Probing architecture-dependent polymer deformation in extreme shear flows

It is increasingly recognized that molecular architecture plays a significant role in controlling rheology and mechanical stability in applications involving polymers extremely high shear rates. However, in situ measurements of polymer deformation in such high-rate flows have been extremely limited, preventing a broader understanding of the high-rate behavior of architecturally-complex polymers. We report new devices and methods that enable scattering and rheology measurements in situ at shear rates exceeding 10⁶ s^-1. We have employed these methods to understand how polymer architecture influences key rheological properties at extreme shear rates. Specifically, measurements on a well-controlled series of linear, branched and star architectures reveal the primary mechanisms by which architecture controls polymer deformation and scission. Most importantly, we find that star polymers exhibit significantly greater mechanical stability at extreme shear rates relative to linear counterparts, owing primarily to reduced deformations encountered as a result of the faster relaxation dynamics of polymer arms. Overall, our results highlight the importance of characterizing molecular structure in situ to aid the rational design of polymer architectures for high-shear applications.