|Name||Ms. Divya Bahadur|
Rheology of Thermo-reversible Colloidal Gels
Divya Bahadur, John C. Telotte, Subramanian Ramakrishnan
Department of Chemical and Biomedical Engineering, FAMU FSU College of Engineering, Tallahassee, FL
The scaling of mechanical properties of colloidal gels was investigated as a function of attraction strength and concentration for a system of octadecyl silica particles in decalin at moderate particle loadings (0.2 – 0.4). These particles behave like hard spheres at room temperature, however, gels can be formed reversibly upon quenching the temperature. Rheological experiments were carried out to determine the gel transition temperatures (Tgel), elastic moduli (G’), growth rate of the moduli (Γg) as well as yield stresses (τy) for particle sizes varying by an order of magnitude (18 – 185 nm). We observed good collapse of the experimental data on to master curves using scaling relations derived from the Activated Barrier Hopping framework emphasizing the importance of local structure (localization length) over long-range correlations in determining the mechanical properties of such gels. Poor collapse was seen however when data for different particles sizes were scaled using relations suggested by percolation models indicating the breakdown of fractal concepts at moderate particle loadings. In addition, we find excellent agreement between the experimentally determined and theoretically predicted gel boundaries, elastic moduli and yield stresses using the barrier hopping framework.