EFFECT OF QUASISPHERICAL SOLUTES ON THE NEMATIC TO ISOTROPIC TRANSITION IN 7CB.

Density as a function of temperature was measured in the nematic and isotropic phases of p-n-heptyl-p prime -cyanobiphenyl (7CB). Similar measurements were made on dilute solutions of the quasispherical solutes Et//4C(tetraethylmethane) and R//4Sn (R equals C//2H//5, n-C//3H//7 and n-C//4H//9) in 7CB. Addition of these solutes to 7CB led, as expected, to a depression in its nematic-isotropic (NI) transition temperature and to the formation of a two-phase region. From these density measurements, beta //N and beta //I, the moduli of the slopes of the nematic and isotropic boundary lines in the reduced NI transition temperature (T*) vs solute mole fraction (x//2) diagrams, were obtained. These thermodynamic results are contrasted with values for the same solutes in p-n-pentyl-p prime -cyanobiphenyl (5CB). Indications that a curvature may exist at very low solute mole fractions in the T* vs x//2 diagram are discussed.