Mesomorphic Range Research Articles

Orientational Distribution Function and Order Parameters of Two 4′-Alkoxy-4-Cyanobiphenyls in Mesomorphic Phase

Abstract X-ray diffraction studies on samples of 4′-Pentyloxy-4-Cyanobiphenyl and 4′-Octyloxy-4-Cyanobiphenyl over the entire mesomorphic range are reported in this paper. A magnetic field was used to align samples. The orientational distribution functions f(β) have been calculated from the angular distribution of X-ray intensities. Orientational order parameters ( P 2) and ( P 4) have been calculated and compared with Maier-Saupe theoretical values. Expressions for the angular part of the pseudopotentials have been obtained from the temperature variation of f(β). The intermolecular distances D have been calculated from the experimental data and it is found that D is significantly smaller for well aligned samples. The apparent molecular length in the nematic phase and the layer thickness in the smectic phase have also been determined and are found to be about 1.4 times larger than the true molecular length in the fully extended form. This is in accordance with the findings from other cyano compounds.

Some Unusual Properties of 4-n-Decylphenyl-3′-Methyl-4′-(4″-Nitrobenzoyloxy)Benzoate

Abstract 4-n-Decylphenyl-3′-methyl-4′-(4″-nitro-benzoyloxy)benzoate (10 PMNBB) which exhibits the smectic A and nematic mesophases shows a large expansion (∼20%) of the bilayer spacing as it is cooled in the mesomorphic range. This is accompanied by a reversal in the sign of the dielectric anisotropy which becomes negative at lower temperatures.

Mesomorphic Characteristics of Thermotropic Mesogens p-p'-Disubstituted Phenyl Cinnamates 1: p-(p’ -n- Alkoxycinnamoyloxy)-Acetophenones

Abstract p-n-alkoxycinnamoyl cholrides when treated with p- hydroxyacetophenone yield a homologous series ofmesogens. The first member is a monotropic nematogen; exhibition of enantiotropic nematic mesophase begins from the second memeber and persists up to the butyl derivative. Both smectic and nematic mesophases are exhibited by the pentyl and hexyl derivatives. The homologues rom heptyl to octadecyl exhibit smectic phase only. the usual odd-even effect is well displyed. Nematic-isotropic treansition curves for both even and odd memebers showf an initial slight slump up to the heptyl derivative; the smectic-isotropic transition curve shows a rising tendency followed by a slight downward slope towards the highest member. The homologous series is thermally very stablef and exhibits a wide mesomorphic range. The thermal stabilities and other characteristics are discussed.

Schiffs Base Homologous Series of New Mesogens: p-(p′-n-Alkoxycinnamoyloxy) benzylidene-p″-N, N-Dimethylaminoanilines and p-(p′-n-Alkoxycinnamoyloxy) benzylidene-p″-N, N-Diethylaminoanilines

Abstract Two new homologous series comprising vinyl carboxy,—CH = CH—COO—, and azomethine,—CH = =N—, as central groups have been synthesized by treating p-(p'-n-alkoxycinnamoyloxy) benzaldehydes with p-amino N, N-dimethyl (I) and diethyl (II) anilines. All the twenty-four compounds are mesogenic in nature. Both series of liquid crystals are primarily nematogenic in character and high melting. Very wide range of mesomorphism is observed in all the homologues. In series (1) the first seven members decompose before passing into isotropic liquid form at higher temperatures because of which observation of the usual odd-even effect is missed. However, the series (II) homologues exhibit the usual odd-even effect since they do not decompose at higher temperatures. While the mesomorphic range is quite wide in series (I), that in series (II) is relatively less wide. The thermal stabilities are comparable. The special feature is that the smectic mesophase makes its appearance at very late stage; in series (I) at the...

Polymers with mesogenic elements and flexible spacers in the main chain: Aromatic‐aliphatic polyesters

AbstractA new series of aromatic‐aliphatic polyesters of general structure:magnified imageR1 = terphenyl, biphenyl, stilbeneR2 = (CH2)n;  CH2C(Me)2CH2;CH2;C(Et)2CH2; (CH2CH2O)n CH2CH2 has been synthesised. The existence of thermotrpic liquid crystalline phases has been shown by polarised light microscopy. The texture observations have suggested the existence of nematic, SA or/and SC phases depending on the chemical structure. The temperature of transition between the phases and, as a consequence, the range of mesomorphism are highly dependent upon the chemical structure. The clearing point is high, even for the longest aliphatic group, while the melting point is depressed.

Rigid backbone polymers. X. Transitions in bulk polyisocyanates

AbstractData obtained by hot‐stage cross‐polarized light microscopy and thermogravimetric analysis were used to plot a transition map for the poly(n‐alkylisocyanate) homologous family. Most members had a low‐temperature transition (or relaxation). The middle members of the family, with side‐chain length of 4 ≤ n < 13 carbon atoms, exhibit a mesomorphic range of temperatures. Members with sidechains of n ≥ 13 in length, go directly from the low‐temperature transition to the melting point without passage through a liquid crystalline state. A transition map for two homopolymers and a series of their copolymers, poly[x mol% n‐butyl + (100‐x)mol% p‐anisole‐3‐propyl]isocyanate, was also prepared. The range of mesomorphicity as a function of composition and temperature is clearly indicated.

Mesomorphic Properties of Bromo and Cyano Substituted Diarylethanes

Abstract Two homologous series of diarylethanes: 1-(4-alkoxy or alkyl-benzoyloxyphenyl)-2-(4′-bromo or cyanophenyl) ethanes (series I) and I-(4-alkoxy 3-bromo or cyanobenzoyloxyphenyl)-2-(4′-pentylphenyl) ethanes (series II) have been synthesized. The influence of the bromo or cyano group, in the meta or para position, on the mesomorphic range and the clearing point, is studied. In the series I, the bromo group induces a smectic polymorphism, whereas the cyano group induces nematic mesophases. In the series II, the larger the meta substituant, the lower the clearing point.

Synthesis and Mesomorphic Properties ofm-Cyano-orm-Halogeno-Benzoate Derivatives

Abstract Thirty four benzoate derivatives were prepared. They belong to the two following series: the 4-n-alkylphenyl 3-cyano-or 3-fluoro-4-n-alkoxybenzoates and the 4-n-alkylphenyl 4-(3-cyano-or 3-bromo-4-n-alkoxy-or 4-n-alkylbenzoyloxy-)benzoates. In the latter series all the compounds are measomorphic; in the former one, only 3-cyano compounds with long alkoxy chain, exhibit a small mesomorphic range. All the cya[ngrave]o compouns exhibit very high negative dielectric anisotropies.

Ultrasonic investigation of nematic liquid crystals in the isotropic and nematic phases

We report measurements of the frequency dispersion of ultrasonic attenuation for a nematic liquid crystal, the n-pentyl cyanobiphenyl in the vicinity of the nematic-isotropic transition. In the isotropic phase, the experimental results are well described by the theory recently proposed by Imura and Okano. The frequency ωmax at which the maximum of attenuation per wave length αλ occurs, as well as the peak value (α λ) max, diverge at the transition with the critical exponents predicted by the theory. We have extended the Imura-Okano theory to the nematic phase on the basis of a coupling between sinusoidal temperature variation induced by sound wave and the elastic Frank constants. This model accounts semi-quantitatively for the experimental results. We have also investigated the dependence of the low frequency attenuation with respect to the angle between the director and the acoustical wave-vector for a nematic liquid crystal (Merck V) which exhibits a broad mesomorphic range. Far below the transition temperature the experimental data are well described by the theory of Forster et al., provided that the frequencies are far below the intramolecular relaxational frequency.

The Effect on Thermal Nematic Stability of Schiff's Bases Upon Reversal of Terminal Substituents

Abstract Nematic liquid crystals have been found to produce dynamic light scattering when subjected to an electric field.(1) This electro-optic effect has stimulated widespread interest in the development of liquid crystals for display devices. It is desirable that the nematic material exhibit the nematic phase around ambient temperature and have a large mesomorphic range. No reported single component system meets these requirements although bis-(4′-n-octyloxybenzal)-2-chloro-1,4-phenylenediamine has a reported 120° nematic range just above ambient temperature (59–179°C).(2)