Plasticity in a Smectic- A Liquid Crystal

We present direct measurements of the layer rigidity in a smectic-A liquid crystal, 4{'}-n-octyloxy-4-cyanobiphenyl. For low normal to the layers, the instantaneous induced stress is elastic and gives B=0.8×10⁷ cgs units at 60^∘{}C. In response to a steplike strain, the stress relaxes almost completely, with a time constant {~}50 ms. The relaxation stops for a residual strain smaller than {} layer over the total thickness of the smectic sample.