Shear induced phase inversion of dilute smectic liquid crystal/polymer blends

Abstract

The rheology and morphology of 8CB (4-octyl-4-biphenylcarbonitrile) and PDMS (polydimethylsiloxane) blends with different concentrations of 8CB were investigated. The blends showed gel-like behaviour when 8CB is in the smectic state during mixing, whose morphologies resemble the foam-like structure of a highly concentrated emulsion with 8CB as the continuous phase. Once formed, such a structure is stable when 8CB is in a smectic and nematic state but unstable when 8CB is in an isotropic state. The stability of the foam-like structure is ascribed to the elasticity of 8CB films, which is justified by the concentration dependence of the interfacial contribution to the plateau modulus, i.e., the yield stress of 8CB instead of the Laplace pressure controls the deformation of the PDMS droplet. A new mechanism of phase inversion is suggested based on the direct observation of the breakup mode of an 8CB droplet. The formation of the foam-like structure was the result of the erosion breakup of the 8CB droplets and the subsequent local phase inversion, where the erosion breakup is ascribed to the shear banding inside the droplet due to the yield stress of 8CB in the smectic state.