Effect of molecular structure on the phase behaviour of some liquid crystalline compounds and their mixtures VIII. Quaternary mixtures of enantiotropes

Transition temperatures of quaternary mixtures prepared from the cyano and nitro derivatives of the two series, 4-hexadecyloxyphenyl 4-substituted benzoates (Ia,b) and 4-substituted phenyl 4-hexadecyloxy benzoates (IIa,b) have been determined by DSC and the transitions identified with polarized light microscopy. The cyano and nitro derivatives, in both series, were used because their molecules are enantiotropic. The method described before for the ternary system was extended to elucidate the eutectic composition of the quaternary system from the knowledge of either the eutectic compositions of the four possible ternary mixtures or of those of the six individual binary systems. A general equation was deduced to calculate the eutectic composition of any multi-component system from values determined for their individual binary systems. T_c values of binary, ternary, or quaternary mixtures were related to the polarizability anisotropy, Deltaalpha_X, of the individual C_Ar-X bonds. The mixture law was successfully applied.     

Effect of molecular structure on the phase behaviour of some liquid crystalline compounds and their mixtures IX. Multi-mixtures of a monotrope and enantiotropes

Transition temperatures of the ternary and quaternary mixtures, prepared from the enantiotropic cyano and nitro derivatives of the two series, 4-hexadecyloxyphenyl 4-substituted benzoates (Ia,b) and 4-substituted phenyl-4'-hexadecyloxy benzoates (IIa,b) with the monotropic methoxy derivative (IIc), have been determined by DSC and identified with polarized light microscopy. The equation deduced to calculate the eutectic composition of a multicomponent system from values determined for their individual binary systems, was found to be fairly applicable to our non-ideal systems. Conversely, values of clearing temperatures (T_c), calculated from the polarizability anisotropy (Δα_X) of the individual C_Ar-X bonds, are often less than those measured, indicating complex formation between the methoxy and nitro derivatives.     

Effect of molecular structure on the phase behaviour of some liquid crystalline compounds and their mixtures VII. Ternary mixtures of enantiotropes

Transition temperatures of the ternary mixtures, prepared from compounds of the two series, 4-hexadecyloxyphenyl 4-substituted benzoates (Ia,b) and 4-substituted phenyl 4-hexadecyloxy benzoates (IIa,b) have been determined by differential scanning calorimetry and identified with polarized light microscopy. The cyano and nitro derivatives, in both series, were used because their molecules form enantiotropic phases. A new method was elaborated for the elucidation of the eutectic composition of any ternary system from the knowledge of the eutectic composition of the three individual binary mixtures.     

Effect of molecular structure on the phase behaviour of some liquid crystalline compounds and their mixtures VII. Ternary mixtures of enantiotropes

Transition temperatures of the ternary mixtures, prepared from compounds of the two series, 4-hexadecyloxyphenyl 4-substituted benzoates (Ia,b) and 4-substituted phenyl 4-hexadecyloxy benzoates (IIa,b) have been determined by differential scanning calorimetry and identified with polarized light microscopy. The cyano and nitro derivatives, in both series, were used because their molecules form enantiotropic phases. A new method was elaborated for the elucidation of the eutectic composition of any ternary system from the knowledge of the eutectic composition of the three individual binary mixtures.     

Mesophase stability in binary mixtures of monotropic nematogens

Binary phase diagrams were constructed from laterally substituted methyl azo/ester derivatives, namely 4-(4″-substituted phenylazo)-3-methyl phenyl-4″-alkoxy benzoates (In_a–d). In this group of compound the unsubstituted and chloro-substituted derivatives possess the nematic phase monotropically, while the nitro and methyl analogues are enantiotropically nematogenic. The binary phase diagrams constructed were made once from the monotropic nematogens with each other, and another with the enantiotropic nematogens. In both the cases enantiotropic nematic phase was observed that covers a wide range of composition. The mesophase behaviour of all binary mixtures was investigated by differential scanning calorimetry (DSC) and polarised light microscopy (PLM). The nematic phase was exhibited in all binary mixtures. Independent of the alkoxy chain length, the entropy change, ΔS_N–I of the N–I transition of pure components was found to vary irregularly with the anisotropy of polarisability (?α_X) of the polar substituent, X.     

Effect of molecular structure on the phase behaviour of some liquid crystalline compounds and their binary mixtures IV. Dependence of Tc on the anisotropy of the aryl-X of polarizability bond

Transition temperatures of binary mixtures of the two series, 4-hexadecyloxyphenyl-4- substituted benzoates (Ia-d) and 4-substituted phenyl-4-hexadecyloxybenzoates (IIa-d), have been determined on cooling and the phase diagrams compared with those previously obtained on heating. Tc values for the monotropes and the non-LC analogues have been evaluated by extrapolation. Examination of both series revealed that the square root of Tc is related to the polarizability anisotropy, Delta alphaX , of the CAr-X bond, except for the methoxy derivatives.     

Effect of molecular structure on the phase behaviour of some liquid crystalline compounds and their binary mixtures III. Binary mixtures of alkoxyphenyl arylates and arylalkoxybenzoates

4-Substituted phenyl-4-hexadecyloxybenzoates and 4-hexadecyloxyphenyl-4-substituted benzoates were prepared and thermally characterized by differential scanning calorimetry. Transition temperatures were identified by polarized-light microscopy. Substituents were chosen to cover a wide range of electronic and dipolar characteristics. Binary mixtures of different components were prepared and similarly characterized to construct their phase diagrams. In mixtures of the 4-CN and 4-NO2 analogues, enhanced SmA mesophases were found when either of these esters was mixed with one of the methoxy analogues. A weak molecular complex is proposed to account for this non-ideal solution behaviour. Linear or slightly enhanced mixture behaviours were found for the nitro or cyano derivatives when mixed with each other. The results are interpreted in terms of electronic, dipolar, and molecular interactions.     

New room temperature nematogens by cyano tail termination of alkoxy and alkylcyanobiphenyls and their anchoring behavior on metal salt-decorated surface

ABSTRACT

A series of cyano tail-terminated alkoxy and alkyl cyanobiphenyl compounds and some cyano-p-terphenyl derivatives were synthesized and mesogenic properties described. Comparison with the K series and M series indicates that the terminal cyano group generally enhances the supercooling of the molecules. Furthermore, several binary LC mixtures formed by the cyano tail-terminated compounds were found exhibiting promising room temperature nematic phases ranges comparable to the commercial quaternary mixture E7. The equimolar binary mixture of CN5OCB and CN7OCB shows homeotropic ordering at the metal salts-decorated surfaces and planar ordering at the free surface, which is consistent with G_BE values we calculated. As such, these materials are promising candidates for sensor devices which display a rapid response to a variety of analytes.     

Effect of orientation of lateral methyl substituent on the thermal behaviour of the mesophase in binary systems of 4-substituted phenyl 4ʹ-(4”-alkoxy phenylazo) benzoates

Several binary systems made from two laterally substituted azo/ester isomers, namely 2?- (and 3?-) methyl-4-substituted phenyl 4?-(4?-alkoxyphenylazo) benzoates, where the length of the terminal alkoxy group = 8 and 16 carbons, while the other terminal substituent, X, varies between CH₃O, CH₃, H, Br and CN groups, were investigated using differential scanning calorimetry (DSC) and phases identified by polarised light microscope (PLM). For the sake of comparison, two another binary systems made from 2?- (or 3?-) methyl-4-substituted phenyl 4?-(4?-alkoxyphenylazo) benzoates (n = 8 and X = CH₃) each was mixed with its laterally neat analogue and similarly investigated. Results were discussed on the basis of constructed phase diagrams whereby various mesomorphic properties were observed dependent on X, n, and position of the lateral methyl group. In most of the cases, the mixtures exhibited eutectic compositions, while linear or nearly linear nematic and smectic A-composition temperature dependence were observed.     

Study of the NaF-NaBr-NaVO3 system and its boundary elements

By differential thermal analysis, the NaBr-NaVO₃ binary system and the NaF-NaBr-NaVO₃ ternary system were studied, the melting points and compositions of eutectic mixtures were determined, and in-, mono-, and divariant equilibrium states were described.     

Influence of lateral methyl and terminal substituents on the mesophase behaviour of four rings azo-ester liquid crystal compounds

ABSTRACT

The effect of introducing a lateral methyl substitution into the previously investigated laterally neat four-ring analogues, 4-substituted phenylazo phenyl 4?-(4?-alkoxyphenylazo) benzoates (In_a–e), on their mesophase behaviour was investigated for the newly prepared five homologous series of 4-substituted phenylazo phenyl 4?-(3?-methyl-4?-alkoxyphenylazo) benzoates (IIn_a–e). Within each homologous series, the alkoxy group varies between 6, 8, 10, 12, 14, and 16 carbons, while the substituent, X, is a polar group that alternatively changes between the electron-donating (CH₃O and CH₃) groups, and the electron-withdrawing (Br and NO₂) groups, including the unsubstituted homologues (IIn_c). Their mesophase stabilities were determined by DSC and phases identified by PLM. The results showed that independent of the alkoxy-chain length or the polarity of the substituent X, the nematic phase is predominant with relatively high stability and wide temperature ranges. All compounds show a good thermal stability in the mesophases domain, except the nitro and Br substituted derivatives bearing short alkoxy chain length. Comparison of the mesophase behaviour was also made between the present series and corresponding three-ring laterally CH_3-substituted azo/ester analogues. UV-vis absorption spectra revealed that derivatives with electron donating or an electron withdrawing groups exhibited redshifts of the π→π* transition compared with unsubstituded derivative.     

Effect of lateral bromo substituent on the phase behavior of four-ring azo/ester/azo liquid crystalline materials

ABSTRACT

In order to study the influence of lateral Br substitution on mesophase behaviour, five homologous series of 4-substituted phenylazo phenyl 4?-(3?-bromo-4?-alkoxyphenylazo) benzoates (In_a–e) have been synthesised. Within each homologous series, the alkoxy group varies from 6 to 16 carbons, while other terminal group substituents, X, are CH₃O, CH₃, H, Br and NO₂ groups; the mesophase behaviour of these series is compared with previously prepared laterally neat analogues, 4-substituted phenylazo phenyl 4?-(4?-alkoxyphenylazo) benzoates (IIn_a–e) and laterally methyl analogues, 4-substituted phenylazo phenyl 4?-(3?-methyl-4?-alkoxyphenylazo) benzoates (IIIn_a–e). Similar to lateral methyl analogues, the present series, lateral Br substitution showed that, independent of the polarity of the substituent X or the alkoxy-chain length, the nematic phase is predominant with relatively high stability and broad temperature ranges. The mesophase stability varies between 204.0°C and 335.0°C for the nematic phase and 169.6°C and 281.0°C for the SmA phase. Their total mesophase temperature ranges vary between 87.2°C and 201.4°C. All compounds were found to be thermally stable within the mesophase temperature range, except the lower homologue of the nitro and Br substituted derivatives. The obtained results are discussed in terms of molecular polarisability.     

Topological investigations of binary and ternary mixtures: excess isentropic compressibilities

The speed of sound, U_ij 1,3-dioxolane (D) in binary mixtures (ij) with benzene, cyclohexane, n-hexane or n-heptane and U_ijk for 1,3-dioxolane in ternary mixtures (ijk) with the same hydrocarbons have been measured as a function of composition at 298.15 K. The observed data have been utilised to evaluate excess isentropic compressibility of binary, (κ_s^E)_ij and ternary (κ_s^E)_ijk mixtures using density and speed of sound values of the binary and ternary mixtures. The Moelyn-Huggins concept of interaction between the molecular surfaces of the components of a binary mixture [Polymer 12 (1971) 389] has been extended to evaluate excess isentropic compressibility of the studied binary and ternary mixtures. It has been observed that κ_s^E values predicted by a graph-theoretical approach using connectivities of third degree for binary mixtures compare reasonably well with their corresponding experimental values and κ_s^E for ternary mixtures are of the same sign and order of magnitude.     

Effect of molecular structure on the phase behaviour of some liquid crystalline compounds and their mixtures XI. Binary mixtures of unsymmetrical 1,4-phenylene bis-(4-substituted benzoates)

Binary mixtures formed from components of the four series of unsymmetrical 1,4-phenylene bis-4-substituted benzoates, in which one substituent is a terminal alkoxy group with a number of carbon atoms kept constant (at n =6, 8, 14 and 16) while the other substituent (X) ranges through CH₃O, CH₃, Cl, CN and NO₂, were prepared and characterized for their mesophase behaviour. Transition temperatures of the mixtures prepared were measured by differential scanning calorimetry and identified by polarizing optical microscopy. Phase diagrams for the various binary combinations were constructed to investigate the dependence of the phase behaviour of mixed systems upon the electronic nature of the terminal group X, as well as on the chain length of the alkoxy group. The results are discussed in terms of mesomeric and polarizability effects.     

Phase diagrams and physical properties of binary ferroelectric mixtures based on a series of chiral α-cyanocinnamate derivatives

We report a detailed investigation of binary mixtures composed of members of the homologous series of (S)-4′-(2-n-alkoxypropanoyloxy)biphenyl-4-yl 4-n-alkoxy- f-cyanocinnamates. The phase transition curves for these mixtures have no minima. On the contrary, eutectic behaviour was obtained if the members of this homologous series were mixed with structurally different chiral cinnamic acid derivatives and other ferroelectric liquid crystal materials. Spontaneous polarization, tilt angle and dielectric constant results were obtained for three of the single compounds and nine ferroelectric mixtures.     

Experimental and predicted excess molar volumes of the ternary system.

Summary Experimental excess molar volumes for the ternary system x₁MTBE+x₂1-propanol+(1-x₁-x₂) heptane and the three involved binary mixtures have been determined at 298.15 K and atmospheric pressure. Excess molar volumes were determined from the densities of the pure liquids and mixtures, using a DMA 4500 Anton Paar densimeter. The ternary mixture shows maximum values around the binary mixture MTBE+heptane and minimum values for the mixture MTBE+propanol. The ternary contribution to the excess molar volume is negative, with the exception of a range located around the rich compositions of 1-propanol. Several empirical equations predicting ternary mixture properties from experimental binary mixtures have been applied.     

Interaction in the manganese sulfate-carbamide-sulfuric acid-water system at 25°C

Heterogeneous equilibria in the manganese-carbamide-sulfuric acid-water quaternary system at 25°C are studied using the solubility method. The concentration boundaries are determined for crystallization of the initial solid components, eutectic compositions of the ternary systems, and binary compounds formed in the carbamide-sulfuric acid-water and carbamide-manganese sulfate-water systems, as well as for new compounds simultaneously containing carbamide, manganese sulfate, and sulfuric acid at a 1: 4: 1 and 1: 2: 1 ratios.     

Experimental excess molar volumes of the ternary mixture and comparisonwith several empirical methods

Experimental excess molar volumes for the ternary system {x₁MTBE+x₂1-propanol+(1–x₁–x₂)nonane} and the three involved binary mixtures have been determined at 298.15 K and atmospheric pressure. Excess molar volumes were determined from the densities of the pure liquids and mixtures, using a DMA 4500 Anton Paar densimeter. The ternary mixture shows maximum values around the binary mixture MTBE+nonane and minimum values for the mixture MTBE+propanol. The ternary contribution to the excess molar volume is negative, with the exception of a range located around the rich compositions of 1-propanol. Several empirical equations predicting ternary mixture properties from experimental binary mixtures have been applied.     

Solubility of selected dibasic carboxylic acids in water,in ionic liquid of [Bmim][BF4], and in aqueous [Bmim][BF4] solutions

The solubilities of three dibasic carboxylic acids (adipic acid, glutaric acid, and succinic acid) in water, in the ionic liquid of 1-butyl-3-methyl-imidazolim tetrafluoroborate ([Bmim][BF₄]), and in the aqueous [Bmim][BF₄] solutions have been measured by a solid-disapperance method. The binodal curve of water + [Bmim][BF₄] was also determined experimentally from solid–liquid–liquid coexistence temperature up to near the upper critical solution temperature. Experimental results showed that each acid-containing binary behaved as a simple eutectic system. The solid–liquid equilibrium (SLE) data were correlated with the NRTL model for each binary system. The NRTL model with these determined binary parameters predicted the solid-disappearance temperatures of the aqueous ternary mixtures containing [Bmim][BF₄] and the dibasic acids to within an average absolute deviation of 2.0%.