Measuring and modeling deformations of topology-defined polymers using in situ scattering in a capillary rheometer

Applications of high molecular weight dilute polymers typically involve extreme shear rates that cause nonlinear deformations and chain scission. Although various microscopy methods have successfully resolved single-molecule deformations for specific biopolymer systems, these techniques are inaccessible to conventional, synthetic polymers undergoing deformation in high shear flows. We present new in situ small-angle neutron scattering measurements using a high-shear capillary rheometer to simultaneously characterize the microstructure and rheology of topologically complex polymers. The resulting scattering is interpreted using a new modeling framework, Gram-Charlier analysis of polymer scattering (G-CAPS), that fingerprints nonlinear deformations of polymers through non-Gaussian moments of the segment density distribution. The method is validated using synthetic data from Brownian dynamics simulations, and applied to capillary rheo-SANS measurements on a series of topology-controlled polymers in high shear rate flows to test the influence of chain topology and extensibility on non-Gaussian polymer deformations. We anticipate that capillary rheo-SANS in combination with G-CAPS will provide powerful new tools to understand and engineer the molecular rheology of polymer fluids.