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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
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
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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