Two-state theory of single-molecule stretching experiments

We present a statistical mechanics analysis of the finite-size elasticity of model polymers, consisting of domains that can exhibit transitions between more than one stable state at large applied force. The constant-force (Gibbs) and constant-displacement (Helmholtz) formulations of single-molecule stretching experiments are shown to converge in the thermodynamic limit. Monte Carlo simulations of continuous three-dimensional polymers of variable length are carried out, based on this formulation. We demonstrate that the experimental force-extension curves for short and long polymers are described by a unique universal model, despite the differences in chemistry and rate-dependence of transition forces. DOI: 10.1103/PhysRevE.87.032705