Refaat I. Nessim

Effect of molecular structure on the phase behaviour of some liquid crystalline compounds and their binary mixtures II. 4-Hexadecyloxyphenyl arylates and aryl 4-hexadecyloxy benzoates

4-Hexadecyloxyphenyl-4-substituted benzoates, Ia-d, and 4-substituted phenyl-4- hexadecyloxy benzoates, IIa-d, with the substituents CH3O, Cl, CN, and NO2, respectively, were prepared and characterized by infrared spectroscopy and the apparent solution dipole moment measured using cyclohexane as a solvent. Smectic A mesophase stability was investigated by differential scanning calorimetry and polarized light microscopy. The effects of structural changes on phase transitions in these two series of compounds are discussed in terms of dipole and mesomeric effects.

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 mixtures XIII. 4-(4-Substituted phenylazo)phenyl 4-alkoxybenzoates

Five homologous series of 4-(4-substituted phenylazo)phenyl 4-alkoxybenzoates (Ia–e) were prepared in which the substituent (X) was taken from CH3O, CH3, Cl, NO2, and CN, while, within each homologous series, the length of the terminal alkoxy group varied between 6 and 16 carbon atoms. Compounds prepared were characterized by infrared spectroscopy, and their mesophase behaviour investigated by differential scanning calorimetry and polarizing optical microscopy. The results are discussed in terms of mesomeric and polarizability effects. In each group of compounds bearing the same alkoxy group, the mesophase – isotropic transition temperatures (T c) were successfully correlated with the polarizability anisotropy of bonds to the substituent X.

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.

Effect of molecular structure on the phase behaviour of some liquid crystalline compounds and their binary mixtures VI[1]. The effect of molecular length

The apparent solution dipole moments of compounds based on 4,4-di-substituted phenyl benzoate (ROC6H4COOC6H4X), I, where X is a cyano group and R a terminal linear alkyl chain ranging from C12 to C20, were determined in cyclohexane at 30 C. The compounds were also thermally characterized by polarized light microscopy and differential scanning calorimetry. Phase diagrams were constructed for various binary mixtures prepared from any two homologues of series I as well as for every one of them with the nitro analogue II, where X is a nitro group and R C16H33. The study was undertaken in order to investigate the effect of the alkyl chain length on the mesophase behaviour. In order to assess the influence of structural variation in the central mesogenic group on the mesophase stability of pure and mixed compounds, the investigation was extended to cover binary mixtures of any two of the three compounds: analogue II (X=OC16H33), and the symmetric dialkoxy substituted phenyl esters (C16H33OC6H4COO)2 A, where A i...

Effect of steric factors on mesomorphic stability I. 4‐(4‐Substituted phenylazo)‐1‐naphthyl 4‐alkoxybenzoates

Four homologous series belonging to the family of 4‐(4‐substituted phenylazo)‐1‐naphthyl 4‐alkoxybenzoates (I a–d) (C n H2 n +1O–C6H4–COO–C10H6–N = N–C6H4–X) were prepared in which the 4‐ substituent (X) was varied between CH3O, CH3, Cl and NO2; while, within each homologous series, the number of carbon atoms, n, was varied between 8 and 14. The compounds were characterized by infrared spectroscopy, 1H NMR spectroscopy and elemental analysis. Their mesophase behaviour was investigated by differential scanning calorimetry and polarizing‐optical microscopy. The results are discussed in terms of mesomeric, polarizability, and steric effects. In each group of compounds bearing the same alkoxy group, attempts were made to correlate the mesophase–isotropic transition temperatures (T c) with the polarizability anisotropy, Δα x , of bonds to the small compact substituent X.

Effect of substituents and alkoxy-chain length on the phase behavior of 4-substituted phenyl-4-alkoxybenzoates

Abstract Four series of 4-substituted phenyl-4-alkoxybenzoates were prepared in which one substituent is a terminal alkoxy group with the number of carbon atoms kept constant (at n =6, 8, 14, or 16), while the other terminal substituent (X) alternatively changed from CH 3 O, CH 3 , Cl, CN, and NO 2 . Compounds prepared were characterized by infrared spectroscopy and their mesophase stabilities investigated by differential scanning calorimetry and polarized-light microscopy. The results were discussed in terms of mesomeric, polarity, and polarizability effects. In all four series, the mesophase–isotropic transition temperatures ( T c ) were successfully related to the polarizability anisotropy of bonds to the small compact substituent, X.

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 behaviour of binary mixtures of 4-substituted phenyl 4′-n-alkoxybenzoates

Five homologous series Ia-e, of the title compounds have been prepared and investigated for their mesophase behaviour in binary mixtures. Each series differs from the other by a substituent X, which changes between CH3O, CH3, Cl, CN, and NO2. The number of carbons in the terminal alkoxy group, within a homologous series, varies between 6, 8, 14, and 16. All possible binary combinations, made from any two components bearing an alkoxy group of the same chain length but two different substituents X, were prepared and similarly characterized for their phase behaviour. Transition temperatures of the mixtures were measured by differential scanning calorimetry and identified by polarizing optical microscopy. Phase diagrams were constructed for the various binary systems and discussed in terms of electronic effects.

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

Twentyfour liquid crystalline esters of the type 4-(n-C n H2n+1O)C6H4COOC6H4OOCC6H4-X-4 have been investigated for their phase behaviour. These compounds constitute six homologous series that differ from each other by the substituent X. The latter varies between CH3O, CH3, Cl, CN, NO2, and n-C n H2n+1O, and the number (n) of carbons varies, within a homologous series, between 6, 8, 14, and 16. All possible binary mixtures made from any two homologues were prepared and characterized for their mesophase behaviour by differential scanning calorimetry and polarizing optical microscopy.