Splay and bend elastic constants and rotational viscosity coefficient in a mixture of 4-4'-n-pentyl-cyanobiphenyl and 4-4'-n-decyl-cyanobiphenyl

Measurement of splay, bend elastic constants and rotational viscosity coefficient in mixtures of 4-4'-n-pentyl-cyanobiphenyl (5CB) and 4-4'-n-decyl-cyanobiphenyl (10CB) are reported. The mixture exhibits smectic A and nematic phases. The bend elastic constant and the rotational viscosity coefficient diverge as the smectic A phase is approached from the nematic side and we have determined the exponents for divergence of these two quantities. Both exponents seem to depend on the relative concentration of the constituents in the mixtures, and the values for the bend elastic constant show a jump from 0.7 to 1.0 when the mole fraction of 5CB increases from 0.25 to 0.30. This is consistent with the presence of a tricritical point for the phase transition. The possibility of the existence of a smectic A-vector nematic tricritical point is discussed in the framework of Landau theory