Thermotropic Liquid Crystalline Behavior Research Articles

Influence of the length of end-group double bond substituents on the temperature change of phase transition in liquid crystals

ABSTRACT A series of nematic liquid crystal (LC) monomers, containing a reactive group in the lateral substituent, were designed and synthesised through an organic synthesis reaction. Considerable changes were made to the properties of the liquid monomers by varying the terminal alkyl chain lengths. The molecular structures of the intermediates and the LC monomers were characterised by flourier infrared absorption spectrometry and proton nuclear magnetic resonance (1H NMR) spectroscopy, leading to the identification of the target product. The phase transition temperatures of the LC monomers were observed and analysed using differential scanning calorimetry (DSC) and polarising optical microscopy (POM) with a hot stage. The two-way thermotropic liquid crystalline behaviour was observed during the heating process, providing insight into the effect of substituent changes on the phase transition temperature.

Non-covalent planarizing interactions yield highly ordered and thermotropic liquid crystalline conjugated polymers.

Controlling the multi-level assembly and morphological properties of conjugated polymers through structural manipulation has contributed significantly to the advancement of organic electronics. In this work, a redox active conjugated polymer, TPT-TT, composed of alternating 1,4-(2-thienyl)-2,5-dialkoxyphenylene (TPT) and thienothiophene (TT) units is reported with non-covalent intramolecular S⋯O and S⋯H-C interactions that induce controlled main-chain planarity and solid-state order. As confirmed by density functional theory (DFT) calculations, these intramolecular interactions influence the main chain conformation, promoting backbone planarization, while still allowing dihedral rotations at higher kinetic energies (higher temperature), and give rise to temperature-dependent aggregation properties. Thermotropic liquid crystalline (LC) behavior is confirmed by cross-polarized optical microscopy (CPOM) and closely correlated with multiple thermal transitions observed by differential scanning calorimetry (DSC). This LC behavior allows us to develop and utilize a thermal annealing treatment that results in thin films with notable long-range order, as shown by grazing-incidence X-ray diffraction (GIXD). Specifically, we identified a first LC phase, ranging from 218 °C to 107 °C, as a nematic phase featuring preferential face-on π-π stacking and edge-on lamellar stacking exhibiting a large extent of disorder and broad orientation distribution. A second LC phase is observed from 107 °C to 48 °C, as a smectic A phase featuring sharp, highly ordered out-of-plane lamellar stacking features and sharp tilted backbone stacking peaks, while the structure of a third LC phase with a transition at 48 °C remains unclear, but resembles that of the solid state at ambient temperature. Furthermore, the significance of thermal annealing is evident in the ∼3-fold enhancement of the electrical conductivity of ferric tosylate-doped annealed films reaching 55 S cm-1. More importantly, thermally annealed TPT-TT films exhibit both a narrow distribution of charge-carrier mobilities (1.4 ± 0.1) × 10-2 cm2 V-1 s-1 along with a remarkable device yield of 100% in an organic field-effect transistor (OFET) configuration. This molecular design approach to obtain highly ordered conjugated polymers in the solid state affords a deeper understanding of how intramolecular interactions and repeat-unit symmetry impact liquid crystallinity, solution aggregation, solution to solid-state transformation, solid-state morphology, and ultimately device applications.

Crystal and mesophase structure of a bicyclohexyl cyano mesogen.

The phase behaviour of 4-[trans-4-(trans-4-propylcyclohexyl)cyclohexyl]benzonitrile, C22H31N, 1, has been examined. This compound has two different solid phases, denoted I and II, and exhibits thermotropic liquid-crystalline behaviour, with a remarkable interval of stability of the mesophase between the lower melting solid phase (75 °C) and the isotropization temperature (247 °C). The crystal and molecular structures of solid phase I have been determined at 173 K. The cyclohexyl rings both adopt the chair conformation and are equatorially substituted. The packing of 1 in the crystalline state is driven by the antiparallel arrangement of cyano dipoles with the formation of close contacts involving the strong cyano acceptor and weak aromatic C-H or aliphatic C-H donors. The crystal packing is discussed and compared with X-ray diffraction data in the liquid-crystalline state. The combination of thermal analysis, optical polarizing microscopy and X-ray diffraction analysis suggests that the mesophase is a partially ordered smectic phase. The lamellar structure of the mesophase is retained in crystalline solid phase II obtained by cooling the liquid-crystalline phase.

Lyotropic Liquid-Crystalline Phases of Sophorolipid Biosurfactants.

Biological amphiphiles derived from natural resources are presently being investigated in the hope that they will someday replace current synthetic surfactants, which are known pollutants of soils and water resources. Sophorolipids constitute one of the main classes of glycosylated biosurfactants that have attracted interest because they are synthesized by non-pathogenic yeasts from glucose and vegetable oils at high titers. In this work, the self-assembly properties of several sophorolipids in water at high concentrations (20-80 wt %), a range so far mostly uncharted, have been investigated by polarized-light microscopy and X-ray scattering. Some of these compounds were found to show lyotropic liquid-crystalline behavior as they display lamellar or hexagonal columnar mesophases. X-ray scattering data shows that the structure of the lamellar phase is almost fully interdigitated, which is likely due to the packing difference between the bulky hydrophilic tails and the more compact aliphatic chains. A tentative representation of the molecular organization of the columnar phase is also given. Moreover, some of these compounds display thermotropic liquid-crystalline behavior, either pure or in aqueous mixtures. In addition, small domains of the lamellar phase can easily be aligned by applying onto them a moderate a.c. electric field, which is a rather unusual feature for lyotropic liquid crystals. Altogether, our work explored the self-assembly liquid-crystalline behavior of sophorolipids at high concentration, which could shed light on the conditions of their potential industrial applications as well as on their biological function.

Regioregularity-Dependent Crystalline Structures and Thermal Transitions in Poly(3-dodecylthiophene)s

The liquid crystalline (LC) characteristics of conjugated polymers (CPs) can result in their self-assembly with long-range ordering, providing an effective route for the formation of an optimized morphology suitable for high-performance organic electronic devices. In this study, the temperature-dependent LC phases of regioregularity (RR)-controlled poly(3-dodecylthiophene)s (P3DDTs) are systematically investigated. Controlling the RR of P3DDTs from 94 to 60% significantly modifies the strengths of their LC interactions, whereas their chemical structures remain almost the same. As the RR decreases, P3DDTs exhibit progressively decreased phase transition temperatures, i.e., the nematic-to-isotropic transition temperature, as measured using polarized optical microscopy (POM), UV–vis spectroscopy, differential scanning calorimetry (DSC), and X-ray scattering. P3DDTs with a high RR (94 and 83%) exhibit only the Form I crystal structures that are typically observed in most regioregular poly(3-alkylthiophene)s. However, P3DDTs with a low RR (76 and 60%) adopt both the Form I and Form II crystal structures, where Form II crystals contain interdigitated alkyl side-chain stackings. The amount of Form I crystals is significantly decreased as the RR decreases, and Form II crystals are dominantly observed for RR 60% P3DDT polymers. These features explain the significant decreases in the transition temperatures between the phases for P3DDTs with lower RR. This study provides an understanding of the RR effect in determining the crystalline structures and thermotropic LC behavior of P3DDTs, allowing for exquisite control over their self-assembly and optoelectrical properties.

Ion conformation and orientational order in a dicationic ionic liquid crystal studied by solid-state nuclear magnetic resonance spectroscopy

Ionic liquids crystals belong to a special class of ionic liquids that exhibit thermotropic liquid-crystalline behavior. Recently, dicationic ionic liquid crystals have been reported with a cation containing two single-charged ions covalently linked by a spacer. In ionic liquid crystals, electrostatic and hydrogen bonding interactions in ionic sublayer and van der Waals interaction in hydrophobic domains are the main forces contributing to the mesophase stabilization and determining the molecular orientational order and conformation. How these properties in dicationic materials are compared to those in conventional monocationic analogs? We address this question using a combination of advanced NMR methods and DFT analysis. Dicationic salt 3,3′-(1,6-hexanediyl)bis(1-dodecylimidazolium)dibromide was studied. Local bond order parameters of flexible alkyl side chains, linker chain, and alignment of rigid polar groups were analyzed. The dynamic spacer effectively “decouples” the motion of two ionic moieties. Hence, local order and alignment in dicationic mesophase were similar to those in analogous single-chain monocationic salts. Bond order parameters in the side chains in the dicationic smectic phase were found consistently lower compared to double-chain monocationic analogs, suggesting decreasing contribution of van der Waals forces. Overall dication reorientation in the smectic phase was characterized by low values of orientational order parameter S. With increased interaction energy in the polar domain the layered structure is stabilized despite less ordered dications. The results emphasized the trends in the orientational order in ionic liquid crystals and contributed to a better understanding of interparticle interactions driving smectic assembly in this and analogous ionic mesogens.

Water Solubility and Surface Activity of Alkoxyethyl β-d-Maltosides.

Green surfactants alkyl glycosides are key to solve the inherent problem of water solubility due to their commercial application and extensive scientific research. Based on the enhancement strategy of hydrophilicity through the reconstruction of the conventional alkyl β-d-maltoside by introducing an oxyethyl group (-OCH2CH2-), d-maltose was used to prepare a series of nonionic disaccharide-based surfactants alkoxyethyl β-d-maltosides (4a-h, n = 6-16) so that the related water solubility was effectively improved, while the corresponding surface activity and other excellent properties were still maintained. Their physicochemical properties, including water solubility, surface activity, moisture absorption, and thermotropic liquid crystalline behavior, were investigated. The liquid crystal texture of alkoxyethyl β-d-maltosides (n = 7-16) has a fan-shaped focal conic texture. Furthermore, decoxyethyl β-d-maltoside had the strongest foaming characteristic and the best foam stability. Moreover, dodecoxyethyl β-d-maltoside (4f, n =12) had stronger emulsifying activity in the rapeseed oil/water system. Finally, CTAC/4f binary surfactants had an obvious synergistic effect. Such β-d-maltosides should have good application prospects in the future.

Mesomorphic Sugar‐Coated Polydiacetylene Polymers

AbstractThe derivatization of a polydiacetylene (PDA) polymer with free hydroxyl groups containing sugars leads to amphiphilicity of the polymer and the emergence of thermotropic liquid crystalline behavior, in addition to the thermochromatic properties. The diacetylene monomers, incorporated with mono‐ and disaccharides, exhibit mono‐ and/or enantiotropic phase behavior in a wide temperature range. Structural characterization and modeling studies reveal a lamellar arrangement and interdigitization of the molecules in the mesophase. The importance of the amphiphilicity as a source to induce mesomorphic behavior in PDA polymers is emphasized.

Paramagnetic iron-containing ionic liquid crystals

Iron-containing ionic liquid crystals of N,N′-dialkylimidazolium salts ([(CnH2n+1)2IM]3[Fe(CN)6], with n = 12 (1), 14 (2), 16 (3), 18 (4), IM = imidazolium) were prepared and their structures and properties were characterized. Differential scanning calorimetry (DSC), polarizing optical microscopy (POM) as well as powder X-ray diffraction (PXRD) analysis reveal for all compounds thermotropic liquid crystalline behavior. The observed textures point to smectic A and smectic X phases. The crystal structure of the solvate [C12C12IM]3[Fe(CN)6]·2 DMSO (DMSO = dimethylsulfoxide) was examined by single crystal X-ray diffraction analysis which reveals two crystallographically independent [C12C12IM]+ cations with different conformation, U-shape and rod-shape, together with a nearly ideal octahedral [Fe(CN)6]3− anion and two DMSO solvent molecules. The crystal packing is characterized by alternating bilayers of almost linearly arranged imidazolium cations with the U-shaped cations being arranged in a head-to-head fashion and the cations' hydrophobic dodecyl chains being interdigitated. Magnetic measurements for compounds 1–4 show paramagnetic moments, μeff, of ~1.7 μB, which are close to the theoretically expected value for a d5 low-spin Fe3+ spin-only S = 1/2 system (μeffs.o. = 1.73 μB). It was possible to obtain an Fe3+ containing ILC material that combines liquid crystalline behavior over a large mesophase window (from 33 °C to 170 °C) with high magnetic susceptibility by mixing compound 3 with [C16C16IM][FeCl4] (5), which contains the d5 high-spin Fe3+ ion (S = 5/2). All compounds are highly hydrophobic and stable in the atmosphere indicating a great potential of applications as functional materials.

Design of Ionic Liquid Crystals Forming Normal-Type Bicontinuous Cubic Phases with a 3D Continuous Ion Conductive Pathway

We have prepared a series of pyridinium-based gemini amphiphiles. They exhibit thermotropic liquid–crystalline behavior depending on their alkyl chain lengths and anion species. By adjusting the alkyl chain lengths and selecting suitable anions, we have obtained an ionic amphiphile that exhibits a normal-type bicontinuous cubic phase from 38 °C to 12 °C on cooling from an isotropic phase. In the bicontinuous cubic liquid–crystalline assembly, the pyridinium-based ionic parts align along a gyroid minimal surface forming a 3D continuous ionic domain while their ionophobic alkyl chains form 3D branched nanochannel networks. This ionic compound can form homogeneous mixtures with a lithium salt and the resultant mixtures keep the ability to form normal-type bicontinuous cubic phases. Ion conduction measurements have been performed for the mixtures on cooling. It has been revealed that the formation of the 3D branched ionophobic nanochannels does not disturb the ion conduction behavior in the ionic domain while it results in the conversion of the state of the mixtures from fluidic liquids to quasi-solids, namely highly viscous liquid crystals. Although the ionic conductivity of the mixtures is in the order of 10–7 S cm–1 at 40 °C, which is far lower than the values for practical use, the present material design has a potential to pave the way for developing advanced solid electrolytes consisting of two task-specific nanosegregated domains: One is an ionic liquid nano-domain with a 3D continuity for high ionic conductivity and the other is ionophobic nanochannel network domains for high mechanical strength.

Effects of Lateral and Terminal Chains of X-Shaped Bolapolyphiles with Oligo(phenylene ethynylene) Cores on Self-Assembly Behavior. Part 2: Domain Formation by Self-Assembly in Lipid Bilayer Membranes.

Supramolecular self-assembly of membrane constituents within a phospholipid bilayer creates complex functional platforms in biological cells that operate in intracellular signaling, trafficking and membrane remodeling. Synthetic polyphilic compounds of macromolecular or small size can be incorporated into artificial phospholipid bilayers. Featuring three or four moieties of different philicities, they reach beyond ordinary amphiphilicity and open up avenues to new functions and interaction concepts. Here, we have incorporated a series of X-shaped bolapolyphiles into DPPC (1,2-dipalmitoyl-sn-glycero-3-phosphocholine) bilayers of giant unilamellar vesicles. The bolapolyphiles consist of a rod-like oligo(phenylene ethynylene) (OPE) core, hydrophilic glycerol-based headgroups with or without oligo(ethylene oxide) expansions at both ends and two lateral alkyl chains attached near the center of the OPE core. In the absence of DPPC and water, the compounds showed thermotropic liquid-crystalline behavior with a transition between polyphilic and amphiphilic assembly (see part 1 in this issue). In DPPC membranes, various trends in the domain morphologies were observed upon structure variations, which entailed branched alkyl chains of various sizes, alkyl chain semiperfluorination and size expansion of the headgroups. Observed effects on domain morphology are interpreted in the context of the bulk behavior (part 1) and of a model that was previously developed based on spectroscopic and physicochemical data.

Thermotropic liquid crystalline polyesters derived from 2-chloro hydroquinone

Synthesis of thermotropic liquid crystalline polyesters derived from bis[4-hydroxy benzoyloxy]-2-chloro-1,4-benzene (BHBOCB) and aliphatic dicarboxylic acid chlorides by interfacial polycondensation methodology is presented. Synthesised polyesters consist of bis[4-hydroxy benzoyloxy]-2-chloro-1,4-benzene as a mesogen and aliphatic diacid chloride as flexible spacer. The length of oligomethylene units in the polymer was varied from the trimethylene to the dodecamethylene groups. Synthesized polyesters were characterized by differential scanning calorimetry and optical microscopy. The transition temperatures and thermodynamic properties were studied for all these polymers. These polyesters exhibited thermotropic liquid crystalline behavior and showed nematic texture except decamethylene spacer. Decamethylene spacer based polyester showed marble texture of smectic C. Mesophase stability of these polyesters was higher than $$123{^{\circ }}\hbox {C}$$ (except first heating cycle of PE-1). SYNOPSIS The present study deals with the synthesis of thermotropic liquid crystalline polyesters derived from bis[4-hydroxy benzoyloxy]-2-chloro-1,4-benzene (BHBOCB) and aliphatic dicarboxylic acid chlorides by interfacial polycondensation methodology.

Liquid crystalline supramolecular crosslinked polymer complexes of ditopic rylenebisimides and P4VP

ABSTRACTPerylenebisimide and naphthalenebisimide (PBI‐PDP and NBI‐PDP) end functionalized with pentadecyl phenol is designed as ditopic hydrogen bonding acceptors to form supramolecular crosslinked network with poly(4‐vinyl pyridine) (P4VP). The pristine PBI‐PDP has been grown as single crystals from DCM‐MeOH (dichloromethane‐methanol) mixture at room temperature, which revealed a P21 space group. Noticeably, the pentadecyl alkyl chain shields the aromatic perylene core on both sides resulting in the absence of π–π interaction in single‐crystal assembly. The naphthalenebisimide derivative exhibits thermotropic liquid crystalline behavior, while both the molecules exhibits lyotropic liquid crystalline phases in tetrahydrofuran (THF), which were characterized using a combination of differential scanning calorimeter, X‐ray diffraction, and polarized light microscopy. The hydrogen‐bonded complex of both the rylenebisimides with P4VP preserves the mesomorphic properties in THF. The electron transport mobility measured by space charge limited current measurements reveals a two orders of magnitude increase in the charge transport in the P4VP complex compared to that of the pristine molecule. The average electron mobility obtained is μe,avg: 10−3 cm2/Vs for P4VP‐PBI compared to μe,avg: 10−5 cm2/Vs for pristine PBI derivative. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017, 55, 951–959

Lyotropic liquid crystalline phthalocyanines containing 4-((S)-3,7-dimethyloctyloxy)phenoxy moieties

The novel metal free phthalocyanine and its copper complex which are octa-substituted at the peripheral positions with 4-(([Formula: see text]-3,7-dimethlyoctyloxy)phenoxy moieties were synthesized and characterized by FT-IR, 1H NMR and mass spectroscopy. Their mesomorphic properties were studied by polarizing optical microscopy. The spectroscopic properties and aggregation behaviors of the novel phthalocyanines were also investigated by UV-vis spectroscopy in different solvents with same concentration as well as in a wide range of concentrations of chloroform. Both compounds with chloroform and [Formula: see text]-dodecane clearly show the lyotropic columnar mesophase in a wide temperature range whereas thermotropic liquid crystalline behavior for both compounds is not observed. Both of these novel compounds show no aggregation in toluene, tetrahydrofuran, dichloromethane and chloroform.

Synthesis and phase transitions of monomers carrying a biphenyleneazobenzene or an azotolane group. Precursors of photo-responsive liquid crystal polymers

Four functional methacrylate monomers, two of them carrying a biphenyleneazobenzene group, and the other two an azotolane group, were synthesized. The synthetic route involved several reactions, among which are the Suzuki-Miyaura and Sonogashira cross-coupling reactions that allowed us to prepare long rigid rodlike azobenzene cores. The chemical structure of these new azo-monomers was confirmed by proton nuclear magnetic resonance (1H NMR) spectroscopy, and the thermotropic liquid-crystalline behavior was determined from differential scanning calorimetry (DSC), polarizing optical microscopy (POM) and X-ray diffraction (XRD) analyses. The four monomers showed a mesomorphic behavior that extends over a broad temperature range. The phase transitions of the monomers carrying a biphenyleneazobenzene core were much broader and weaker than those of monomers carrying an azotolane group. Also, the former showed no crystallization in cooling to room temperature. The four studied monomers displayed liquid crystal phases with lamellar order (SmA and SmC), but only those carrying an azotolane core developed an additional nematic phase. The lamellar stacking of monomers is discussed in terms of lateral interactions between the rigid rodlike cores. Both types of monomers showed a trans to cis photo-conversion of around 90% when irradiated with UV–light. These new monomers are precursors of photo-responsive liquid crystal polymers.

Mesomorphism and molecular flexibility in novel chalconyl derivatives with two phenyl rings

ABSTRACTA novel chalconyl liquid crystalline (LC) homologous series with two phenyl rings and one central bridge RO−C6H4−CH=CH–CO−C6H4(O−C18H37) (meta) has been synthesized and studied with a view to understanding and establishing the effects of molecular structure on thermotropic LC behaviors or properties. Homologous series of present investigation (C1–C18) consists of thirteen homologues, and thermotropic mesomorphism for nematic and smectic commences from C3 and C6 homologues respectively. The C3, C4, and C5 homologues are enantiotropically nematic, whereas, the homologues from C6 to C18 are monotropically smectic plus nematic. Melting points and transition temperatures were determined using a polarizing optical microscope (POM) equipped with a heating stage. The textures of the nematic phase are threaded or Schlieren and that of a smectic phase are fan shaped of smectic-A or smectic-C type. The Cr−I/M, N−I/I−N, and N-Sm transition curves behave in the normal manner, and the Cr-I/M exhibits an odd-even effect. Analytical, thermal, and spectral data confirm the molecular structures. Thermal stabilities of smectic and nematic are low. Mesophase lengths are very short, ranging between 1–8°C and 14°C. The novel compounds are compared with a known series.

Designer Peptide Dendrons and Dendrimers Based Soft Materials Through Self‐Assembly

AbstractA series of new aspartic and glutamic acid based peptide dendrons and dendrimers were designed and synthesized. The supramolecular assembly of these novel molecules were studied by scanning electron microscopy (SEM), atomic force microscopy (AFM), and attenuated total reflectance Fourier transform infrared (ATR‐FTIR) spectroscopy. The dendrons and dendrimers formed gel in aqueous or in organic phase with excellent storage modulus as measured by rheometry. Glutamic acid‐based higher generation dendrons and dendrimers showed a minimum gelation concentration as low as 1 wt/v (%) in CHCl3. Interestingly, the higher generation dendrimers 5 d, 6 d, and 7 d gelated even polar solvent DMSO. The lipidated peptide dendrons showed thermotropic liquid crystalline behavior with the formation of columnar and smectic phase as confirmed by differential scanning calorimetry (DSC) and polarization optical microscopy (POM). These lipidated peptides exhibited well‐ordered specific modes of self‐assembly and hence could be exploited for several applications such as drug delivery vehicles and in tissue engineering.

Mesomorphism dependence on halogenated chalconyl esters in terms of molecular flexibility/rigidity

ABSTRACTVinyl carboxy central group containing a novel chalconyl ester homologous series: RO.C6H4.CH ˭ CH.COO.C6H4.CH ˭ CH.CO.C6H4.I (para) have been synthesized and studied with a view to understand and establish the relation between thermotropic liquid crystalline (LC) behaviors and the molecular structure. Novel chalconyl ester homologous series consists of thirteen homologs (C1–C18). C1–C3 homologs are nonmesogenic, C4 homolog is enantiotropic nematogenic and the rest of the homologs (C5–C18) are enantiotropically smectogenic plus nematogenic. Phase transition temperatures and textures of LC phase were determined by an optical polarizing microscopy (POM) equipped with a heating stage. Cr-M/I, Sm-N, N-I transition curves in a phase diagram behaved in normal manner. Sm-N and N-I transition curves exhibited odd-even effect from C4–C10 or nearby C10 homolog. Textures of nematic phase are threaded or Schlieren and that of the smectic phase are of the type smectic A or C. Analytical and spectral data confirms the molecular structure of homologs. Thermal stabilities for smectic and nematic mesophases are 155.0 and 180.7, respectively, and their corresponding mesophaselengths are varied from minimum to maximum at 17.0°C–39.0°C as well as 15.0°C–30.0°C. Thus, it is middle ordered melting type series. The group efficiency orders derived on the basis of smectic and nematic thermal stabilities are as under: Sm: -C6H4.I > -C6H4.Cl > -C4H3S and N:- C6H4.I > -C6H4.Cl > -C4H3S from comparative study of structurally similar analogous series

Unsymmetrically substituted room temperature discotic liquid crystals based on hexa–peri–hexabenzocoronene core

AbstractThe first discotic system based‐on alkoxy (tri‐ & di‐) substituted hexa‐peri‐hexabenzocoronene (HBC) that self‐organizes into room temperature columnar structure is reported. Tri‐ and di‐ substituted HBC derivatives showed reddish and yellowish green fluorescence under long wavelength (365 nm) UV light illumination in solution as well as in thin films in the liquid crystalline (LC) state at room temperature, respectively. Thermotropic LC behavior of these compounds was studied by differential scanning calorimetry, polarized optical microscopy and small‐ and wide‐angle X‐ray scattering. Tri‐alkoxy derivative was found to self‐organize into a highly ordered columnar rectangular mesophase, while the other (di‐) possessed a columnar hexagonal mesophase, indicating that in spite of their non‐planarity, the aromatic cores in the mesophase are tightly packed to give highly ordered phases. This system is a promising candidate as an active component of organic light emitting devices, due to its facile processability, low band gap, luminescence and exceptionally higher ordered self‐organization behavior in the mesophase derived from X‐ray scattering studies.

Investigations on Preparation and Characterization of Certain Copolyesters

In this paper, we report on the synthesis and characterization of high molecular weight copolyesters from Terephthalic acid, 1, 4 butane diol and Succinic acid /Sebacic acid through a two step process of melt polycondensation using titanium tetra butoxide as catalyst. The synthesized aromatic-aliphatic random copolyesters were characterized by means of FTIR, 1H NMR,13C NMR, Differential Scanning Calorimetry (DSC), X-ray Diffraction (XRD), Gel Permeation Chromatography (GPC) and Scanning Electron Microscope (SEM) studies. The effect of copolymer composition on the physical and thermal properties as well as degradation test was investigated. The degradation test was carried out in alkali medium. The phase behaviour of the polymers was studied by differential scanning calorimetry and optical polarising microscopy. The results revealed that the newly synthesized copolyesters exhibited degradability and thermotropic liquid crystalline behaviour with nematic texture which was revealed by optical polarising microscopy. The Novelty of this work is that the glass transition temperature and melting temperature are above the room temperature for the synthesized polymers. This shows the good thermal stability which results in early processing of liquid crystalline materials.