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

Abstract

The ${L}_{3}$ sponge phase under shear in a Couette cell is totally transformed to a lamellar phase ${L}_{{\ensuremath{\alpha}}^{*}}$ above some critical shear rate ${\stackrel{\ifmmode \dot{}\else \.{}\fi{}}{\ensuremath{\gamma}}}_{c}$. In situ x-ray scattering and simultaneous light microscopy observations show that the first nuclei of the ${L}_{{\ensuremath{\alpha}}^{*}}$ phase appear at a low critical shear rate ${\stackrel{\ifmmode \dot{}\else \.{}\fi{}}{\ensuremath{\gamma}}}_{a}$ and that the orientation of the lamellae in the ${L}_{{\ensuremath{\alpha}}^{*}}$ phase tilts over from a so-called `` $a$'' orientation to a `` $c$'' orientation at ${\stackrel{\ifmmode \dot{}\else \.{}\fi{}}{\ensuremath{\gamma}}}_{c}$. In the regime with two phases ${\stackrel{\ifmmode \dot{}\else \.{}\fi{}}{\ensuremath{\gamma}}}_{a}$ and ${\stackrel{\ifmmode \dot{}\else \.{}\fi{}}{\ensuremath{\gamma}}}_{c}$, the phases are in an epitaxial relationship immediately after the shear is removed.