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Soft Matter and Biological Physics

Eur. Phys. J. E 5, 391-402 (2001)

Shear-induced ordering of lamellar and gyroid structures observed in a nonionic surfactant/water system

M. Imai1, K. Nakaya1 and T. Kato1, 2

1  Department of Physics, Faculty of Science, Ochanomizu University, Bunkyo, Tokyo 112-0012, Japan
2  Graduate School of Science, Tokyo Metropolitan University, Hachioji, Tokyo 192-0397, Japan


(Received 26 June 2000 and Received in final form 12 January 2001 )

The shear-induced ordering of lamellar and gyroid structures of a nonionic surfactant C16E7/D2O system in a Couette shear cell ( $0.001 < \dot{\gamma} < 10$ s-1, $\dot{\gamma}$: shear rate) has been investigated by using a small angle neutron scattering technique. In the lamellar phase, the steady shear flow having $\dot{\gamma} > 0.01$ s-1 suppresses undulation fluctuations of lamellae (Maxwell effect). This suppression of fluctuations brings two effects; 1) shear-induced lamellae ordering toward a parallel orientation and 2) obstruction of a lamellar$\to$gyroid transition. It is quite interesting to note that there is a characteristic shear rate range ( $0.01 < \dot{\gamma} < 0.3$ s-1), where both effects take place. We have also investigated the shear effects on the gyroid phase. Below the characteristic shear rate range, the gyroid structure keeps three-dimensional network lattice, while above the characteristic shear rate range, the gyroid structure transforms to the parallel orientation lamellae (shear-induced gyroid-lamellar transition). Thus the shear flow having the characteristic shear rate plays very important roles in shear ordering phenomena.

83.50.Ax - Steady shear flows, viscometric flow.
68.55.Jk - Structure and morphology; thickness; crystalline orientation and texture.
64.70.Md - Transitions in liquid crystals.

© EDP Sciences, Società Italiana di Fisica, Springer-Verlag 2001