Study of the physical properties of an ester/biphenyl mixture, exhibiting an injected smectic phase, by small-angle x-ray diffraction

Abstract

Small angle x-ray diffraction intensities from binary mixtures of 4-n-pentyl 4′cyanobiphenyl (5CB) and 4-n pentyl phenyl 4-n′ hexyloxy benzoate (ME60.5), which show an injected smectic phase, have been analysed to determine the orientational order parameters (P ₂) and (P ₄), the translational order parameter, the layer thickness in the smectic phase, and the apparent molecular length in the nematic phase. The order parameters have been fitted satisfactorily to those calculated from McMillan's theory by varying the potential parameters α and [sgrave]. The experimental variation of the layer thickness with mole fraction of 5CB has been explained fairly well by assuming the presence of both homo dimers (5CB + 5CB) and hetero dimers (5CB + ME 60.5) in the mixture. Orientational order parameters, layer thickness, and packing fraction all exhibit minima at about 50% molar concentration of 5CB.

Key Words:

• Injected smectic phase
• x-ray diffraction
• order parameters
• binary mixture
• layer thickness
• packing fraction