Effective Geometry Parameter Research Articles

Order parameter studies from effective order geometry in 4O.Om and 7O.Om liquid crystalline compounds

The effective geometry parameter, αg = n o /n e, is used to evaluate the orientational order parameter, S, in the case of N-(p-n-butyloxybenzylidene)-p-n-alkoxy anilines, 4O.Om and N-(p-n-heptyloxybenzylidene)-p-n-alkoxy anilines, 7O.Om compounds with m = 3–7 and 9 in the former case and m = 3, 5–7 and 9 in the later materials. The results obtained are compared with those calculated using the standard techniques of molecular polarisability and birefringence. The effective geometry parameter's influence on the deflection of light by the liquid crystal compounds is also studied. The variation of temperature gradient of the ordinary refractive index, dn o /dT, and extraordinary refractive index, dn e /dT, of the liquid crystals is also studied.

Determination of orientational order and effective geometry parameter from refractive indices of some nematics

Orientational order parameter and effective geometry parameter have been calculated from the refractive indices of four nematic liquid crystals (LCs). A modified four-parameter model is used to fit the experimental data of temperature-dependent ordinary and extraordinary refractive indices. This four-parameter model can be approximated as a three-parameter model for low-birefringence and high-clearing temperature LCs. Experimental data of a specific LC sample ( ∼ 0.08 and T c = 155°C) have been used to validate the three-parameter model. The behaviour of effective geometry parameter as a function of temperature and order parameter has also been reported. Different methods of order parameter determination from optical data are compared. The order parameter is calculated by using Haller, Vuks and Neugebauer equations. In addition, an equation describing order parameter in terms of effective geometry parameter is also used to calculate the order parameter. Modified four-parameter model is applied to fit the experimental data of effective geometry parameter and also to fit the order parameter determined by using four different methods. For all the parameters we studied, a very good agreement between theory and experiment is obtained.

Order parameter studies from effective order geometry in a number of liquid crystals of different homologous series

The effective geometry parameter, αg=no/ne is utilized to calculate the order parameter in a number of liquid crystals of different homologous series. The results are compared with those calculated using the standard techniques of molecular polarizability and birefringence. The effective geometry parameter's, αg influence on the deflection of the light by the liquid crystal compounds is also studied.

Order parameter studies on EPAP alkanoate mesogens

The refractive indices of p(p-ethoxyphenylazo) phenyl (EPAP) alkanoates, which are the nematic liquid crystals where the alkyl chain n is 5, 6, 7 and 11, were measured as a function of temperature at λ = 6328 Å using a wedge technique. The temperature variation of the orientational order parameter (S) is calculated at this wavelength using the Vuks model (with consideration of internal field) and by different methods excluding the internal field – Haller and Kuczynski models, and involving effective geometry parameter (αg). The intensity of light deflection in a uniaxial EPAP alkanoate with a particular molecular configuration and ordering by varying temperature is discussed. The temperature gradients of the ordinary (∂no /∂T) and extraordinary (∂ne /∂T) refractive indices are analysed. Due to a high clearing temperature with low molecular chain length, EPAP valerate exhibited low deviation of light with a large positive value of ∂no /∂T.

Investigations into effective order geometry in a series of liquid crystals

The effect of temperature variations on refractive index and molecular polarisability have been studied in liquid crystals based either on p,p′-alkoxyazoxybenzene derivatives, in which the alkyl group is n-pentyl or n-heptyl, or on p-alkoxybenzoic acids, in which it is n-hexyl or n-nonyl. The order parameter has been calculated using the Vuks, Neugebauer and Wu-modified equations, and also from birefringence measurements. In addition, an order parameter equation involving the effective geometry parameter has been derived and its influence on the deflection of light by the liquid crystalline compounds studied. At low temperatures, and at high values of order parameter and birefringence, the effective geometry parameter was low. In the light of the results obtained, a comparison of the order parameter derived by various methods is presented. The temperature variation of temperature gradient of the ordinary refractive index, dno /dT, and extraordinary refractive index, dne /dT, of the liquid crystals are shown. Among the compounds studied, p-n-heptyl–p′-azoxybenzene produced a large value for dno /dT, due to its lower clearing temperature.