Elasticity of smectic liquid crystals with focal conic domains.

We study the elastic properties of thermotropic smectic liquid crystals with focal conic domains (FCDs). After the application of the controlled preshear at different temperatures, we independently measure the shear modulus G' and the FCD size L. We find out that these quantities are related by the scaling relation G' ≈ γ(eff)/L, where γ(eff) is the effective surface tension of the FCDs. The experimentally obtained value of γ(eff) shows the same scaling as the effective surface tension of the layered systems √(KB), where K and B are the bending modulus and the layer compression modulus, respectively. The similarity of this scaling relation to that of the surfactant onion phase suggests an universal rheological behavior of the layered systems with defects.