Flow mechanisms in the face-centred cubic micellar gel of a diblock copolymer

The mechanisms of flow of a face-centred cubic micellar phase were investig ated using small-angle X-ray scattering (SAXS) for samples under either ste ady or oscillatory shear in two different geometries: Couette cell and plan ar shear sandwich. The system studied was a gel formed by a poly(oxyethylen e)poly (oxypropylene) diblock copolymer in water. SAXS indicated that under steady shear in a Couette cell, flow occurs via sliding of hexagonal close -packed (hep) layers with a close-packed [110] direction along the shear di rection. Under oscillatory shear in the planar shear sandwich, coexistence between this orientation and one in which the hep layers are rotated by 30 degrees (and flow is in a [211] direction) was observed; however, when subj ect to oscillatory shear in the Couette cell, flow only occurred along a [1 10] direction. This observation of flow in a non-close-packed direction may be due to alignment induced by the walls of the shear sandwich.