Synopsis: Entangled in tubes

Constrained polymer strands have unusual mechanical properties when they are distorted.
Synopsis figure
Illustration: B. Wang et al., Phys. Rev. Lett. (2010)

Despite considerable theoretical work, experiments on long chain macromolecules—the diffusion properties of which determine how substances ranging from plastics to cell cytoskeletons behave—have been hard to come by.

In a paper appearing in Physical Review Letters, Bo Wang and colleagues at the University of Illinois in Urbana, US, present measurements of the Brownian motion of molecules that are confined by a harmonic potential to a tubelike region. With single-molecule fluorescence microscopy, they are able to track molecules on polymer networks. They find a surprisingly large regime where the restoring force on a polymer is independent of its displacement. Though their work does not address local space- and time-dependent characteristics of these polymers, they hope that others will look more closely at how distributions, as opposed to more smeared out “averages,” play an important role. – Sami Mitra


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