Mesogenic Groups Research Articles

Synthesis and Properties of an N-Substituted Polypyrrole with Liquid Crystalline Moieties

The synthesis and characterisation of two pyrrole monomers substituted at the N-position with a liquid crystal group are reported. Polymerisation of one of these compounds produced a soluble liquid crystalline semiconducting polymer. The side-chain of the polymer had a flexible spacer of nine methylene units, terminated by a mesogenic cyanobiphenyl group. The new compounds were chemically characterised and were found by hot-stage polarised optical microscopy to exhibit liquid crystal mesophases. The polymer was lightly doped p-type by exposure to iodine vapour, and its electrical conductivity was measured. The polymer synthesis and doping/dedoping processes were also briefly studied by cyclic voltammetry.

The influence of a magnetic field on the morphology and thermomechanical properties of a liquid crystalline epoxy carbon composite

The synthesis of a novel ordered liquid crystalline epoxy carbon composite was presented in this article. Anthracite thermally modified at 2,000°C (SV2000) having graphitic structure was used as a filler in the composite with matrix obtained by crosslinking a liquid crystalline diepoxy monomer LCEM containing triaromatic mesogenic group. The curing agent was 4,4′‐diaminodiphenylmethane. The morphology and thermomechanical properties of the final products were characterized by differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), and wide angle X‐ray scattering (WAXS) analysis. It was found by WAXS measurements that alignment of LCEM was effectively induced in the matrix and in the composite filled with SV2000 by applying external magnetic field during cure. Thermosets with locked smectic C structure were obtained in all cases, with mesogenic fragments arranged along the applied field. The experimental results indicated that the presence of SV2000 as the filler of composite partially decreased the degree of order. The oriented composites exhibited anisotropy of the dynamic‐mechanical properties. POLYM. COMPOS., 39:E2573–E2583, 2018. © 2018 Society of Plastics Engineers

Thermal stability and structural anisotropy of semiaromatic poly(ester amides) from aromatic bis(2-oxazolines) and aliphatic dicarboxylic acids

Semiaromatic poly(ester amides) containing three different aromatic units and aliphatic spacers with five different chain lengths were investigated using various experimental methods, with a focus on the effect of structural changes in the mesogenic groups and the length of the flexible alkylene spacer on the observed physical properties. The results of thermal stabilities and crystallographic measurements indicate that the thermal stability is dependent on the content of the amorphous phase in the polymer. The results from the thermal stability, differential scanning calorimetry (DSC), wide-angle X-ray diffraction (WAXD), and optical microscopy of the poly(ester amides) containing aromatic moieties were compared to the dielectric properties recorded using dielectric relaxation spectroscopy (DRS). DRS contributed to the description of four relaxation regions detected by matching the temperature and frequency dependencies of the dielectric functions. For the poly(ester amides) containing biphenyl units, the presence of a liquid-crystalline (LC) phase was observed.

Floating liquid crystalline molecularly imprinted polymer coated carbon nanotubes for levofloxacin delivery

Liquid crystalline molecularly imprinted polymers (LC-MIPs) were low cross-linking MIPs (5–20 mol%) by introducing a LC monomer into the MIP polymerization system to keep the shape of the imprinted cavities due to additional interactions between the mesogenic groups. The multiwalled carbon nanotubes (MWCNTs) coated LC-MIP (MWCNT@LC-MIP) was the first fabricated as a novel floating interaction-controlled DDS. The synthesis was achieved by adding 9-vinylanthracene to obtain the high-density vinyl group functionalized MWCNTs firstly, and then polymerization of LC MIPs was performed on the surface of MWCNTs using a mixture of methacrylic acid, ethylene glycol dimethacrylate, and 4-methyl phenyl dicyclohexyl ethylene (LC monomer) with levofloxacin (LVF) as model template drug. Both template/functional monomer ratio and levels of crosslinker were optimized to obtain the best imprinting factor. Characterizations of polymer were investigated by the transmission electron microscope, nitrogen adsorption, thermogravimetric analysis, Fourier transform infrared spectra and floating behavior studies. The imprinting effect was confirmed by the adsorption isotherms, adsorption kinetics and effect of selectivity. In vitro release studies were examined by the LVF-loaded MWCNT@LC-MIP and the control samples, MWCNT@LC-NIP, MWCNT@MIP, MWCNT@NIP and the bare MWCNT using acetonitrile as the dissolute medium. The release profiles showed an obvious zero-order release of LVF from MWCNT@LC-MIP, which exhibited 3.8 μg/h of the release rate with duration of about 20 h. In vivo pharmacokinetic study displayed the relative bioavailability of the gastro-floating MWCNT@LC-MIP was 578.9%, whereas only 58.0% of MWCNT@MIP and 11.7% of the bared MWCNT. As a conclusion, MWCNT@LC-MIP showed potentials for oral administration by the innovative combination of floating and controlled release properties.

Analysis of High Thermal Conductivity Mechanism of 2,7-Naphthalene Benzoate Twin Mesogen Epoxy Polymer That Have Alkyl Chain Length 4

ABSTRACTWe synthesized twin-mesogen epoxy polymer in which there were two 2,7-naphthalene benzoate as mesogens connected by four carbons alkyl chain and investigated the effects of higher-order structure changes due to the differences of alkyl chain length and mesogen groups on thermal conductivities. This polymer is abbreviated as TME2,7-NB4. NB means naphthalene benzoate and 4 means spacing carbon number. As a result, the thermal conductivity of TME2,7-NB4 was higher than that of TME2,7-NB8, but the coherent length D was less than that of TME2,7-NB8.

“Cool-off” Function and Heat Resistance of an Acrylic Pressure Sensitive Adhesive Bearing a Mesogenic Group

We have prepared an acrylic pressure sensitive adhesive bearing a mesogenic group (MesP) as a thermosensitive unit and heat resistance one. MesP showed a cool-off function, where MesP loses its adhesion below the glass transition temperature and gives enough adhesion above that. Remarkably, peel modes of MesP at 250 °C and 20 °C after heating at 250 °C were adhesive failure that means interfacial failure between the PSA and adherent whereas those of an acrylic pressure sensitive adhesive bearing a long-alkyl side-chain group (C22P) were cohesive failure (CF) and a mixture of CF and stick-slip, respectively.

Synthesis and comparison of mesomorphic behaviour of a cholesterol-based liquid crystal dimer and analogous monomers

ABSTRACTOligo/polymerisation of known mesogens constitutes a highly efficient strategy in liquid crystal research due to its potential to generate novel liquid crystal materials with intriguing mesomorphic properties. Here we report the synthesis and comparative studies of a synthetic liquid crystal dimer and two of its monomer analogues. By incorporating cholesterol as the mesogenic group, we designed a flexible scaffold consisting of a hybrid of non-polar hydrophobic chain and polar tetraethylene glycol appended to the cholesteryl mesogens. Detailed studies showed that the two classes of mesogens exhibit the same type of liquid crystal phases with similar dimensions but their transition temperatures varied which can be effectively rationalised by the particular chemical functionalities present in each class of materials.

Molecular organizations of conical mesogenic fullerenes.

We have studied liquid crystal phases formed by fullerenes functionalized with mesogenic groups yielding a cone-shaped molecular structure. We have modelled these shuttlecock-like molecules with a set of Gay-Berne particles grafted with flexible springs to a spherical core and we have studied, using Monte Carlo simulations, their phase organization, also with a view to examining their possible use as candidate organic photovoltaic materials. We have found that, upon cooling from the isotropic phase, the system forms a columnar phase, like in the experimental work of Kato and coworkers [T. Kato et al., Nature, 2002, 419, 702]. However the phase is made of polar stacks extending not more than about ten molecules, which could limit their usefulness in enhancing and directing charge transport for possible photovoltaic applications.

Thermal and mechanical properties of tetra‐functional mesogenic type epoxy resin cured with aromatic amine

ABSTRACTA novel tetra‐functional epoxy monomer with mesogenic groups was synthesized and characterized by 1H‐NMR and FTIR. The synthesized epoxy monomer was cured with aromatic amine to improve the thermal property of epoxy/amine cured system. The glass transition temperature (Tg) and coefficient of thermal expansion (CTE) of the cured system were investigated by dynamic mechanical analysis and thermal mechanical analysis. The properties of the cured system were compared with the conventional bisphenol‐A type epoxy and mesogenic type epoxy system. The storage modulus of the tetra‐functional mesogenic epoxy cured systems showed the value of 0.96 GPa at 250 °C, and Tg‐less behavior was clearly observed. The cured system also showed a low CTE at temperatures above 150 °C without incorporation of inorganic components. These phenomena were achieved by suppression of the thermal motion of network chains by introduction of both mesogenic groups and branched structure to increase the cross linking density. The temperature dependency of the tensile property and thermal conductivity of the cured system was also investigated. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 46181.

Organic gels prepared from side‐chain liquid crystalline polymers without the spacer

A series of side‐chain liquid crystal polymers (SCLCPs) without the spacer, named poly[ω‐(4′‐n‐alkyl oxybiphenyl‐4‐oxy)methacrylate (PMBiCm, m = 1, 2, 4, 6, 8, 10, 12, 14, 16, and 18), have been synthesized. The novel polymer organogels were prepared by introducing PMBiCm into common organic solvents. Solubility and gel properties of polymer organogelators differ widely according to the nature of the solvents. In aromatic solvents, PMBiCm completely dissolved in solvent due to good compatibility between biphenyl mesogen group and aromatic solvents. Poly[ω‐(4′‐n‐alkyl oxybiphenyl‐4‐oxy)methacrylate were still insoluble in polar solvents such as acetone, ethanol, DMF, ethylene glycol, and n‐butanol. This behavior resulted from mismatch of solubility parameter between PMBiCm and solvent. Considering the factors of solvent, we have systematically studied 3 organic solvents with different polarities (butyl acetate, n‐butyl amine, and n‐heptane). It is found that the length of the alkoxy tail chain of the SCLCPs has significant influence on gelability and gel thermal stability. In further studies discussed by UV‐Vis spectroscopy, the results revealed that the π‐π stacking interaction of the biphenyl mesogens might be the key factor for guiding the self‐assembly processes and the polymer gel formation. This work is useful to comprehending physical mechanism of polymer organogels. Meanwhile, those expand SCLCPs to a wide range of applications.

New chiral liquid crystal materials based on menthol: Synthesis and phase behavior

ABSTRACTTo study structure-mesomorphism relationships of chiral materials based on menthol, a series of chiral compounds containing menthyl group were synthesized. Their chemical structures, formula, and the purity were characterized by Fourier transform infrared (FTIR), proton nuclear magnetic resonance (1H NMR), and elemental analyses. The corresponding phase behavior was investigated with differential scanning calorimetry (DSC) and polarizing optical microscopy (POM). The effect of the mesogenic core, flexible spacer, and terminal groups on the mesophase formation and type was discussed. The compound 4-menthyloxyacetoxybenzoyloxy-4′- (6-bromohexyloxy)biphenyl showed the smectic A (SA) and cholesteric phases on heating cycle, and a cubic Blue Phase, chiral smectic C (SC*), SA and cholesteric phases on cooling cycle. However, the compound 4-menthyloxyacetoxybenzoyloxy-4′-(4-bromobutoxy)biphenyl showed enantiotropic SC*, SA and cholesteric phases, moreover, the platelet texture of a cubic Blue Phase was also observed on cooling cycle. The methacrylate monomer with six flexible methylene units and three phenyl rings as mesogenic core only showed cholesteric phase, while the methacrylate monomer with four methylene unit and three phenyl rings showed the SC* and cholesteric phases. However, when the terminal methacryloyloxy groups in the monomers were substituted by thiophenylacryloyloxy groups, the corresponding monomers all show no mesophase. With increasing the rigidity of mesogenic core or decreasing the flexible methylene spacer length, the corresponding melting temperature (Tm) or isotropic temperature (Ti) increased.

Hunting for smectic C in calamitic azobenzene ionic liquid crystals with different cationic head groups

AbstractThe tilted smectic C phase is a rather uncommon phase in ionic liquid crystals (ILCs), whereas the orthogonal smectic A phase is the most common phase in ILCs. We now present 2 new groups of mesogens with an azobenzene core that exhibit smectic C as well as smectic A phases. Their phase sequences and tilt angles were studied by polarizing microscopy, and their temperature‐dependent layer spacings and orientational order parameters were investigated by X‐ray diffraction. We present 1 new amidinium azobenzene mesogen that forms enantiotropic smectic C and A phases and another amidinium as well as 2 new guanidinium azobenzene mesogens that exhibit monotropic smectic C and enantiotropic smectic A phases. With this study, we show that azobenzene is indeed an SmC‐promoting group in ILCs. Comparing these results with our earlier results on azobenzenes with an N‐methylimidazolium head group (N Kapernaum et al, ChemPhysChem 2016, 17, 4116‐4123), we show that the aromaticity of the imidazolium head group plays an important role in the formation of smectic C phases.

Synthesis of novel and regioselectively mesogen-incorporated thermotropic liquid crystals from cellulose derivatives

ABSTRACTRegioselectively mesogen-incorporated cellulose derivatives, in which the hydroxy group at C-6 is displaced by a bulky and rigid mesogenic group such as {4-[(4-methoxyphenoxy)carbonyl]phenoxy}acetate or [(4′-cyanobiphenyl-4-yl)oxy]acetate, and the C-2 and C-3 groups are displaced by octanoyl or lauroyl groups, were synthesized. Thermogravimetric and differential scanning calorimetric analyses of the final products, along with polarized optical microscopic observations, revealed that the obtained cellulose derivatives have a thermotropic liquid-crystalline nature and transition from the mesomorphic to the isotropic phase over a wide range of temperatures. These derivatives could be considered to be main-chain liquid-crystalline cellulosic polymers.

Unusual electro-optical behaviour of the nematic polyacrylate

ABSTRACTHigh sensitivity of liquid crystals to the electric field makes them highly demanded and widely used in different applications. Despite the large number of the electro-optical research on the low-molar-mass liquid crystals electro-optics of the liquid crystalline (LC) polymers is much less studied. Herein, the comparative electro-optical behaviour of two nematic comb-shaped polyacrylates with phenylbenzoate mesogenic side groups was studied in detail. These two polyacrylates have completely the same structure of polymer backbone and spacer length but different in the direction of the ester group in the phenylbenzoate fragments. It was found that this difference predetermines their completely opposite electro-optical properties.The influence of the electric field of different strength and frequency on the orientation of the mesogenic groups of these polymers is studied. It is shown that application of the electric field at temperatures above the glass transition temperature (~25°C) induces reorientation of the mesogenic groups along or perpendicular to the electric field direction depending in its turn on the ester group direction. For one of the polyacrylates an unusual textural transition is found; during cooling of the polymer sample under applied field at definite temperature a sharp change in the mesogen’s orientation from homeotropic to planar one is found. This electro-optical phenomenon is observed for the first time and probably associated with sharp change in sign of anisotropy of dielectric permittivity from positive (at high temperatures) to negative one (at lower temperatures). Kinetics of the electro-optical switching at different temperatures, influence of the molar masses of the polymer and frequency of the applied AC field on electro-optical behaviour of the polymers are studied. The possibility of the fixation of the electroinduced homeotropic alignment of the mesogenic groups by photopolymerisation of the diacrylate dissolved in the polymer is demonstrated.

English

Two novel azo phenols mesogenic group namely 2-sec-butyl-4-(p-tolyldiazenyl)phenyl 4-(dodecyloxy) benzoate I12a,and 4-((4-bromophenyl)diazenyl)-2-sec-butylphenyl 4-(dodecyloxy) benzoate I12b were synthesized .The prepared compound were characterized using FT-IR, 1H-NMR, Mass Spectroscopy and Elemental Analysis. Their mesophase was investigated by Differential Scanning Calorimetry (DSC). Their antioxidant efficiency for Egyptian lubricating base oil was tested via monitoring the oxidation reaction through the change in total acid number (TAN) and viscosity. The obtained results showed that, the efficiency of these compounds was ranked as follows I12a > I12b.

Influence of alkylene spacer length on photoinduced orientation of liquid crystalline polymer with N-benzylideneaniline side groups

ABSTRACTLiquid crystalline polymers (LCPs) comprised of N-benzylideneaniline (NBA) side groups with different alkylene spacer length (n = 2, 6, and 10) are synthesized and their photoinduced reorientation behavior is investigated. Photoinduced orientation of NBA side groups is observed for all LCP films when exposing to LP-365 nm light, but the out-of-plane motion is simultaneously generated. When the polarization of LP-365 nm light is changed, in-plane optical anisotropy is reversibly changed and the out-of-plane motion is restricted for a P1 (n = 2) film. In contrast, reversibility of the photoinduced in-plane orientation is not effective for P2 (n = 6) and P3 (n = 10) films, where out-of-plane motion of the mesogenic NBA side groups is generated when the total exposure energy increases.

PA30 メソゲン基を有する直鎖状ポリウレタンの熱的性質と秩序化(化学・材料,ポスター発表,2013年日本液晶学会討論会)

PA30 メソゲン基を有する直鎖状ポリウレタンの熱的性質と秩序化(化学・材料,ポスター発表,2013年日本液晶学会討論会)

PBal9 光架橋性高分子液晶フィルムの光・熱誘起配向における側鎖末端基の影響

PBal9 光架橋性高分子液晶フィルムの光・熱誘起配向における側鎖末端基の影響

PA63 側鎖にフェニルベンゾエート・メソゲンを有するポリメチレンの液晶構造解析(ソフトマター,ポスター発表,2015年日本液晶学会討論会)

PA63 側鎖にフェニルベンゾエート・メソゲンを有するポリメチレンの液晶構造解析(ソフトマター,ポスター発表,2015年日本液晶学会討論会)

Liquid crystalline polyaniline and phthalocyanine-based polysiloxanes bearing lateral fluoro-substituted benzoic acid groups

ABSTRACTA series of novel liquid crystalline polymers (PI, PII, PIII and PIV) containing lateral fluoro-substituted benzoic acid groups was synthesised using cholesteryl 4-(2-propenyloxy)-benzoate, 4-(allyloxy)-3-fluorobenzoic acid and poly(methylhydrogeno)siloxane. PI and PII showed smectic phase, but PIII and PIV showed chiral nematic phase due to more lateral fluoro-substituted benzoic acid groups in the polymer systems. Liquid crystalline polyaniline (PAN) and phthalocyanine (Pc)-based polysiloxanes showing chiral nematic phase were prepared by use of Pc, PAN and these liquid-crystalline polymers via hydrogen bond. PAN-based polysiloxanes showed different liquid crystalline behaviours from Pc-based polysiloxanes due to the difference of molecular structure. PAN-based polysiloxanes showed greater d-spacings between the side mesogenic groups than Pc-based polysiloxanes due to long rod-like geometrical shapes. Hydrogen bond based on lateral fluoro-substituted benzoic acid groups was formed to different geometrical shapes (strip or roundness) between PAN and Pc-based polysiloxanes.