The effect of shear on colloidal aggregation and gelation studied using small-angle light scattering

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Show simple item record Mokhtari, Tahereh 2007-04-27T15:27:56Z 2007-04-27T15:27:56Z 2007-04-27T15:27:56Z
dc.description.abstract We investigated the effect of shear on the structure and aggregation kinetics of unstable colloids using small angle light scattering. We used an aqueous suspension of 20 nm polystyrene latex microspheres and MgCl2 to induce aggregation. The sample was only sheared once for approximately 33 seconds at different times, typically 1 min., 5 min., or 15 min., after the onset of aggregation. The average shear rate was in the range of 0.13 - 3.56 s-1, which was in a laminar regime. The unsheared sample gelled after ca. 45 min. When the sample was sheared soon after the onset of aggregation, the aggregation followed DLCA kinetics to yield = 1.80 ± 0.04 aggregates unaffected by the shear. The gel time also remained the same as the unsheared gel. Shearing at later stages of aggregation shortened the gel time and enhanced the scattered light intensity significantly indicating rapid growth. Then, depending on the shear rate, there were three different behaviors. At high shear rates, the aggregate structure was inhomogeneous after the shear was stopped with a crossover in slope in the scattered light intensity vs. q, to imply hybrid superaggregates with two different fractal dimensions. At intermediate shear rates far from the gel point, there was a similar crossover after the shear was stopped; however, the fractal dimension regained 1.80 ± 0.04 at the gel point. At low shear rates, the aggregation rate was increased, but the aggregate structure was uniform, and the fractal dimension remained 1.75 ± 0.05. en
dc.description.sponsorship National Science Foundation grant CTS0403864 en
dc.language.iso en_US en
dc.publisher Kansas State University en
dc.subject Light Scattering en
dc.subject Aggregation en
dc.subject Gelation en
dc.subject Shear en
dc.title The effect of shear on colloidal aggregation and gelation studied using small-angle light scattering en
dc.type Report en Master of Science en
dc.description.level Masters en
dc.description.department Department of Physics en
dc.description.advisor Christopher M. Sorensen en
dc.subject.umi Physics, Condensed Matter (0611) en 2007 en May en

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