The influence of polymer on optical and thermal properties of nematic liquid crystals

Polymer is substance which consists of large number of molecules and plays a very important in our everyday life. In the present study the effect of different concentration of polymer Poly Methyl Methacrylate on the optical and thermal properties of nematic liquid crystal were investigated. The polymer was dispersed in the liquid crystal by polymerization induced phase separation method. The physical properties were investigated using differential scanning calorimetry and polarized optical microscopy. We found various textures according to the molecular order and orientation of the liquid crystal and polymer in constrained regions separated by phase boundaries. These composite materials can be used to enhance contrast ratio with more stability for display application and smart window.

Synthesis, Characterization and Computational Study of Discotic Liquid Crystal Compounds

Discotic liquid crystal compounds were synthesized and characterized. Liquid crystalline texture of these compounds was investigated by polarized optical microscopy (POM). The Hartree-Fock approximation (HF) was used to calculate theoretical molecular parameters for synthesized compounds such as optimization, hardness, EHOMO, ELUMO, and energy gap using the Gaussian 09W program.

Thermal and Mesomorphic Investigations of 1:1 Supramolecular Assemblies of 4-[(4-(n-Alkoxy)phenylimino)methyl]benzoic Acids Having Symmetrical and Un-Symmetrical Terminal Chain Lengths

Thermal and mesomorphic properties of possible 1:1 supramolecular complexes (SMCs) (Im/In) designed from two members of 4-[(4-(n-alkoxy)phenylimino)methyl]benzoic acid with symmetrical or un-symmetrical alkoxy terminal flexible chains (carbons of m and n = 6, 8 and 16), were analyzed by differential scan-calorimetry (DSC), thermogravemetric (TG) analysis, and their mesophases identified by polarized optical microscopy (POM). The equimolecular mixtures of the two acids possess symmetrical and un-symmetrical terminal lengths. The mesomorphic properties of the binary mixtures were examined as a function of the total alkoxy chain length on both sides. Results revealed that the nematic mesophase temperature range increases as the total terminal length increases for all designed un-symmetrical mixtures. A comparison was constructed between the formed SMCs and of those of the previously prepared 4-n-alkoxyphenylazo benzoic acids as well as the 4-n-alkoxy benzoic acids, to examine the impact of mesogenic core on the mesomorphic properties. The comparison indicated that as the mesogenic portion lengthens the thermal mesophase stability exhibits higher values of phase transition temperatures; whereas, the azo and Schiff base moieties exhibited near thermal properties.

Effect of the Relative Positions of Di-Laterally Substituted Schiff Base Derivatives: Phase Transition and Computational Investigations

Two new laterally di-substituted derivatives namely, (E)-4-(((2-Chlorophenyl)imino)methyl)-3-methoxyphenyl 4-(alkoxy)benzoate, were designed and investigated for their mesomorphic properties. Elucidation of their molecular structures was carried out by elemental analyses, NMR and FT-IR, spectroscopy. Phase transitions were examined by differential scanning calorimetry (DSC) and polarized optical microscopy (POM). The optimized geometrical architectures of both compounds were deduced theoretically using GAUSSIAN 09 program. In order to establish the most probable conformation for each compound, four probable conformations were predicted for their positional isomers which vary according to the orientations of the two lateral groups. The results were used to correlate the experimental measurements with the predicted conformations. The study revealed that the investigated derivatives are non-mesomorphic and the orientations, as well as positions of the two-lateral groups, have a significant effect on the molecular packing of the molecules, their geometrical and thermal parameters.

2-{3,5-Bis-[5-(3,4-didodecyloxyphenyl)thien-2-yl]phenyl}-5-(3,4-didodecyloxyphenyl)thiophene

Star-shaped compounds are widely recognized as emerging materials for optical and electrical applications and as scaffolds of discotic liquid crystal. While the C3-symmetrical tri(phenylthienyl)benzene is the core for several electroopotical materials, no liquid crystal with this scaffold has yet been reported. Acid-catalyzed cyclocondensation of bromoacetylthiophene gives a C3-symmetrical star, threefold Suzuki coupling results in extension of the conjugated system. With 3,4-didodecylocyphenyl boronic acid, a star with a large rigid conjugated system and flexible aliphatic periphery is obtained. Differentials scanning calorimetry and polarized optical microscopy reveal an enantiotropic mesophase from 66 °C to 106 °C.

Synthesis, Thermal and Optical Characterizations of New Lateral Organic Systems

New laterally OCH3-substituted optical organic Schiff base/ester series, namely 4-(4-(hexyloxyphenyl)iminomethyl)-3-methoxyphenyl 4-alkoxybenzoates, were prepared and characterized with different thermal, mesomorphic, and photoactive techniques. The prepared group constitutes five homologues that differ from each other in the number of carbons in the terminal alkoxy chain (n), which varies between n = 6, 8, 10, 12, and 16 carbons. The laterally protruded methoxy group is attached to the central benzene ring that makes an angle of 120° with the molecular long axis. Molecular structures of all newly prepared homologues were fully elucidated via FT-IR, 1H and 13C NMR spectroscopy. Mesomorphic transitions were determined via differential scanning calorimetry (DSC) and the phases identified by polarized optical microscopy (POM). Independent of the length of the terminal alkoxy chain attached to phenyl ester ring, only a monomorphic nematic (N) phase was observed for all the synthesized compounds. A comparative study was made between the present lateral methoxy-substituted homologues and their corresponding laterally-neat analogues. The results revealed that, depending on the length of the alkoxy chain and the presence or absence of the lateral methoxy group, different mesophases with different thermal stability and temperature ranges were observed. Finally, UV-vis spectra showed that the present nematogenic series possess photoactive properties that are of importance for many applications.

A chiral–racemic lyotropic chromonic liquid crystal system

A lyotropic chromonic liquid crystal consists of oriented molecular assemblies in solution. If the molecules are chiral, the helical pattern of orientational order is revealed by the stripes seen with polarized optical microscopy.

Impact of Substitution Pattern and Chain Length on the Thermotropic Properties of Alkoxy-Substituted Triphenyl-Tristriazolotriazines

Tristriazolotriazines (TTTs) with a threefold alkoxyphenyl substitution were prepared and studied by DSC, polarized optical microscopy (POM) and X-ray scattering. Six pentyloxy chains are sufficient to induce liquid-crystalline behavior in these star-shaped compounds. Thermotropic properties of TTTs with varying substitution patterns and a periphery of linear chains of different lengths, branching in the chain and swallow-tails, are compared. Generally, these disks display broad and stable thermotropic mesophases, with the tangential TTT being superior to the radial isomer. The structure–property relationships of the number of alkyl chains, their position, length and structure were studied.