FORCE-LENGTH RELATIONS IN DEFORMED COILS ABOVE AND BELOW THE THETA-STATE - POSSIBLE BIMODALITY IN THE CHAIN DISTRIBUTION FUNCTION

Stretching of flexible macromolecules by an external force, acting on the chain ends, in solvents of variable quality was simulated by the Monte Carlo method on a tetrahedral lattice. The force-length relations and the stress-induced changes in the population of the gauche conformers were calculated for coils in theta and athermal solvents. In poor solvents, the stretching of a collapsed coil involves a rather abrupt upturn of the force-length curve explained as a transition of a globular coil into an extended coil. In conformity with this interpretation, a bimodal shape of the chain vector distribution function P(R) was found in the intermediate range of deformation of collapsed coils. The significance of the results to the stress-strain behavior of networks with pronounced interaction (such as collapsed gels) are discussed.