A Small-Angle Neutron-Scattering Study of Shear-Induced Ordering in the Cubic Phase of a Block Copolymer Gel

The structure of a diblock copolymer gel subjected to steady shearing has been examined using small-angle neutron scattering (SANS). The poly(oxyethylene) (E)−poly(oxybutylene) (B) diblock E 86 B 10 was found to form a body-centered cubic phase in 0.2 M K 2 SO 4 with a polymer concentration 30 wt % at room temperature. Above a critical shear rate in the range γ = 50−500 s - 1, the sample became macroscopically oriented into a polydomain structure with a [111] direction of the bcc unit cell along the shear direction. The SANS patterns obtained at high shear rates contained reflections from the {110} and {211} planes that intersect along a common [111] direction. Even at the highest shear rate employed, γ = 2.5 × 10 4 s - 1, complete shear melting was not observed (i.e., residual order was present in the SANS pattern).