Disengagement: from coil to stretched

1. Exploring universal picture of yielding in entangled polymeric liquids under large deformationShi-Qing Wang, University of Akron, DMR 0804726 The research aims to gain basic knowledge of entangled polymers under large deformations. So far all evidence points to a new theoretical description of nonlinear rheological behavior. The emerging phenomenological picture is only based on the macroscopic observations. It is necessary to obtain some molecular confirmation of the idea about the chain disentanglement upon large deformations. Currently, only DNA molecules are large enough for light microscopy. We have assembled a combination of rheometry and single-molecule imaging velocimetry (SMIV) as shown in the photo and schematic drawing on the right column, which is plausibly the only one in the world. As a first step, we have carried out SMIV observations of molecular behavior at the solution/plate interface during simple shear. For the first time we obtained molecular evidence for wall slip. Moreover, upon after chain disentanglement single DNA tumbling in an entangled solution was observed. See PRL 2010, 105, 027802. In this premier example of shear inhomogeneity, we confirmed the basic conceptual picture that a sudden external deformation on entangled liquids must result in yielding either at the solid boundary or internally in the form of chain disentanglement. tumbling of a freed chain: Stretching – recoil – re-stretch Disengagement: from coil to stretched

2. Exploring universal picture of yielding in entangled polymeric liquids under large deformationShi-Qing Wang, University of Akron, DMR 0804726 • In the area of broader impact, we have several items to report: • Pouyan Boukany and Sham Ravindrananth have graduated with Ph.D and are pursing postdoctoral research and industrial R&D respectively. • Rose Roberts successfully completed her REU summer research. Her work will result in a major publication in the area of solid-liquid transition of a hydrogel under shear. • PI has successfully gone through a book review and signed a contract with Wiley to publish a new textbook on polymer rheology in two years. • PI has given a keynote speech on Aug. 3 at the international Pacific Rim Conference on Rheology. • PI has made a proposal to teach a short course on the latest of polymer rheology in the Society of Rheology, along with two co-instructors, Greg McKenna and Gareth McKinley. The group photo, with the undergrad REU student Rose Roberts. Rose worked effectively in the lab for the summer under the supervision of Xin Li (on the left).