres. Lowering the temperature below a well defined gelation temperature, T$\sb{\rm G}$, causes this system to form a space filling gel. The strength of interparticle attractions ($\epsilon$) are controlled by temperature. At T$\sb{\rm G}$ mechanical behavior suggests a percolation transition. The gel microstructure was probed using neutron scattering. The application of high shear causes the gel microstructure to densify. We have characterized the gel relaxation time, G$\sp\prime$, and limit of linearity, $\gamma\sb{\rm M}$, as a function of $\phi$ (constant $\varepsilon$) and as a function of $\varepsilon$ (constant $\phi$). Increasing $\varepsilon$ causes the gel relaxation time to decrease, G$\sp\prime$ to increase and $\gamma\sb{\rm M}$ to decrease. The scaling variable $\phi/\phi\sb{\rm G}$, suggested in percolation theory to describe mechanical behavior near the percolation transition, acts to collapse G$\sp\prime$ and $\gamma\sb{\rm M}$ data suggesting that along lines of constant $\phi/\phi\sb{\rm G}$ these gels are rheologically identical. These gels show a time induced yielding phenomena where upon application of a constant stress the gel first responds as if a solid-like material. The gel creeps slowly with time and after an induction time begins to flow at a steady state rate of deformation. Wall slip was ruled out and instead we suggest that this behavior is related to a relaxation mechanism in the gel. Made available in DSpace on 2011-05-07T12:44:02Z (GMT). No. of bitstreams: 2 license.txt: 4922 bytes, checksum: 910b249b4beec47e7ab768910c8f966f (MD5) 9503305.pdf: 8573803 bytes, checksum: 67afbb6e554912a247c63b3d1dd1f047 (MD5) Previous issue date: 1994 Item marked as restricted to the 'UIUC Users [automated]' Group (id=2) by Howard Ding (hding2@illinois.edu) on 2011-05-07T14:45:01Z Item is restricted indefinitely. Restriction data tranferred 2014-07-01T11:19:53-05:00 Original Data Group with Access UIUC Users [automated] Release Date: none Reason: ETDs are only available to UIUC Users without author permission eng Copyright 1994 Rueb, Christopher John Chemistry, Physical Engineering, Chemical Flow properties of a colloidal gel text Chemical and Biomolecular Engineering Chemical Engineering University of Illinois at Urbana-Champaign Dissertation Ph.D.