On the deformation of spontaneously twisted fluctuating ribbons

Abstract

A theoretical analysis of the effect of force and torque on spontaneously twisted, fluctuating elastic ribbons is presented. We find that when a filament with a straight center line and a spontaneously twisted noncircular cross section is subjected to a sufficiently strong extensional force, its average elongation exhibits an asymmetric response to large over and undertwist. We construct the stability diagram that describes the buckling transition of such ribbons under the opposing action of force and torque and show that all the predicted behaviors can be understood in terms of continuous transformations between straight and spiral/helical states of the ribbon. The relation between our results and experimental observations on DNA is discussed and a new reentrant spiral to rod transition is predicted at intermediate values of twist rigidity and applied force.