Dynamics of a semiflexible polymer or polymer ring in shear flow

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Item Type:	Article
Title:	Dynamics of a semiflexible polymer or polymer ring in shear flow
Creators Name:	Lang, P.S., Obermayer, B. and Frey, E.
Abstract:	Polymers exposed to shear flow exhibit a remarkably rich tumbling dynamics. While rigid rods rotate on Jeffery orbits, a flexible polymer stretches and coils up during tumbling. Theoretical results show that in both of these asymptotic regimes the corresponding tumbling frequency fc in a linear shear flow of strength {gamma} scales as a power law Wi2/3 in the Weissenberg number Wi={gamma}{tau}, where {tau} is a characteristic time of the polymer's relaxational dynamics. For a flexible polymer these theoretical results are well confirmed by a large body of experimental single molecule studies. However, for the intermediate semiflexible regime, especially relevant for cytoskeletal filaments like F-actin and microtubules, the situation is less clear. While recent experiments on single F-actin filaments are still interpreted within the classical Wi2/3 scaling law, theoretical results indicated deviations from it. Here we perform extensive Brownian dynamics simulations to explore the tumbling dynamics of semiflexible polymers over a broad range of shear strength and the polymer's persistence length lp. We find that the Weissenberg number alone does not suffice to fully characterize the tumbling dynamics, and the classical scaling law breaks down. Instead, both the polymer's stiffness and the shear rate are relevant control parameters. Based on our Brownian dynamics simulations we postulate that in the parameter range most relevant for cytoskeletal filaments there is a distinct scaling behavior with fc{tau}=Wi3/ 4fic(x) with Wi={gamma}{tau} with Wi={gamma}{tau}* and the scaling variable x=(lp/L)(Wi)-1/3; here {tau}* is the time the polymer's center of mass requires to diffuse its own contour length L. Comparing these results with experimental data on F-actin we find that the Wi3/4 scaling law agrees quantitatively significantly better with the data than the classical Wi2/3 law. Finally, we extend our results to single ring polymers in shear flow, and find similar results as for linear polymers with slightly different power laws.
Keywords:	Chemical Models, Computer Simulation, Diffusion, Elastic Modulus, Mechanical Stress, Molecular Models, Polymers, Rheology, Shear Strength, Statistical Models, Viscosity
Source:	Physical Review E
ISSN:	1539-3755
Publisher:	American Physical Society
Volume:	89
Number:	2
Page Range:	022606
Date:	27 February 2014
Official Publication:	https://doi.org/10.1103/PhysRevE.89.022606
PubMed:	View item in PubMed

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