## LSU Historical Dissertations and Theses

1990

Dissertation

#### Degree Name

Doctor of Philosophy (PhD)

Chemistry

Paul S. Russo

#### Abstract

In chapter One, zero angle depolarized light scattering methods for particle size determinations are demonstrated by a study on aqueous colloidal suspensions of titanium dioxide. Previous results on a poly(tetrafluoroethylene) latex suspension are also briefly recounted and updated to include reanalysis by an additional independent Laplace inversion method, Provencher's CONTIN. Size distributions may be obtained by Laplace inversion of the correlation functions, with excellent agreement among the various Laplace inversion algorithms. Resolution is greatly enhanced, since rotational motions, which are more sensitive to size than translational motions, are detected at zero angle. In Chapter Two, combined static and quasielastic light scattering results are reported on concentrated solutions of poly-$\gamma$-benzyl-$\alpha$,L-glutamate in N,N-dimethylforamide. The recent theories by Shimada, Doe and Okano compare most favorably in a qualitative sense to the experimental data presented herein. The most important points of agreement are: (1) the behavior of the static structure factor is qualitatively described in terms of the number concentration, $\nu$, divided by the critical concentration, $\nu$* (where $\nu$* is a function of the second virial coefficient); (2) the effect of the nematic interaction begins to dominate the static structure factor resulting in an increase in the apparent correlation length; (3) the behavior of the dynamic structure factor is qualitatively described in terms of $\nu$/$\nu$* and orientational terms; (4) the translational diffusion measure by quasielastic light scattering increases with concentration; (5) bimodal decays are observed at the largest concentrations with the slow mode becoming slower and the fast mode becoming faster. After accounting for thermodynamic repulsion, the translational diffusion decreases with increasing concentration to values lower than predicted by Doi and Edwards. When the translational diffusion data in the absence of thermodynamic effects are plotted as a function of $\nu$/$\nu$*, the data all collapse to a single master curve.

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