Microrheology of inhomogeneous complex fluids.

This work is focused on the microrheological studies of inhomogeneous complex fluids using diffusing wave spectroscopy (DWS) and fluorescence microscopy. In the study of the microrheology of associating polymer (AP) solutions using DWS, a change in the relaxation time of the autocorrelation function was observed between 0.25% and 0.5% AP solutions, which can be attributed to the onset of a physically crosslinked structure in the solution. For several AP concentrations, probe particles of different sizes were used and the mean square displacements (2(t)>) were investigated. For an AP concentration of 4.0 wt.%, substantial discrepancies were observed among the 2(t)> of different particle sizes, which was not predicted in the generalized Stokes-Einstein theory. After additional experiments of probe beads of different surface chemistry and a known homogeneous system (high M.W. PEO aqueous solutions), we hypothesized that the inhomogeneous structures in the AP solutions are the likely cause of the observed probe size effect. A modified CONTIN algorithm was used to convert 2 (t)> to storage and loss moduli, G'(o) and G″(o). The results were compared with linear viscoelasticity measurements made by mechanical rheology. A qualitative agreement was achieved. In the study of the microrheology of complex fluids using fluorescence microscopy, an image processing algorithm was first developed and evaluated for images captured from both epifluorescence microscopy (EFM) and confocal laser scanning microscopy (CLSM). The code was able to successfully process the images and simultaneously locate multiple particle centers. A particle trajectory linking code was developed to link positions of each particle in different images and form particle trajectories. In addition, several practical methods were proposed to achieve subpixel resolution in image processing. The results of those methods were further discussed in terms of subpixel adjustment distributions. The correlative motions of particle pairs (distinct 2(t)>) were computed and compared with single-particle corrective motions (self 2(t)>). For inhomogeneous materials such as 5.0 mM/5.0 mM CTAB/NaSS solutions and PMMA/DOP concentrated colloidal suspensions (&phis; = 0.38), significant discrepancies between self and distinct 2(t)> were observed. In addition, deviation of the particle displacement distribution from the Gaussian distribution was found in these materials.PhDApplied SciencesChemical engineeringPhysical chemistryPure SciencesUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/123898/2/3106114.pd