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