Date of Award
Doctor of Philosophy (PhD)
Paul S. Russo
The solution behavior of hydroxypropylcellulose (HPC) was investigated in detail via molecular probe diffusion. The diffusivities of two very different probes, polystyrene latex spheres and sodium fluorescein dye, in aqueous solutions of HPC of three different molecular weights were measured by quasielastic light scattering (QELS) for latex probes and fluorescence photobleaching recovery (FPR) for dye probes. In aqueous HPC, the latex spheres have a tendency to form clusters by adsorption of HPC and bridging of the latex spheres. The microviscosities calculated from the Stokes-Einstein relationship using the bare spheres radii exceeded the measured shear viscosities from cone and plate and suspended capillary viscometers. When the clusters sizes here used to recalculate the microviscosity, agreement was found between the microviscosity and the measured viscosity. Addition of a surfactant can prevent surface interactions between the probe and HPC. The nonexponentiality of the autocorrelation function from QELS measurements of ternary solutions can lead to erroneous results when only simple cumulants analyses are used. Rigorous analyses of the autocorrelation functions utilizing two Laplace inversion routines revealed a bimodal distribution. The stronger slower mode was associated with the diffusion of the latex. The Stokes-Einstein equation failed two-fold at high concentration, even after resolving the two modes, but not at as dramatically as observed by others. Diffusivity of sodium fluorescein dye was measured by FPR in 0-70% HPC solutions, spanning both the isotropic and lyotropic liquid crystal regime. Probe diffusivities decrease almost exponentially with HPC concentration. Measurements made as a function of temperature showed that the dye followed Arrhenius behavior. The experimental data were compared to the "universal curve", the Fujita free volume theory, and obstruction theories by Fricke, and Mackie and Meares. In general, all of these theories seem to be less successful for dye diffusion in HPC than they are for dye or solvent diffusion in linear random coil polymers. It is not clear why this should be so. However, specific interaction between the dye and HPC was ruled out by a series of fluorescence spectroscopic measurements.
Mustafa, Mazidah Binti, "Molecular Dynamics of Solutions Containing Water-Soluble Semiflexible Polymer." (1990). LSU Historical Dissertations and Theses. 5004.