Polymer coil relaxation in uniaxially strained polystyrene observed by small angle neutron scattering

Measurements are reported on the static form factor of the chains in a bulk amorphous unbranched polystyrene sample, Mw ∼ 650 000, relaxing after an extensional step strain held constant at a factor 3. The temperature of deformation and subsequent relaxation was above Tg and varied from 113°C to 134 °C. Times of relaxation ranged from 10 s to 30 min. For the lowest temperatures and shortest times, the transverse radius of gyration, which is the largest characteristic length obtained from the neutron scattering data, showed a value affine with the macroscopic deformation. Time-temperature superposition is used to obtain the variation of the form factor over a wide range of reduced time. Its subsequent behaviour is compared with reptation theory predictions. In the range of intermediate wavevectors, at high temperatures, the scattered intensities measured in the longitudinal direction for different times are consistent with a universal function of reduced wavevector q/q* where (q*)4 is proportional to the relaxation duration. This behaviour was predicted by Daoudi in a study of disengagement by reptation. Its interpretation should be rediscussed