SEMIDILUTE 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 gamma . tau(c) > 1, with tau(c) being the longest relaxation time of the system. Temperature was varied from T = 13-55-degrees-C at rest and chosen at T = 25, 30 and 50-degrees-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.