Anisotropic optical properties of liquid crystals (LC), combined with their fluidity, are crucial for the development of new liquid crystal devices and applications. The optical anisotropy implies an existence of various refractive indices that depend on the direction of light oscillation relative to the director vector. For some applications, it is, however, necessary to estimate an average refractive index (n_av) for the liquid–crystalline material, which is commonly effected through models of combination of the anisotropic refractive indices. The validity of these models lacks proof as the experimental average refractive index for anisotropic fluids has not been published. This article reports an experimental strategy to measure n_av of liquid crystals; the method is based on generating multiple orientations of the liquid crystal molecules through their isotropization in mixtures with isotropic liquids. The refractive index of an isotropic mixture is measured; then the apparent refractive index of the liquid crystal is extracted using validated combination models of refractive indices in mixtures. The method was assessed with two nematic liquid crystals (5CB and MBBA) mixed with several isotropic liquids. The results indicate that the average refractive index of a LC is an extrapolation, in the nematic range of temperatures, of the index variation above the nematic–isotropic transition. A new theoretical model to predict the average refractive indices of liquid crystals was developed. Compared with the traditional formulae, the new model represents a significant improvement for the calculation of n_av.

Non-steroidal anti-inflammatory drugs are recognized widely as emerging contaminants. Sulindac has received additional attention as a prodrug in cancer treatment and because of its detection in drinking water and wastewaters. Nevertheless, there is limited knowledge about its kinetic behaviour and fate in the aquatic environment. In this work, the direct photolysis of sulindac, in which photochemical reactions were monitored and phototransformation products identified, was investigated under prolonged periods using UV-A and UV-B radiation and pH conditions (2 and 7) to evaluate the effect of the protonation state and the efficiency of the photolytic process. A novel kinetic mechanism has been proposed in which sulindac exhibits a consecutive reaction pathway, with pseudo-first order kinetics for rapid and reversible Z to E isomerization. Once photoequilibrium was reached, second-order degradation of the isomers in the presence of the new photodegradation products was observed. Photochemical transformation was faster under UV-B irradiation and lower pH, which suggests greater persistence of sulindac at more relevant environmental conditions of UV-A and pH 7. Two novel and major byproducts were identified, corresponding to the oxidative cleavage of the alkene exo to the indene system. The degradation pathway is mainly photoinduced, enhanced by acidic conditions and presumes the double bond as the most reactive site for the parent compound. This research demonstrates an approach for determining kinetics of compounds under challenging conditions, including, absorption from multiple electronic transitions, photoinduced products with unknown extinction coefficients, concentration dependence, photoinduced sensitizing intermediates, and speciation effects. Our work greatly improves our understanding of the degradation process of sulindac and will contribute to exposure assessments and treatment methodologies for this compound in impacted waters.