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Theoretical Prediction for Ring Polymers under Shear Experimentally Confirmed

Jülich/Vienna/Illinois/San Diego,

20 November 2020

The phenomenon of “vorticity swelling” was discovered in 2018 by scientists from the University of Vienna  and Forschungszentrum Jülich using computer simulations. It describes a swelling of ring-shaped polymers that occurs under shear stress. An experiment by US researchers at the University of Illinois now confirms that vorticity swelling actually occurs in reality: rings under shear stress behave exactly as predicted in theory.

Theoretical Physics Flow field of the solvent at the flow-vorticity level around the polymer as predicted by simulation. Velocities are encoded by colour, flow lines indicate direction. A typical polymer ring configuration is shown to indicate the position of the ring relative to the flow field.
Copyright: Christos Likos/University of Vienna

In 2018, PD Dr. Marisol Ripoll from Forschungszentrum Jülich and Maximilian Liebetreu and Prof. Dr. Christos Likos from the University of Vienna discovered by means of simulation that, when ring polymers are subjected to shear stress, the backflow of the solvent and the ring topology lead to a polymer behaviour which had not been previously encountered and which was not known to occur in any other polymer. This is a clear increase of the ring size in the direction perpendicular to both the flow and velocity gradient – the so-called vorticity direction, after which the phenomenon they discovered was named: vorticity swelling. The phenomenon was new and unexpected, but the evidence gained from theory and simulation was compelling.

Much to the delight of Marisol Ripoll and her Vienna-based theorist colleagues, experimental physicists from the US universities of Illinois and San Diego have now confirmed the theoretical findings. Similar to the setup simulated by the researchers from Jülich and Vienna in 2018, the researchers from the USA used fluorescence-labelled DNA rings and built custom-made shear flow apparatus to analyse in detail the shapes and conformations of ring polymers under shear flow.

Original publication:

M. Tu, M. Lee, R. M. Robertson-Anderson und C. M. Schroeder;
Direct Observation of Ring Polymer Dynamics in the Flow-Gradient Plane of Shear Flow;
Macromolecules (2020).

Maximilian Liebetreu, Marisol Ripoll und Christos N. Likos;
Trefoil Knot Hydrodynamic Delocalization on Sheared Ring Polymers;
ACS Macro Letters 2018

Further information:

Press release University of Vienna "Experimente bestätigen Theorie zu Ringpolymeren unter Scherung" (in German) from 3 November 2020

News item from the Faculty of Physics, University of Vienna “Prediction of Viennese theorists on sheared ring polymers experimentally confirmed by US scientists” from 3 November 2020:

Press release University of Vienna “Loose or Tight: When Knots Sit on Polymer Rings” from 26 March 2018

Home page of the Young Investigators Group of Dr.Ripoll at  the Institute of Biological Information Processing – Theoretical Physics of Living Matter (IBI-5/IAS-2)

Home page of the Likos research group at the University of Vienna

Home page of the Schroeder group at the University of Illinois


PD Dr. Marisol Ripoll
Institute of Biological Information Processing –
Theoretical Physics of Living Matter (IBI-5/IAS-2)
Forschungszentrum Jülich
Tel: +49 2461/61-5773

Press contact:

Angela Wenzik, Science Journalist
Forschungszentrum Jülich
Tel: +49 2461 61-6048