Molecular Rheology

The determination of the viscoelastic response of polymers, while well described by the reptation theory for linear chains, remains an active area of investigation. The works have been particularly strengthened by the ability of the synthetic chemist to make novel molecules having topologies that can differ from the linear chain or that can look like "fat" linear chains diluted by dense side group moieties of differing chain length. These latter are frequently referred to as bottle brush or wedge type polymers. Other architectures are also of interest and the ring molecule or "endless chain" has become of particular interest recently because of developments related to both synthesis and purification of synthetic polymers as well as new developments in extracting large circular DNA molecules from cell cultures. In both instances, while progress is being made, the work has focused on the issues surrounding purity of the ring samples, i.e., freedom from linear chain contamination. In the present investigations we are examining circular DNA in collaboration with researchers C.M. Schroeder at the University of Illinois, Urbana-Champaign and R. M. Robertson-Anderson of the University of San Diego. Both macroscopic and micro-rheology are being used as well as single molecule imaging in elongational flows to characterize the behavior of the ring/linear blends. In the case of the synthetic polymers, we are collaborating with J. E. Puskas at Ohio State University and J.A. Kornfield at the California Institute of Technology. In this case the work is focused on the linear rheological characterization of two new synthetic ring polymers made in the Puskas labs by Reversible Radical Recombination Polymerization (R³P) to make rings having much larger molecular weights than previously achieved by dilute solution ring-closure methods of synthesis. These polymers offer opportunities to improve the rolling resistance response of tires and we are also developing methods to characterize the response of carbon black filled systems as well as to examine elongational viscosity response.

 

Some Publications

1. Z. Qian, D. Chen and G.B. McKenna*, "Re-visiting the"consequences of grafting density on the linear viscoelastic behavior of graft polymers"," Polymer, 186, 121992 (2020).

2. Y. Zhou, K.-W. Hsiao, K. E Regan, D. Kong, G. B. McKenna, R. M. Robertson-Anderson and C. M. Schroeder*, "Effect of molecular architecture on ring polymer dynamics in semidilute linear polymer solutions," Nature Communications, 10, 1753 (2019).

3. Z. Qian, Y. P. Koh, M. R. Pallaka, A. B. Chang, T.-P. Lin, P.E. Guzmán, R. H. Grubbs, S. L. Simon and G. B. McKenna*, "Linear Rheology of a Series of Second-Generation Dendronized Wedge Polymers," Macromolecules, 52, 2063-2074 (2019).

4. Z. Qian and G.B. McKenna*, "Expanding the application of the van Gurp-Palmen plot: New insights into polymer melt rheology," Polymer, 155, 208-217 (2018).

5. Y. F. Li, K.W. Hsiao, C.A. Brockman, D.Y. Yates, R.M. Robertson-Anderson, J.A. Kornfield, M.J. San Francisco, C.M. Schroeder*, and G.B. McKenna*, "When Ends Meet: Circular DNA Stretches Differently in Elongational Flows," Macromolecules, 48, 5997-6001 (2015).

6. M. Hu, Y. Xia, C. Daeffler, J. Wang, G.B. McKenna*, J.A. Kornfield*, and R.H. Grubbs, "The Linear Rheological Responses of Wedge-type Polymers," Journal of Polymer Science, Part B: Polymer Physics, 53, 899-906 (2015).

 

Funding

• National Science Foundation. Division of Chemical, Bioengineering, Environmental, and Transport Systems (CBET).
• U.S. Department of Energy, Office of Science, Basic Energy Sciences.
• John R. Bradford Endowment at Texas Tech University.
• Paul Whitfield Horn Professorship at Texas Tech University.