This item is only available for download by members of the University of Illinois community. Students, faculty, and staff at the U of I may log in with your NetID and password to view the item. If you are trying to access an Illinois-restricted dissertation or thesis, you can request a copy through your library's Inter-Library Loan office or purchase a copy directly from ProQuest.
Permalink
https://hdl.handle.net/2142/20605
Description
Title
Flow properties of a colloidal gel
Author(s)
Rueb, Christopher John
Issue Date
1994
Doctoral Committee Chair(s)
Zukoski, Charles F.
Department of Study
Chemical and Biomolecular Engineering
Discipline
Chemical Engineering
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Chemistry, Physical
Engineering, Chemical
Language
eng
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.
Use this login method if you
don't
have an
@illinois.edu
email address.
(Oops, I do have one)
IDEALS migrated to a new platform on June 23, 2022. If you created
your account prior to this date, you will have to reset your password
using the forgot-password link below.
