Confinement liquid crystals, smectic phase

Multilamellar bilayers in the fluid phase are also ordered in the sense that they are smectic liquid crystals. Of great interest is the range of molecular order this is long-range in the sense that the molecules are confined to two dimensions there is also some kind of short-range order in molecular orientations and conformations, but the range of this latter ordering is not known at present. 

By measuring the surface forces one can therefore obtain important information not only on the structure of a liquid crystal, but also on the influence of confining surfaces on orientational and positional ordering on a molecular level. This Chapter describes experimental techniques that are used for the measurements of surface forces and is focused on the results of the experiments that have been recently performed in the isotropic, nematic and smectic-A phases. 

I. 1. Smalyukh, N.A. Clark, Organization of the polarization splay modulated smectic liquid crystal phase by topographic confinement. Proc. Nat. Acad. Sci. USA 107, 21311-21315 (2010)... 

In condensed matter physics, the effects of disorder, defects, and impurities are relevant for many materials properties hence their understanding is of utmost importance. The effects of randomness and disorder can be dramatic and have been investigated for a variety of systems covering a wide field of complex phenomena [109]. Examples include the pinning of an Abrikosov flux vortex lattice by impurities in superconductors [110], disorder in Ising magnets [111], superfluid transitions of He in a porous medium [112], and phase transitions in randomly confined smectic liquid crystals [113, 114]. 

As one example. Figure 10.4 shows results obtained with octyl-cyanobiphenyl (8CB, Hi7C8(C6H4)2CN). At high temperature, 8CB is an isotropic liquid. When it is cooled slowly to 40.5 °C, the material becomes a nematic liquid crystal, where the molecules align and show a preferred orientation. Cooling further to 33.5 C, 8CB undergoes a phase transition from smectic to nematic, where in addition to the orientational order the molecules form a layered structure. 8CB forms solid crystals when the temperature is reduced below 21.5 °C. When confined between two... 

---