Document Type
Article
Publication Date
1989
Abstract
Static light scattering measurements are reported on narrow molecular weight distribution polystyrenes (Mw = 3.84 × 106) in the four good solvents, ethylbenzene, benzene, toluene, and tetrahydrofuran at 25°C. These data are plotted in a "scaling" form to directly compare the equilibrium structure factor of identical polystyrene samples in the different solvent systems. The results in tetrahydrofuran are clearly distinct from those in the aromatic solvents and apparently suggest that THF is a thermodynamically better solvent. These distinctions between our results for identical, high molecular weight polymer samples in different good solvents demonstrate that these molecular weights are not high enough to be in the asymptotic good solvent limit (at least not in both solvents), so that current experimental values of universal ratios in this limit are not reliable. We also compare dynamic light scattering characteristics of polystyrene samples (Mw = 8.42 × 106 and 20 × 106) in ethylbenzene and in tetrahydrofuran over the small to intermediate qRg region. For qRg < 1.0, we obtain the infinite dilution translational diffusion coefficient 〈Dt〉z0 and at qRg > 1.0, we determine the dimensionless decay rate Γ* = Γe(q,c)/(q3kT/η0), where Γe is the first cumulant of the decay function. The values, Γ*(q), characteristic of a single coil, have been obtained by extrapolating Γe to c = 0. As predicted by theory, the reduced quantity Γ*(q) slowly approaches a constant asymptote at qRg ≫ 1.0. We show that an accurate determination of the asymptote can be obtained from a plot of Γ*(q) versus (qRg)-2. The asymptotic value obtained for polystyrene chains in ethylbenzene is significantly different, about 15% smaller than that determined for polystyrene in tetrahydrofuran. This indicates differences in the internal coil hydrodynamics of polystyrene in these two chemically dissimilar good solvents.
Keywords
benzene, light scattering, solvents, toluene, dynamic scaling relationships, ethylbenzene, static scaling relationship, tetrahydrofuran, polystyrenes
Publication Title
Macromolecules
Rights
© 1989 American Chemical Society. Reprinted (adapted) with permission from Macromolecules 22:3, 1374-1380.
Recommended Citation
Mamta Bhatt, Alex M. Jamieson, and Rolfe G. Petschek. Static and dynamic scaling relationships in the light scattering properties of polystyrenes in good solvents. Macromolecules 1989 22 (3), 1374-1380. DOI: 10.1021/ma00193a061