Influence of an Electric Field on the Dielectric Loss of the Liquid Crystal p-Azoxyanisole

Abstract

This work involves the alignment of molecules in the anisotropic liquid phase of p-azoxyanisole due to externally applied dc and ac electric fields and walls of the sample holder. Microwave techniques involving dielectric measurements are used to provide a measure of the alignment. Results are discussed which suggest that for very pure samples an alignment should be produced with the long axes of the molecules perpendicular to the externally applied electric field. The alignment with the long axes parallel to the external field which is often observed appears to be due to an extremely small amount of impurity. This alignment appears to be associated with the conductivity, with an alignment produced such that the conductivity is a maximum in the direction of the field. Results are also discussed which suggest that small amounts of impurity are effective in producing an alignment of the molecules parallel to the walls of the sample holder.

Biaxial Micelles in a Uniaxial Nematic Phase. An Angular-Dependent 23Na NMR Study

“…Since the director of the phase spontaneously aligns with the magnetic field, such experiments are somewhat tricky to perform. Several procedures have been developed to overcome this problem; e.g., slow rotation of the sample tube around an axis perpendicular to the magnetic field, , fast spinning of the sample tube around an axis at the angle θ LD to the magnetic field, or use of an electric field. − Since in the present system the anisotropy of the diamagnetic susceptibility of the phase is only slight, the magnetic torque that tends to orient the director with the field is small. In addition, the rotational viscosity of the phase is so high that the reorientation of the director is a fairly slow process (lasting for minutes).…”

Electrohydrodynamic Convection Instabilities Observed in Suspensions of Cellulose Nanocrystals

“…However, these instabilities have been broadly studied in the past century on molecular liquid crystals in a very different geometry, whereby the field is applied parallel in the direction of highest confinement, parallel to the viewing direction by using transparent electrodes, and the variety of patterns observed in this configuration already justified an effort of classification. (Blinov et al 1982;Blinov 1986Blinov , 1998 The physical interpretation of the underlying mechanisms for this instability is usually captured by the now standard Carr-Helfrich mechanism, (Carr 1963;Helfrich 1969) which was successfully described theoretically (Dubois-Violette et al 1971;Smith et al 1975) and confirmed by experiments. (Orsay Liquid Crystal Group 1970) It is usually divided in a conductive regime at lower frequencies and a dielectric regime at higher frequencies.…”

Poisson–Boltzmann equation and electro-convective instability in ferroelectric liquid crystals: a mean-field approach

“…The origin of this term lies in the early work of Carr in 1963 [37], in which conduction-induced alignment in nematic liquid crystal was studied extensively. It was suggested that the long molecular axes undergo a specific alignment parallel to the walls of the container due to the presence of impurities in the samples.…”