The bend elastic constant in a mixture of (4,4')-n-octyl-cyanobiphenyl and biphenyl

The effect of a rigid, non-polar and nonmesogenic solute biphenyl ((C_{6}H_{5}-C_{6}H_{5})) on the divergence of the bend elastic constant K_{33} of (4,4^{\prime}) -n-octyl-cyanobiphenyl (8CB) near the smecticA-nematic transition is reported. The exponent decreases from about 1.0 to 0.67 as the concentration of biphenyl increases. The temperature at which the divergence takes place is about 0.5 to 1.0K higher than the transition temperature T_{AN} >. A simple calculation based on Landau theory is presented to explore the possibilities of the existence of a biphenyl induced tricritical point.