Structures in a Semidilute Polymer Solution Induced under Steady Shear Flow As Studied by Small-Angle Light and Neutron Scattering

Structures induced by a steady shear flow in a semidilute polymer solution of high molecular weight deuterated polystyrene in dioctyl phthalate are investigated. By a combined use of small-angle light scattering (SALS) and small-angle neutron scattering (SANS), we are able to obtain scattering functions of the shear-induced structures over 3 orders of magnitude in wavenumber (q) and 7 orders of magnitude in intensity. The changes in the structures with shear rate (γ̇) at a given temperature and with temperature at a given γ̇ are explored. At a given temperature, the shear flow induces a structural change in the solution at γ̇ larger than a critical shear rate γ̇c, giving rise to a scattering pattern called “butterfly pattern” in the low q region of SANS, while keeping the same pattern as that in the quiescent state in the q region of SALS. As γ̇ increases, the butterfly patterns evolved not only in the low q region of SANS but also in the q region of SALS. This indicates that the shear-induced structures responsible for the butterfly pattern are developed over a wide q range (q ≤ 0.06 nm-1) with increasing γ̇. At a given γ̇ larger than γ̇c, both SALS and SANS scattering intensity increase with a decrease of temperature, indicating the shear-induced structures are more pronounced upon decreasing temperature. Especially, at the lowest temperature covered in this experiment, the scattering pattern observed in the low-q region of SANS is turned into an elliptical shape with a major axis perpendicular to the flow direction, while keeping the butterfly pattern in the SALS q region. A detailed analysis and discussion about the scattering functions are presented in the text.