Steady Shearing Flow of Defect-Ridden Smectics

6 Steady Shearing Flow of Defect-Ridden Smectics 

The introduction of defects into a smectic sample destroys its fluidity. This contrasts markedly with nematics, for which the presence of defects hardly alters the fluid s viscosity. Of course, this is because in a smectic the direction locally perpendicular to the layers is solid-like, and when defects are present, all directions acquire some solid-like character. Horn and Kleman (1978) measured shearing stresses in defect-containing smectic samples of 8CB and found that the shear stress was given by the equation of a Bingham plastic  

When there are no defects in the sample, A 0 and B is then the viscosity of the smectic in orientation b. Both A and B were found to increase as the number of defects in the sample increases. A is an elastic yield stress of a defect-containing smectic. The magnitude of A can can be estimated from the density of smectic defects as 

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