Force induced conformational transition in a system of interacting stiff polymer: Application to unfolding

We consider a stiff polymer chain in poor solvent and apply a force at one end of the chain. We find that by varying the stiffness parameter, polymer undergoes a transition from the globule state to the folded like state. The conformation of folded state mimics the $\beta$-sheet as seen in titin molecule. Using exact enumeration technique, we study the extension-force and force-temperature diagrams of such a system. Force-temperature diagram shows the re-entrance behaviour for flexible chain. However, for stiff chain this re-entrance behaviour is absent and there is an enhancement in $\theta$-temperature with the rise of stiffness. We further propose that the internal information about the frozen structure of polymer can be read from the distribution of end-to-end distance which shows saw-tooth like behaviour.