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 Title: Flow properties of a colloidal gel Author(s): Rueb, Christopher John Doctoral Committee Chair(s): Zukoski, Charles F. Department / Program: Chemical and Biomolecular Engineering Discipline: Chemical Engineering Degree Granting Institution: University of Illinois at Urbana-Champaign Degree: Ph.D. Genre: Dissertation Subject(s): Chemistry, Physical Engineering, Chemical Abstract: 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. Issue Date: 1994 Type: Text Language: English URI: http://hdl.handle.net/2142/20605 Rights Information: Copyright 1994 Rueb, Christopher John Date Available in IDEALS: 2011-05-07 Identifier in Online Catalog: AAI9503305 OCLC Identifier: (UMI)AAI9503305
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