9223212 Schrag This research is in the general area of conformational dynamics in polymer molecules in solution. Experimental studies of the oscillatory flow birefringence (OFB) and viscoelasticity (VE) of polymer solutions subjected to small-amplitude, periodically time- varying shear flows will be carried out under conditions that will explore the entire motional regime of importance in these experiments. Some investigations will utilize custom instrumentation for wide effective frequency range measurements in highly viscous solvents which also provide important temperature dependence information; other instruments providing moderate to high frequency data will be employed to obtain wide frequency coverage in low viscosity solvents. Detailed experimental studies of the effects of solute-induced solvent dynamics modifications, solute concentration, temperature, molecular weight, overall chain geometry (branching), solvent quality and different polymer and solvent species on OFB and VE properties will be initiated or continued, and compared with various theoretical predictions. Generalized bead-spring model calculations of the frequency dependence of the polymer contribution to VE and OFB properties (dilute solutions) will be carried out for irregular combs (randomly placed branch sites), randomly branched chains and chains with spatially varying hydrodynamic interaction to assess the potential of chain dynamics in general, and these techniques in particular, for detailed branching characterization of polymers. Experimental studies and theoretical predictions of OFB and VE properties of dilute block copolymer solutions will also be undertaken to quantitatively assess the characterization potential of this combination of dynamics experiments for block copolymers. This research is a combined experimental and modeling study of the behavior of polymers in solution, especially with respect to the influence of the solvent of the motions of the macromolecules. ***
