Semi-Dilute Polymer Solutions under Shear

Small-angle neutron scattering (SANS) experiments have been performed on a semi-dilute polymer solution at rest and in laminar shear flow under a constant shear gradient in the range · τc > 1, with τc being the longest relaxation time of the system. Temperature was varied from T = 13-55°C at rest and chosen at T = 25, 30 and 50°C for the measurements under shear, hence the theta solvent regime as well as the good-solvent regime are explored. An anisotropy of the two-dimensional scattering pattern is observed under shear at all temperatures, with an increase of the low q scattering in the direction parallel to the flow. The corresponding double winged shape of the pattern resembles the "butterfly" shapes found for the interchain scattering in deformed gels and rubbers. Spontaneous fluctuation as well as frozen fluctuation models may both be compared with the results.