Schroder Van Laar Research Articles

Optical and thermodynamic studies on binary mixtures composed of two-isothiocyanato liquid crystals

Phase diagram and optical properties of the nematic mixtures containing two-isothiocyanatobenzen liquid crystal (7CHBT and 9CHBT) were studied by refractometry and DSC measurements. The thermodynamic and optical properties of the eutectic mixture (E79) composed of 7CHBT and 9CHBT were identified and studied. The phase diagram of the eutectic system was compared with the Schroder–van Laar calculation. The excess thermodynamic properties of the eutectic mixture were calculated and interpreted in terms of intermolecular interactions. The modified four-parameter model was used to fit the temperature dependence of the nematogen parameters on the refractive index. In addition, the temperature gradient of the ordinary refractive index (dno/dT) of the nematogens was analyzed in a convenient framework. The order parameters and polarizabilities of the nematic compounds, which are important parameters, were calculated through different methods based on birefringence measurements. Finally, the eutectic mixture and one of the constituent component (7CHBT) display crossover temperatures (TCO), which is very important liquid crystal parameter for specific applications such as optical devices and nonlinear optics.

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

• 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.

Binary phase diagrams of pyridinecarboxamide isomers

Pyridinecarboxamide binary phase diagrams have been established using differential scanning calorimetry, infrared spectroscopy and X-ray powder diffraction. Simulated diagrams obtained using with the Schroder-van Laar and Prigogine–Defay equations are in very good agreement with experimental data. The binary systems nicotinamide (Form I)–picolinamide (Form II) and isonicotinamide (Form II)—picolinamide (Form I and Form II) occur as eutectic mixtures. Nicotinamide (Form I)—isonicotinamide (Forms II and Form I) solid–liquid phase diagram confirms formation of the cocrystal with molar ratio of 1:1, whose crystal structure was already solved by Bathori et al. (Cryst Growth Des 11:75–87, 12) with X-ray diffraction on single crystals obtained by crystallization from common solution of nicotinamide and isonicotinamide. The corresponding eutectic composition and temperatures, beyond polymorphism of isonicotinamide and picolinamide under these molecular environments are discussed.

Measurement and correlation of solid–liquid equilibria for three binaries, ethanol–antipyrine, chloroform–antipyrine, and dimethyl ether–antipyrine

Solid–liquid equilibrium (SLE) was measured for three binaries systems, ethanol–antipyrine, chloroform–antipyrine, and dimethyl ether–antipyrine by use of two apparatus based on a direct temperature measuring method. For dimethyl ether–antipyrine, a high pressure variable volume cell was employed, and the pressure was held constant at 5 MPa. Other measurements were carried out by use of a pressure resistance glass tube at the bubble point pressure. Prior to the measurements, SLE was measured for cyclohexane–naphthalene to ensure the reliability of the method. Comparing the three binary systems containing antipyrine, the molar solubility of antipyrine in chloroform was 1.5 times larger than that in ethanol, and 13.5 times larger than that in dimethyl ether at 313 K. The data were correlated with Schroder-van Laar and NRTL equations under the assumption that the binary system had a simple eutectic temperature. The data could be correlated within 0.168%, 0.775%, and 0.102% in temperature for the ethanol–antipyrine, chloroform–antipyrine, and dimethyl ether–antipyrine binary systems, respectively.

A new approach to study interaction parameters in cyanobiphenyl liquid crystal binary systems

The phase transition of heptylcyanobiphenyl 7CB and pentylcyanobiphenyl 5CB liquid crystals was investigated using the differential scanning calorimetry DSC technique. Then, the phase transition of different compositions of 7CB/5CB binary mixture was studied to determine the eutectic point. The phase diagram of mentioned binary system in 7CB mole fraction of 0.45 at T=273.45K is in good agreement with that of predicted from Schroder–van Laar equation. The thermodynamic excess functions and interaction parameters were calculated to describe the phase transition physically using the non-random mixing for the first time. The P∗ randomicity parameter was used to describe the phase transitions of C–N and N–I in which a small amount of P∗ shows a non-random identity of C–N phase transition. Contrarily, the P∗ is greater in N–I phase transition showing a random mixing process.

Separation and Solubility of Cis and Trans Isomers in Nanostructured Double-Decker Silsequioxanes

A fractional crystallization method was used to separate the cis and trans isomers of three double-decker silsesquioxanes (DDSQs) with an aminophenyl moiety in a THF + hexanes solvent mixture. The experimental solubilities were fitted to the Schroder–van Laar equation with activity coefficients determined using the NRTL model by adjusting the binary interaction parameters. The ability to separate these cis and trans isomers was affected by the regioisomer (m- or p-aminophenyl) and the R moiety (cyclohexyl or methyl) coupled via silicon. For a given DDSQ compound, the variances between the solubilities of the cis and trans isomers depend on differences in thermal properties (Schroder–van Laar). Cis isomers were 33 times more soluble than trans isomers for p-aminophenyl (R = methyl) and 22 times more soluble for the analogous m-aminophenyl in a solution of THF and hexanes. For a more sterically hindered m-aminophenyl (R = cyclohexyl), the cis isomers were only 3.5 times more soluble, and the overall solubil...

Solid state structural relation and binary melting phase diagram of (S-) and racemic 2-(2-nitro-1-phenylethyl)-1,3-diphenyl-propane-1,3-dione

Abstract Both the S enantiomer and the racemic (RS) forms of 2-(2-nitro-1-phenylethyl)-1,3-diphenyl-propane-1,3-dione (1) have been obtained from the same reaction media by fractional crystallization from toluene. First, the racemic compound, (R,S)-1, was precipitated (mp. 159.7 °C), then, from the filtrate, (S)-1 (mp. 135.6 °C) was crystallized. The absolute configuration (S) and crystal structure of (S)-1 has been solved by single crystal X-ray diffraction (R = 0.0377). (S)-1 crystallizes in the orthorhombic crystal system (space group P212121 (19), a = 10.6377(2) A, b = 11.4348(2) A, c = 31.3543(6) A, Z = 8, Z′ = 2). Powder XRD pattern of the racemic crystal (R,S)-1 could be indexed in the orthorhombic space group Pbca (61) (a = 22.18(7) A, b = 17.08(3) A, c = 9.96(3) A, Z = 8, Z′ = 1). Differences in secondary bonding interactions and crystal stability of both (S)-1 and (R,S)-1 were evaluated on the basis of their FTIR spectra, melting points, and enthalpies of fusion. The expected eutectic-type binary melting phase diagram of (S)-1 and (R,S)-1 crystals has been constructed based on differential scanning calorimetric (DSC) measurements and calculation of the liquidus curves according to the combination of the simplified Schroder–van Laar and Prigogine–Defay equations.

Binary Phase Studies of 4-4'-N-Pentylcyanobiphenyl

The phase behavior for three binary liquid crystalline systems has been explored. All three contained the room-temperature nematic, 4-4'-n-pentylcyanobiphenyl (K15), as one of their components. K15 has a T KN of 22.3 o C and a T NI of 35.1 o C. The second component for each system is a member of the homologous series 4-[4-alkylcyclohexyl]cyanophenyl. The n-ethyl (S1236), n-butyl (S1188) and n-heptyl (S1115) members of this series were chosen. The eutectic composition of all three systems was found to occur at ≃60 mole % K15. The nematic range of the eutectic composition for the S1236/K15, S1188/K15 and the S1115/K15 system is 16, 27 and >40 o C, respectively. The Schroder-van Laar (S-vL) equation was found to be useful in predicting the eutectic composition for each binary system. The K15/S1236 phase diagram shows a new phase between 10 and 62 mole % K15. This phase is believed to be a co-smectic

New Methods for Calculating the Temperatures and the Enthalpy Changes of Virtual Transitions and Predicting Phase Diagrams-Applied to the Tolans

Abstract For a mesogen which does not exhibit an enantiotropic nematic phase when pure, two new methods are proposed for the determination of the temperatures and enthalpy changes of the nematic-isotropic liquid virtual transitions. These calculations, based on Schroder-van Laar and van Laar equations, use the value of the liquid appearance temperature (the determination of which is easy and accurate) for mixtures of the compound with another mesogen which exhibits the enantiotropic mesophase when pure. Both methods are applied to the study of the first ten compounds in the series: 4-methoxy-4′-n-alkyl-tolan. The results are then used to determine the eutectic, liquid appearance and nematic disappearance temperatures of mixtures of two tolans that do not exhibit an enantiotropic nematic phase when pure. In seven cases, an enantio-tropic nematic phase is predicted and observed; in one case, the phase diagram differs from that expected; for the remainder, there is a good agreement between calculated and exp...

Determination de la purete des substances chimiques par analyse calorimetrique differentielle (A. C. D.)

Purity determination by DSC is possible if the impurity concentration lies within the limits 0.01 to 20 mole%. The thermodynamic equation of Schroder-Van Laar was used.