Evidence of a Sponge-to-Lamellar Phase Transition under Shear by X-Ray Scattering Experiments in a Couette Cell

The $L_3$ sponge phase under shear in a Couette cell is totally transformed to a lamellar phase $L_{{\alpha }^{*}}$ above some critical shear rate ${\dot{\gamma }}_c$. In situ x-ray scattering and simultaneous light microscopy observations show that the first nuclei of the $L_{{\alpha }^{*}}$ phase appear at a low critical shear rate ${\dot{\gamma }}_a$ and that the orientation of the lamellae in the $L_{{\alpha }^{*}}$ phase tilts over from a so-called “ $a$” orientation to a “ $c$” orientation at ${\dot{\gamma }}_c$. In the regime with two phases ${\dot{\gamma }}_a$ and ${\dot{\gamma }}_c$, the phases are in an epitaxial relationship immediately after the shear is removed.