Thermal, optical, and volumetric studies on mixing properties of binary nematic mixtures of 9CHBT/11CHBT

Abstract

• Phase diagrams of a series of binary nematic mixtures (9CHBT/11CHBT) were studied by DSC method. • The modified four-parameter model was used by fitting the experimental data. • The temperature dependence of refractive indices, birefringence and order parameters in nematic phase was investigated. • Quantum chemical calculations on the nematogens provide supportive picture of the optical measurements. Phase diagrams and optical properties of a series of nematic binary mixtures composed of 4-(trans-4′-n-nonylcyclohexyl) isothiocyanatobenzen (9CHBT) and 4-(trans-4′-n-undecylcyclohexyl) isothiocyanatobenzen (11CHBT) were established in the entire range of molar fraction by differential scanning calorimetry method, refractometry as well as density measurements. In this research the thermodynamic, optical, and volumetric properties of the eutectic mixture ( E 9 , 11 ) composed of 9CHBT and 11CHBT ( x 11 C H B T = 0.4 ) were studied and interpreted. The binary phase diagram is in comparable with that predicted from Schroder–van Laar equation. The excess functions were determined using the calculated activity coefficients of the eutectic mixture. Moreover, the temperature dependence of refractive indices, birefringence, and order parameters of the pure nematogens and the binary eutectic mixture was investigated. In contrast to the individual nematogens, the eutectic mixture ( E 9 , 11 ) displays a crossover temperature ( T CO ) based on the four-parameter model. Finally, results from quantum chemical calculations on the studied nematogens provide an overall supportive and coherent picture of the thermal, optical measurements. All calculations were performed using the Turbomole software package. The used methodology allows for an acceptable approximation of effective polarizabilities.