| This dissertation investigates the transport of ions and particles and dynamics in polymer systems. The first study is of structural changes in agarose gels as ions migrate through them under applied electric fields (E-fields). The second is on the translational diffusion of probes in polymer solutions and gels, using poly(vinyl alcohol) (PVA) as a model system. Understanding the transport of particles and ionic migration is important for applications such as biomedical devices and gel electrophoresis.; In the first study, I performed small-angle light scattering (SALS) on agarose gels in E-fields, and observed anisotropic SALS patterns, which developed more quickly at higher E-fields and were more anisotropic at higher polymer concentration. Analysis of the data using a model of oriented rods suggested that these patterns arose from rod-like domains 10-15 microns in length oriented perpendicular to the applied field. Microscope imaging revealed rod-like domains on the same length scale, also aligned perpendicular to the E-field. Profiles of pH variation across the gel, measured by video photography, indicated that the anisotropic patterns appeared when the H+ and OH - ions, migrating in opposite directions, met. Calculations of pH profiles using a model based on electro-diffusion reproduced several features of the measured pH profiles. This study showed that electrolysis and the resulting ion migration produce pH changes that are correlated with macroscopic shrinking and orientation of the gel.; In the second study, I used fluorescence correlation spectroscopy (FCS) to study probe diffusion in PVA solutions and cross-linked gels to obtain diffusion coefficients, D, of nanosized particles as a function of PVA concentration, c, and cross-link density. For probes smaller than the correlation length, x, of the polymer solution, diffusion followed D/D0 = e-acn , as suggested by various models, with n depending on solvent quality Diffusion of small particles (R < x) in PVA gels of various concentrations and cross-link densities was found to decrease with increasing cross-link density. Remarkably, the diffusion times of the nanoscale probes in the gels exhibited a linear correlation with the macroscopic elastic modulus of the gels. These studies show that FCS measurements are sensitive to a wide range of length scales. |
