Toroidal condensates of semiflexible polymers in poor solvents: adsorption, stretching, and compression

When a semiflexible polymer chain is placed in a poor solvent, or in the pr esence of condensing agents, a toroidal condensate can result. In typical e xperiments, these condensates are adsorbed to surfaces. Here we examine the changes that can occur when a toroid is adsorbed. We then examine the beha vior of a toroid when stretched and identify two regimes: a weak stretching regime where the toroid deforms from a circle to an ellipse, and a strong stretching regime where a tether is pulled from the toroid. In the weak str etching regime, the force increases linearly with separation whereas in the strong stretching regime, the applied force is a constant. We then look at the case of a toroid compressed in the plane of the toroid. In this case t he form of the force law depends on how strongly the toroid wets the surfac es. In general, an inverse square force law is found.