Fingerprinting Molecular Relaxation in Deformed Polymers

A central problem in polymer rheology is to understand how the intra- and interchain configurations are transformed by the macroscopic deformation. The rheo-small-angle-neutron-scattering (rheo-SANS) technique has long held the promise of offering a molecular perspective on this issue. However, despite decades of development, the full potential of this experimental technique is yet to be realized. By combining and extending several key concepts in the literature and drawing upon the so-called spherical harmonic expansion technique, here we describe a new framework [Phys. Rev. X 7, 031003 (2017); Phys. Rev. Lett. 121, 117801 (2018)] for connecting the SANS experiments and the molecular rheology of polymeric liquids. We show how several two-point spatial correlation functions, such as the anisotropic single-chain structure factor and pair distribution function, can serve as a bridge between rheo-SANS experiments on the one hand and theoretical studies on the other, providing a convenient platform for molecular rheology of polymers. To demonstrate the power of this idea, we will discuss in this talk our recent SANS experiments on deformed homopolymer melts as well as polymer blends.