Rheological properties smectic liquid crystals

Figure 5.132 illustrates that mesophases can also be identified by rheological properties. The crystals of PTFE show a highly anisotropic flow parallel to the molecular axes, a property often found in smectic liquid crystals. As soon as the molecules start to melt, however, the shear-stress increases abruptly because of the chain-entanglement that occurs during melting. On a microscopic basis, PTFE... 

On a microscopic scale just as for low molecular weight liquid crystals, nematic and cholesteric mesophases have been identified. Whether the smectic structure actually exists for polymeric systems is still open to question. However, it seems to be the macroscopic structure which accounts for the rheological properties of LCP. 

Here ri r]c is the relevant Miesovicz viscosity, and v is the velocity of the sphere. The situation is quite different for semi-infinite and finite barriers, where permeation is necessarily involved in the flow, leading to undulation of layers and arrays of defects. Since it is very difficult to trap and stabilize a sphere vdth a size smaller than the film thickness, as far as we know, the flow of smectics aroimd a sphere has never been studied experimentally. However, experiments when finite particles are moving in the liquid crystal medium, which is at rest far from the particles has been carried out very recently, and it was indeed found that the flow of beads in smectic A and smectic C liquid crystals is purely viscous at sufficiently high speeds. Such technique is analogous to the one-bead micro-rheology ° developed recently to monitor the mechanical properties of viscoelastic soft materials, especially biological systems. i... 

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