Small-angle neutron scattering from a polymer coil undergoing stress relaxation

Small-angle neutron scattering measurements have been made on samples of polystyrene in which the stress has been allowed to relax at a constant strain. The radii of gyration parallel and perpendicular to the stretch direction have been measured as a function of time after the strain has been applied. After an initial rapid change, the radii of gyration tend towards asymptotic values which are close to those for the undeformed chain. The deformation appears to behave as if the affine deformation theory holds only for distances separating effective crosslinks. It is proposed that after the initial change in radii of gyration the stress is relieved by reorientation of the chain segments.