Shear effects on a nonionic lyotropic smectic liquid crystal has been studied by the simultaneous measurements of the structure factor and the viscosity, in a hyperswollen regime. We have found that (i) the flow behavior of the smectic phase is intrinsically non-Newtonian and (ii) the shear flow decreases the average interlayer spacing and increases the layer displacement fluctuations. The behavior could be explained by the following physical picture: The shear flow causes the elastic deformation of the fluctuating membranes. The resulting suppression of the fluctuations leads to the increase in the number density of layers and the weakening of the steric repulsion.

• Received 6 June 1994

DOI:https://doi.org/10.1103/PhysRevLett.74.932