Surface and Bulk Properties of Azoxyanisole

Abstract

Abstract p-Azoxyanisole has a nematic liquid crystal phase in addition to the normal isotropic liquid phase. In line with the rapid increase in interest in liquid crystals in recent years, its properties have been the subject of several investigations. As with nearly all initial explorations, however, these studies have raised questions as well as provided answers. Barrall, Porter and Johnson1 measured specific heat as a function of temperature, using differential scanning calorimetry and reported an unexpected knee in the liquid-liquid transition peak. Neumann and Sell2 studied the surface tension and density of azoxyanisole. A modified Wilhelmy technique which allowed continuous temperature scanning was used to make surface tension measurements. Temperature scanning density measurements were made by measuring the buoyancy of a glass bead suspended in the liquid from an electrobalance. Their results showed a step decrease at the liquid-liquid transition in both surface tension and density on heating. A split peak of the nature of that reported by Barrall; Porter and Johnson1 was observed but not reported. Meanwhile, Robinder and Poirier3 carried out a study of the solid phase of the same substance. They reported the existence of three crystalline solid phases, one of which had not been observed previously. More recently, Chow and Martire4 reported dsc heats of the transition for the nematic-isotropic transition in close agreement with those of Barrall et al.1 as well as those obtained by Arnold5 who used conventional calorimetry. They observed only two solid phases, however. There seems, therefore, ample reason to attempt to obtain more detailed information regarding both the liquid-liquid and solid-solid transitions in azoxyanisole.