Refractive Indices, Order Parameter and Optical Transmittance Studies of a Nematic Liquid Crystal Mixture

Abstract

Measurements of ordinary refractive index, birefringence, density, and order parameter were made on a technologically important nematogen and the data obtained for its nematic and isotropic phase were reported. A modified wedge method was used for the measurement of the birefringence (δn). The nematic-isotropic phase transition temperature matches very well as is exhibited from the value of refractive indices and densities obtained using different techniques. The optical anisotropy and density data were used to determine the order parameter and principal polarizability of the nematic mixture using the Vuks approach and their temperature dependence was discussed. The macroscopic order parameter was obtained and compared with microscopic order parameter. These two values agree very well.

Study of optical parameters of two fluorinated isothiocyanato nematic liquid crystals exhibiting high birefringence

“…The effect of temperature on the refractive indices and birefringence is critically important for display devices. In order to establish a relationship of the temperature dependence of LC refractive indices, various theoretical models [6][7][8][9], as well as several experimental techniques [10][11][12][13][14] have been developed. From the study of refractive indices of liquid crystals, it is possible to obtain information on anisotropy of the light waves traversing through them [15].…”

“…S is called the micro− scopic order parameter because it describes the average re− sponse of a LC molecule [22]. The macroscopic order pa− rameter Q determined from various bulk tensorial proper− ties differ among themselves and also from the micro− scopic order parameter S [13,[18][19][20][21]. This inconsistency arises possibly because of the effect of a local field which is different for different properties.…”

“…However, assuming the validity of a local field model, the microscopic order pa− rameter can be determined from the knowledge of macro− scopic bulk tensorial properties [17,18]. Several methods have been developed for the measurement of macroscopic order parameter (Q) in a LC [13,14,16,[18][19][20][21]. Measure− ment of optical anisotropy, i.e., Dn provides not only the most simplest and convenient, but also yields direct and very precise results [13,21].…”

“…Several methods have been developed for the measurement of macroscopic order parameter (Q) in a LC [13,14,16,[18][19][20][21]. Measure− ment of optical anisotropy, i.e., Dn provides not only the most simplest and convenient, but also yields direct and very precise results [13,21]. Thus, the optical methods are most frequently used for the calculation of order parameter of LCs [14,24].…”

Tunability of discrete diffraction in photonic liquid crystal fibres

“…In the second stage of numerical analy− ses the macroscopic order parameter Q (changing with tem− perature in real conditions) has been taken as a variable. In order to mimic the deviation from the ideal planar align− ment, refractive index of LC (for any direction of linear polarization) taken for simulations has been calculated with use of the formula: n o,eff = Ô + 2QDn/3, where Ô is an aver− age refractive index and Dn is the birefringence correspond− ing to the complete alignment [41]. The values of the latter two were taken as ones for the wavelength of 1064 nm at 20°C [(see Fig.…”