Light Scattering Study of the Structure Factor of Dilute Polymer Coils in Solution.
Abstract
In this dissertation, we present very accurate laser light scattering experimental results for the conformational and thermodynamic properties of linear flexible polymers in solution of various solvent qualities. All necessary thermodynamic quantities were carefully determined from static light scattering measurements and possible relationships among those quantities were studied. The average conformation (the structure factor S(q)) of polymer coils in solution of various solvent qualities was intensively investigated for a wide range of molecular weights M_ {w} and scattering wavevectors q. For sufficiently low qR_{G}, where R_{G} is the radius of gyration of the polymer coil, the structure factor can be described by the Debye function, which is the structure factor of an ideal random walk Gaussian coil, over the range of solvent qualities investigated. However, for qR_{G} > 1.5, the Debye function does not describe the structure factor perfectly, even in the vicinity of the Theta point, at which polymers behave like a nearly ideal random walk chain. The systematic deviations of the data from the Debye function observed at high qR_ {G} were not experimental artifacts, and cannot be accounted for by the effect of polydispersity. The persistent deviations at high qR_{G } increased as qR_{G} increased. To our knowledge, this is the first experiment to unambiguously establish the non-Debye like structure factor of polymer coils at and near Theta conditions. The results for the structure factors of dilute polymer coils for the polystyrene-cyclohexane system at various temperatures were also compared to the Debye function due to lacking a theoretical form of the temperature-dependent structure factor. We found that except for very small qR_{G}, the structure factor was always larger than theory, and the systematic deviations got larger as qR_{G} and/or temperature increased. For the polystyrene -toluene system (good solvent), we compared S(q) to two recent renormalization group calculations for chains with fully developed excluded volume done separately by Ohta et al. and Duplantier. It was found that Duplantier's calculation described the data better than did that of Ohta et al.
- Publication:
-
Ph.D. Thesis
- Pub Date:
- 1993
- Bibcode:
- 1993PhDT.......212S
- Keywords:
-
- Physics: Molecular; Physics: Condensed Matter