Connecting Structure and Dynamics to Rheological Performance of Complex Fluids.

This dissertation reports the development of novel experimental techniques to measure and characterize the microstructure of complex fluids and then link this microstructure to macroscale properties such as rheology and fluid dynamics. This connection between microstructure, dynamics and rheology was studied for the cases of dilute solutions of poly(ethylene) oxide (PEO), single-walled carbon nanotubes (SWCNTs), and rigid rod colloids of polyamide. Aqueous solutions of PEO were found to be in a state of molecular aggregation. We showed that different aggregation states can be generated in dilute solutions of PEO by addition of chaotropic salts. DLS relaxation spectra of high molar mass PEO solutions in the no salt limit showed a power law scaling with exponent three, consistent with internal fluctuations of a large polymer aggregate coil. Addition of salt shifted the DLS relaxation rate scaling to two, consistent with polymer centre of mass diffusion. Such modulation of aggregate structure in PEO shifted the onset of drag reduction by a factor of 2.5 and thus was found directly related to its drag reducing behavior. We introduced a fast, non-invasive and reproducible method based on multi-angle depolarized dynamic light scattering to characterize the length and diameter of SWCNTs. Carbon nanotube dimensions were determined from simultaneous characterization of the mean translational and rotational diffusivities and by using a anisotropic rigid rod model. The method was found to have quality comparable to the standard methods such as atomic force microscopy and transmission electron microscopy; however, the scattering method developed required much less time to execute. Arrested dynamics was studied in a simple model system consisting of self-assembled polyamide anisotropic colloids via methods like confocal laser scanning microscopy and rheology. The glass transition volume fraction obtained in this study was found to be aspect ratio dependent, but was slightly lower than the theoretical and simulation scaling predictions for the minimum percolation volume fraction in a random homogenous network of rods. Rheological characterization revealed a unique power law scaling with exponent three for the elastic modulus, irrespective of the aspect ratio of the rod suspension studied.PhDChemical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/77821/1/amshetty_1.pd