A non-standard temperature dependence of the order parameter of the 5CB liquid crystal doped with an azo-derivative

The effects of the cis and trans form of the 4-OMe-phenylazobenzene at 1% and 7% mole fraction on order, mesophase stability and dynamics of the 5CB liquid crystal were studied using the ESR spin probe technique. The presence of the trans azo-derivative induced a downshift of the nematic–isotropic transition temperature TNI which increased with the concentration but did not change the dependence of the order parameter on the reduced temperature. The cis isomer caused even larger TNI shifts, determining a marked decrease of the order parameter with a peculiar dependence the reduced temperature, quite different from the standard Haller-type behavior. The spin probe dynamics appeared instead to be essentially unchanged by the presence of the azo-derivative.