Birefringence from Periodic Shear Flow near the Critical Point

The flow birefringence in the binary liquid mixture 2, 6-lutidine and water is measured near its critical point. The effect was produced by periodic variation of the shear, $S=\frac{\partial v_x}{\partial y}$, at an angular frequency, ${\omega }_0$, of 7.5 ${\sec }^{-1\mathrm{}}$, whereas typical average values of $S$ were 10 ${\sec }^{-1\mathrm{}}$. Measurements of the temperature dependence of the birefringence phase shift, $\delta$, are in fair agreement with a steady-state theory of Onuki and Kawasaki.