Charged, semi-flexible polymers under incompatible solvent conditions

Biological polymers such as F-actin and DNA form toroidal conformations under poor solvent conditions. This has been predicted using a model based on the polymer’s stiffness and the solvent conditions. However it is well known these polymers are highly charged. We therefore include the presence of charge along the polymer in our model and compare the energies of a single toroid versus a double toroid. Unlike the fully-flexible polyelectrolyte case we show that the toroid does not undergo a Rayleigh instability (i.e. the fission of a liquid droplet due to excess charge), which has important ramifications for the recently observed rings-on-a-string structure.