The structure of the nematic phase of cyano derivatives and their mixtures with weakly polar compounds

Abstract

The nematic phases of cyano derivatives of different chemical classes, in particular pyridine derivatives, and their mixtures with weakly polar matrices, 4,4′-butylmethoxyazobenzene and 4-transbutyl cyclohexanecarboxylic acid, have been investigated by X-ray diffraction over the entire concentration range. Values have been obtained for the fluctuation layer structure period, d, and the longitudinal correlation length, ζ, for two incommensurate density waves corresponding to monomers and dimers of the cyano derivatives. Specific features of the concentration behaviour of d ₁ and d ₂ depending on the structure of the cyano derivative and the weakly polar matrix have been analysed. A linear correlation between the elastic constant ratio K ₃/K ₁ and d ₂ ² for cyano derivatives has been found, as well as an anticorrelation between K ₃/K ₁, the viscoelastic ratio, n _s/K ₁, and a correlation length, ζ₁ for the mixtures. In the latter case a similar concentration behaviour of n _B/K ₃ and ζ₂ and d ₂ has been established.