4-cyano-4 -n-pentylbiphenyl

The addition of optically active bridged biaryl molecules such as 169a-d to nematic mesophases like, e.g. 4-cyano-4 -n-pentylbiphenyl or a mixture of cyclohexane derivatives (ZLT 1167), leads to an induction of cholesteric mesophases... 

Evidence for the existence of such equilibria comes from the eight-line spectrum obtained for the parent compound in 4-cyano-4 -n-pentylbiphenyl, an inert liquid crystal. Bailey and Yesinowski found the only tenable rationalization for the fewer than expected 12-line spectrum was a rapid intramolecular rotation of one chelate ring with respect to the other, amounting to a degenerate cis-trans isomerization. 

The nematic phase is the simplest of the thermotropic liquid crystalline phases and is characterized by just one important feature All of the molecules in the material tend to align in the same direction (indicated by the director Figure 2.3). Nematic materials are the most fluid-like of the thermotropic phases with a relatively low viscosity. In a material that exhibits several thermotropic liquid crystalline phases, the nematic phase is typically found at higher temperatures, just below the isotropic liquid phase. In Figure 2.4, we can see the molecular structure for 5CB (4-cyano-4-n-pentylbiphenyl), the first room temperature nematic material developed by George Gray at Hull University in 1972. 

FIGURE 2.4 The molecular structure of an early and well-known nematic liquid crystal 5CB (4-cyano-4-n-pentylbiphenyl). 

Following this premise, PDLC systems were prepared using PVAB as a matrix and a nematic (4-cyano-4 -pentylbiphenyl 5CB) or a smectic (butyl-p-[p -n-octyloxy benzoyloxyjbenzoate) Sm liquid crystal. 

Cj-Cio n-alkanes (5) C5-C10 branched alkanes (9) benzene, toluene, xylenes (3) A-(p-methoxybenzylidene)-p -,j-butylaniline MBBA (N, I) 4-cyano-4 -pentylbiphenyl (N, 1) [545]... 

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