A shear induced transition of lamellar alignment in a concentrated diblockcopolymer solution

The effect of shear on the alignment of the lamellar phase in a concentrate d aqueous salt solution of a poly(oxyethylene) and poly(oxybutylene) dibloc k copolymer is investigated in situ using small-angle X-ray scattering (SAX S). The alignment of the lamellae is deduced from the anisotropy of the sca ttering patterns. It is found that the orientation of the lamellae with res pect to the shear direction alters with an increase in the shear rate: the lamellae are oriented transverse to the shear direction at low shear rates, and perpendicular to the vorticity direction at high shear rates. The tran sition between the two lamellar alignments occurs at a critical shear rate in the range: 10 s(-1) < gamma(c) < 100 s(-1). (C) 1999 Elsevier Science Lt d. All rights reserved.