Effect of properties of the smectic Adphase on the induction of a nematic phase in binary mixtures of smectics A1and Ad

The phase diagrams of two series of binary mixtures composed of 5-trans-n-butyl-2-(4-isothiocyanatophenyl)-1,3-dioxane (smectic A1) and 4-(trans-4′-n-alkyl-cyclohexyl)-1-(2-cyano-ethenyl)benzene or 4-cyanophenyl-4′-n-alkoxybenzoates (both smectic Ad) are determined. It is shown that the smectic layer spacing ratio and smectic phase transition enthalpy are the factors influencing the width and the position of the nematic gap created between the two smectic regions. It is found that their influence on this ability is in the opposite direction.