# Direct observation of shear-induced orientational phase coexistence in a lyotropic system using a modified X-ray surface forces apparatus Academic Article

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### abstract

• The second generation x-ray surface forces apparatus (XSFA-II) allows for the first time simultaneous in situ small-angle x-ray scattering and surface force measurements. We have used the XSFA-II to monitor shear-induced orientational transitions in a lyotropic model lubricant system. Upon applying small shear amplitudes ( $\ensuremath{\sim}20\ensuremath{\mu}\mathrm{m}$) to a relatively thick ( $\ensuremath{\sim}800\ensuremath{\mu}\mathrm{m}$) film, we observed evidence for the formation of an orientational boundary layer at the shearing surface. Time-resolved x-ray diffraction revealed the gradual transition to shear-favored orientation by growth of the boundary layer.

### publication date

• January 1, 2001