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Los Alamos National LaboratoryCenter for Integrated Nanotechnologies
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2020 Highlights

A selection of CINT science highlights from staff and user research.

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  • Gary Grest
  • Soft, Biological, and Composite Nanomaterials Thrust
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Elongated Ring Polymers Get Tied Up In Knots

Scientific Achievement

Discovered a new flow-driven linking process in ring polymers that explains their anomalous viscosity.

Significance and Impact

Ring knotting is a new mechanism in polymer physics that may be harnessed to design fluids that are selectively viscous to extensional flow but flow easily in other conditions.

Research Details

The image shows a snapshot from a molecular simulation of ring polymers undergoing uniaxial elongation flow.
  • The image shows a snapshot from a molecular simulation (center) of ring polymers undergoing uniaxial elongation flow (left). No matter how slowly the fluid is elongated, a small fraction of ring polymers tie themselves together into daisy-chains that become highly stretched (right) and produce a massive increase in the fluid viscosity.
  • Low viscosity ring polymers inexplicably become highly viscous when stretched in elongation flow.
  • Molecular simulations reveal the rise in viscosity is due a small number of ring molecules linking together to form molecular daisy chains.
  • Daisy chains stretch out and act like much larger molecules, making the liquid highly viscous.
  • Knots linking the molecules untie once flow stops, returning the liquid to a low viscosity state.

Publication: O’Connor TC, Ge T, Rubinstein M, Grest GS. Topological linking drives anomalous thickening of ring polymers in weak extensional flows. Physical Review Letters. 2020 Jan 13;124(2):027801. [DOI: 10.1103/PhysRevLett.124.027801]

Funding: M. R. acknowledges financial support from National Science Foundation under Grant No. EFMA-1830957, the National Institutes of Health under Grants No. P01-HL108808, No. R01-HL136961, and No. 5UH3H L123645, and the Cystic Fibrosis Foundation. This work was supported by the Sandia Laboratory Directed Research and Development Program. This work was performed, in part, at the Center for Integrated Nanotechnologies, an Office of Science User Facility operated for the U.S. Department of Energy (DOE) Office of Science. Sandia National Laboratories is a multimission laboratory managed and operated by National Technology & Engineering Solutions of Sandia, LLC, a wholly owned subsidiary of Honeywell International, Inc., for the U.S. DOE's National Nuclear Security Administration under Contract No. DENA-0003525.