Thermotropic Liquid Crystalline Research Articles

Effect of Molecular Weight on Mesomorphic Behavior of Side-Chain Liquid-Crystalline Azopolymers

ABSTRACTThree methacrylic polymers bearing (phenylene)azobenzene moieties in the side-chain were synthesized via free-radical polymerization of monomer (E)-6-(4-((3’-cyano-4’-(hexyloxy) -[1,1’- biphenyl]-4-yl) diazenyl) phenoxy) hexyl methacrylate using 1, 5 and 10 mol% of 1,1’-azobis(cyclohexanecarbonitrile) (ABCN) as initiator. The chemical structures of monomer and polymers were confirmed by 1H NMR and FT-IR spectroscopies. Analysis by gel permeation chromatography (GPC) showed average molecular weights (Mw) of 1.0x105, 7.3x104, and 4.5x104 g/mol for polymers P1%, P5%, and P10%, respectively. These results indicate a clear dependence of the Mw on the amount of initiator used; the higher the amount of ABCN, the lowest the molecular mass. Thermotropic liquid-crystalline properties were analyzed by differential scanning calorimetry (DSC) and polarized optical microscopy (POM). All polymers showed a liquid-crystalline behavior over a wide range of temperatures (>100°C) displaying smectic type mesophases. A small shift (around 8°C) upwards in the clearing temperature was observed on increasing the molecular masses from P10% to P1%. The trans-cis photo-isomerization of polymers was studied in solution and in thin films by UV-Vis spectroscopy. High cis-isomer contents in solution (>90%) were reached in relative short irradiation times.

Ionic conductivity probed in main chain liquid crystalline azobenzene polyesters

ABSTRACTThree main chain thermotropic liquid crystalline (LC) azobenzene polymers were synthesized using the azobenzene twin molecule (P4P) having the structure Phenylazobenzene‐tetraethyleneglycol‐Phenylazobenzene as the AA monomer and diols like diethylene glycol, tetraethylene glycol (TEG), and hexaethylene glycol as the BB comonomer. Terminal C(O)OMe units on P4P facilitated transesterification with diols to form polyesters. All polymers exhibited stable smectic mesophases. One of the polymers, Poly(P4PTEG) was chosen to prepare composite polymer electrolytes with LiCF3SO3 and ionic conductivity was measured by ac impedance spectroscopy. The polymer/0.3 Li salt complex exhibited a maximum ionic conductivity in the range of 10−5 S cm−1 at room temperature (25 °C), which increased to 10−4 S cm−1 above 65 °C. The temperature dependence of ionic conductivity was compared with the phase transitions occurring in the sample and it was observed that the glass transition had a higher influence on the ionic conductivity compared to the ordered LC phase. Reversible ionic conductivity switching was observed upon irradiation of the polymer/0.3 Li salt complex with alternate UV and visible irradiation. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015, 53, 629–641

Methacrylate Copolymers with Liquid Crystalline Side Chains for Organic Gate Dielectric Applications.

PSS electrodes because of the increased solvent resistance. The LC side chains reduce the ability for cross-linking resulting in decreased breakdown field strengths.

Enhanced thermal and mechanical properties of polyimide composites by mixing thermotropic liquid crystalline epoxy grafted aluminum nitride

In this paper, we have fabricated thermotropic liquid crystalline with epoxy groups grafted AlN nanoparticles (LCE-g-AlN) and then incorporated these into polyimide (PI) matrix to obtain the composites. The structure of LCE-g-AlN was charactered by Fourier-transform infrared (FT-IR), X-ray photoelectron spectroscopy (XPS), thermogravimetric analyses (TGA), differential scanning calorimetry (DSC) and scanning electron microscopy (SEM). The morphology and thermal properties of composites were systematically investigated. The morphology of the PI/LCE-g-AlN composites performed by scanning electron microscopy (SEM) indicating a homogeneous distribution of LCE-g-AlN nanoparticles in the PI matrix. Moreover, the value of Young's modulus and tensile strength of the PI composites was increased by 78.3 % and 22.7 % in comparison with neat PI, respectively. The value of storage modulus of the PI composites achieved 7897 MPa with the incorporation of 10 wt.%, which increase 159.6 % compared with the neat PI (3035 MPa).

Structure–property relationship in charge transporting behaviour of room temperature liquid crystalline perylenebisimides

A homologous series of pentadecyl phenol functionalized perylenebisimide (PBI) terminated with trialkoxy gallate esters was synthesized, where the terminal alkyl chain length was varied from n = 4 to 12 (PBI-En). The thermotropic liquid crystalline (LC) characteristics of the molecules were analyzed using differential scanning calorimetry (DSC), polarized light microscopy (PLM) combined with variable temperature wide angle X-ray diffraction (WXRD) techniques. A clear odd–even oscillation was observed in the melting as well as isotropization enthalpies as a function of alkyl spacer length in the terminal gallate unit, with the even spacers exhibiting higher values. The higher members of the series with n > 8 exhibited thermotropic liquid crystalline textures in the PLM, which remained stable until room temperature. The nature of the LC phase was identified to be columnar rectangular and columnar hexagonal based on detailed analysis of the WXRD pattern recorded in the LC phase. The WXRD pattern of the room temperature LC frozen samples indicated a nearly constant intra columnar stack distance of ∼3.7 A for all the members. The space-charge-limited current (SCLC) values of the LC frozen sample films were analyzed for dependence of the bulk mobility estimate on the nature of the LC phase. The columnar hexagonal phase exhibited a mobility value one order (10−3 cm2 V−1 s−1) higher than that of crystalline (10−4 cm2 V−1 s−1) and two orders higher than that of columnar rectangular phase (10−5 cm2 V−1 s−1), indicating a strong dependence of packing on bulk mobility.

A room temperature discotic mesogenic dyad based-on triphenylene and pentaalkynylbenzene

A facile synthesis of a novel room temperature discotic mesogenic dyad based on triphenylene and pentaalkynylbenzene linked via flexible alkyl spacer is reported. The thermotropic liquid crystalline (LC) property of the compound was investigated by polarizing optical microscopy (POM), differential scanning calorimetry (DSC), and X-ray diffractometry (XRD). The LC property of the dyad was further manipulated by preparing charge transfer (CT) complexes with trinitrofluorenone (TNF). The compound self-assembles into a columnar hexagonal mesophase and exhibits an excellent fluorescent emission property which has possible potential for various opto-electronic applications.

Effects of ionic group incorporation into model polypeptide, poly(γ-benzyl-L-glutamate) (PBLG)

Effects of incorporation of ionic groups and ionic interactions to a model polypeptide, poly(γ-benzyl-L-glutamate) (PBLG), are studied. Partial conversion of γ-benzyl-L-glutamate residues to glutamic acid residues does not change molecular conformation (α-helix) and shows little change in properties. By contrast, partial conversion to sodium glutamates (ionic groups) leads to conversion from a rigid rod to a semi-flexible rod at low ion contents and causes significant changes in thermal stability and birefringence. In solution, lyotropic liquid crystalline behavior of PBLG is lost at ion content as low as 3.2 mol %. In solid, birefringence is still observed at this ion content, suggesting thermotropic liquid crystallinity of this ionic PBLG. Molecular composites made of ionic PBLG as a reinforcer and poly(4-vinylpyridine) (PVP) as a matrix polymer show significant enhancement in strength and toughness as a result of ion-dipole interactions between the component polymers.

Synthesis and Surface Properties of Novel Gemini Imidazolium Surfactants

AbstractFive new Gemini imidazolium surfactants were synthesized from imidazole and 1‐bromoalkane (C8, C10, C12, C14, C16) to get 1‐alkylimidazole, which was further reacted with 1,3‐dichloropropan‐2‐ol to form the surfactant molecule, 1,1′‐(propane‐1,3‐diyl‐2‐ol) bis(3‐alkyl‐1H‐imidazol‐3‐ium) chloride. The structures of the five new surfactants and intermediates were characterized by 1H‐NMR, 13C‐NMR and IR spectra. Thermal properties of the five new surfactants were studied with thermogravimetric analysis and differential scanning calorimetry, the five new surfactants showed a transition from a crystalline phase to a thermotropic liquid–crystalline phase at around ca. 100 °C, which transformed to an isotropic liquid phase at around ca. 165 °C. The five new surfactants critical micelle concentrations (CMC) in the aqueous solutions were determined by surface tension and electrical conductivity methods. The surface tension measurements provided a series of parameters, including critical micelle concentration (CMC), surface tension at the CMC (γCMC), adsorption efficiency (pC20), and effectiveness of surface tension reduction (πCMC). In addition, with application of the Gibbs adsorption isotherm, maximum surface excess concentration (Γmax) and minimum surface area/molecule (Amin) at the air–water interface were obtained. The parameters β (degree of counterion binding to micelles), ΔGadsθ (Gibbs free energy of adsorption), and ΔGmicθ (Gibbs free energy change of micellization) were also derived. The results indicated that the five new Gemini surfactants exhibited very low CMC and a good efficiency in lowering the surface tension of water. The foamability and foam stability of the five new surfactants were also examined at different CMC.

Polarimetry-controlled fluorescent color in oriented LC biopolyesters

Oriented films of the thermotropic liquid-crystalline (LC) polymer, poly{3-benzylidene amino-4-hydroxybenzoic acid (3,4-BAHBA)-co-trans-4-hydroxycinnamic acid (4HCA)} (Poly(3,4-BAHBA-co-4HCA)), were prepared by shearing the LC melt. X-Ray and polarized microscopy analyses indicated that the main chains were oriented perpendicularly to the shear direction, and the benzylidene amino side chains were parallely oriented. Furthermore, the oriented film showed polarized fluorescence in which the analyzer rotation changed the emission color when the polarizer was set perpendicular to the sheared direction. Open image in new window

Thermotropic Polyesters from 2,5-Furandicarboxylic Acid and Vanillic Acid: Synthesis, Thermal Properties, Melt Behavior, and Mechanical Performance

In this work, we address the synthesis of novel aromatic–aliphatic biobased polyesters showing thermotropic behavior in the melt. Successful incorporation of different biobased monomers such as 2,5-furandicarboxylic acid (2,5-FDCA), suberic acid (SuA), and vanillic acid (VA) in thermotropic liquid crystalline polymers (TLCPs) is made possible by performing synthesis at low temperatures. The chemical structures, molecular weights, phase transitions, thermal behavior, and mechanical performance of the synthesized polymers are studied using polarization optical microscopy, WAXD, DSC, TGA, DMTA, solid-state NMR spectroscopy, rheology, and tensile tests. It is shown that the incorporation of the rigid, aromatic 2,5-FDCA moiety enhances the formation of blocky copolymers, whereas the VA moiety tends to decrease the block formation. However, when combined, nonblocky TLCPs containing 2,5-FDCA and VA with high aromatic content can be obtained. These materials show a low temperature transition from the crystalline ...

Skeletal cubic, lamellar, and ribbon phases of bundled thermotropic bolapolyphiles.

A series of T-shaped polyphilic molecules composed of a rigid linear biphenyl core with a polar glycerol group at each end and one swallow-tail semiperfluorinated lateral chain were synthesized and their thermotropic liquid crystalline (LC) phases were investigated by X-ray diffraction, calorimetry, and microscopy. The compounds have a long alkyl spacer between the aromatic core and the fluorinated C(n)F(2n+1) ends, where n = 4, 6, 8, and 10. Upon melting, all compounds start with lamellar LC phases, followed on heating by a rectangular columnar ribbon phase with c2mm symmetry. Unusually, a ribbon is a flat bundle of molecular cores highly aligned parallel to the ribbon axis. On further heating, for n = 8 and 10, this phase is succeeded by a bicontinuous cubic phase with Ia3d symmetry. This is a new variant of the "gyroid" phase, with axially oriented rod-like molecular cores forming the skeleton of the two infinite networks and junctions separated by exactly two molecular lengths. In this tricontinuous core-shell structure (aromatic-aliphatic-perfluoroalkyl), the polar glycerol domains of appreciable size, contained within the skeleton, can be considered as micellar.

Design of Amphiphilic Zwitterions Forming Liquid-Crystalline Phases and Effects of Lithium Salt Addition on Their Phase Behavior

Abstract We prepared pyridinium-based amphiphilic zwitterions and examined their liquid-crystalline (LC) phase behavior in the presence and absence of lithium salts. Addition of lithium salts induced nanosegregated LC phases such as bicontinuous cubic phase and smectic phase depending on the anion species of the lithium salts. For example, an equimolar mixture of dodecylcarbamoyl-1-(4-sulfobutyl)pyridinium betaine and lithium bis(trifluoromethanesulfonyl)imide (LiTf2N) exhibited a bicontinuous cubic phase between 40 and 100 °C. The exhibition of these nanosegregated phases was attributed to the formation of an ionic liquid-like ion pair composed of the pyridinium cation and the Tf2N anion. The preferential interaction between the pyridinium cation and the Tf2N anion was confirmed with Raman spectroscopic measurement. Moreover, the amphiphilic zwitterions were found to show not only thermotropic LC behavior but also lyotropic LC behavior in the presence of polar solvents such as protic ionic liquids. The results presented here indicate that the combination of amphiphilic zwitterions and suitable additive ions is a potential method to construct nanostructured LC materials showing tuneable phase behavior.

Synthesis of Hydrophobic Carbohydrate Polymers and Their Formation of Thermotropic Liquid Crystalline Phases.

The first synthesis of enantiopure glucose octyl ether polyamido-saccharides (GOE-PAS) with a defined molecular weight and narrow dispersity is reported using a controlled anionic ring-opening polymerization of a glucose-derived β-lactam sugar monomer possessing octyl ether chains. This new polymer structure is characterized by NMR, infrared (IR), optical rotation, gel permeation chromatography (GPC), and thermogravimetric analysis (TGA). At room temperature, the polymers form lamellar (Lam) phases. Upon heating to mild temperatures (ca. 60 °C), the shortest polymer shows a direct transition to the isotropic (Iso) liquid state, while the longer polymers give rise to a hexagonal columnar (Colh) phase before becoming isotropic at higher temperatures (ca. 120 °C).

Monolayer Properties of Asymmetrically Substituted Sexithiophene

We present a structural comparison of monolayers on a SiO2 substrate of two asymmetrically substituted sexithiophenes (6T). Molecule 1 consists of 6T with a branched alkyl chain at one end only and shows a crystalline structure. In molecule 2, the bifunctional 6T has in addition at the other end a linear alkyl chain. It displays thermotropic liquid crystalline (LC) behavior. Both compounds form readily single molecular layers from solution. Remarkably, full monolayer coverage can be achieved before multilayer growth starts. LC properties promote preordering near the interface as well as exchange of molecules between the growing domains, thus regulating the domain sizes. As a result, the LC compound 2 forms single-molecule islands with larger domain sizes compared to compound 1. Surface X-ray investigations indicate that the 6T cores are tilted relative to the layer normal. The tilt angle is as large as 54° for compound 2 compared to 28° for compound 1. For molecule 2, interfacial constraints and packing requirements because of the asymmetric substitution cause a rather loosely organized core structure.

An Easy Route to Lower-Destructive and Highly Functionalized Multi-Walled Carbon Nanotubes with Thermotropic Liquid Crystalline Polymer on a Large Scale

An easy and less-destructive method has been developed to highly functionalize multi-walled carbon nanotubes (MWCNTs) with thermotropic liquid crystalline polymer (TLCP) via an elimination reaction between TLCP terminated phenolic hydroxyl groups and p-benzyl chloride groups of active poly(4-chloromethyl styrene) (PCMS) on the surface of tubes, where MWCNTs were functionalized with PCMS through the esterification reaction of carboxylate of the former and p-benzyl chloride groups of the latter in the presence of a phase-transfer catalyst. Differential scanning calorimetry (DSC) and polarized optical microscopy (POM) confirmed liquid crystal behavior of TLCP. The high density of covalent bonding between TLCP and nanotubes was confirmed by FTIR and Raman, resulting in a high grafting efficiency, as high as 18 wt% of TGA. Microscopic observations clearly displayed thick TLCP layers formed on the MWCNT surface.

Optical absorption, induced bleaching, and photoluminescence of CdSe nanoplatelets grown in cadmium octanoate matrix

CdSe nanoparticles (NPs) are chemically synthesized in thermotropic ionic liquid crystalline (LC) phase of cadmium octanoate that was used as a nanoreactor. The nanocomposite samples are obtained by the rapid cooling of the LC phase to room temperature. Observed doublet structure in absorption spectra of the nanocomposites is characteristic for the two-dimensional CdSe nanoplatelets (NPLs). The thicknesses of the CdSe NPLs are 1.6, 1.9 and 2.3 nm as determined from the absorption spectra, and correspond to 4, 5 and 6 CdSe monolayers, respectively. Induced simultaneous bleaching of the doublet components observed under femtosecond laser excitation, as well as photoluminescence spectra and their kinetics are found compatible with the model of excitons with heavy- and light-hole valence bands confined in nanoplatelets.

주사슬에 X-자 모양의 메소젠기를 갖는 액정폴리에스터의 합성 및 성질

주사슬에 X-모양의 메소젠기를 갖는 액정폴리에스터 시리즈가 단위체인 2,5-디(4-치환된 벤조에이트)하이드로퀴논과 4,4'-디카르복시-1,8-디페녹시옥테인으로부터 용액중합에 의해 합성되었다. 합성된 중합체의 구조와 물성들은 <TEX>$^1H$</TEX>-NMR, FT-IR, DSC, TGA, POM, WXRD를 이용하여 조사되었다. 1,1,2,2-테트라클로로에탄 내에서 측정된 중합체의 고유점성도(<TEX>${\eta}_{inh}$</TEX>)는 0.35~0.66 dL/g로 측정되었으며, 본 실험에서 용해도 조사에 사용된 대부분의 유기용매에 잘 용해되었다. 모든 중합체들은 비교적 낮은 용융전이온도(<TEX>$T_m$</TEX>)와 결정성을 나타내었으며, <TEX>$T_m$</TEX> 이상으로 가열했을 때 열방성 네마틱 액정성을 보였다. 중합체의 이러한 특성은 주사슬에 결합되어 있는 벌키한 4-치환된 벤조에이트기에 때문인 것으로 보인다. A series of liquid crystalline polyesters containing X-shaped mesogenic groups in main chain were synthesized through the solution polymerization of 2,5-di(4-substituted benzoate)hydroquinones and 4,4'-dicarboxy-1,8-diphenoxyoctane. The structures and properties of synthesized polymers were investigated by <TEX>$^1H$</TEX>-NMR, FT-IR, differential scanning calorimetry (DSC), thermogravimetry analysis (TGA), polarized optical microscopy (POM) and wide angel X-ray diffraction (WXRD). Inherent viscosities (<TEX>${\eta}_{inh}$</TEX>) of polymers were measured between 0.35 and 0.66 dL/g in 1,1,2,2-tetrachloroethane, and they were easily soluble in most of organic solvents used for this experiment. All polymers revealed relatively low melting transition temperature (<TEX>$T_m$</TEX>) and crystallinity, and also showed thermotropic nematic liquid crystallinity when they were heated to their melting temperatures. These properties of polymers were presumably due to the presence of the bulky substituting groups on the hydroquinone unit in mesogenic group.

Metal-centered polyoxometalates encapsulated by surfactant resulting in the thermotropic liquid crystal materials

Waugh- and Silverton-type polyoxometalates (POMs) K3(NH4)3[MnMo9O32] and H8[CeMo12O42] are enwrapped by dioctadecyldimethylammonium (DODA+) forming the surfactant-encapsulated POMs (SEPs) (DODA)6[MnMo9O32]·16H2O (DODA-MnMo9) and (DODA)8[CeMo12O42]·9H2O (DODA-CeMo12), which exhibit typical thermotropic liquid-crystalline properties. Here, the Waugh- and Silverton-type polyoxoanions centered by metal cation were firstly introduced into liquid crystal materials. The chemical composition of these SEP complexes was determined by IR spectra, elemental analysis and TG analysis. Also, the polarized optical microscopy, differential scanning calorimetry (DSC), variable temperature X-ray diffraction (VT-XRD) and transmission electron microscopes (TEM) were performed to characterize their liquid-crystalline behavior.

Phosphorus-containing thermotropic liquid crystalline polymers: a class of efficient polymeric flame retardants

The flame retardation of polymeric materials can be achieved by addition of small-molecule flame retardants. However, traditional small molecule flame retardants exhibit practical drawbacks during application, such as migration problems, the deterioration of polymer performance, as well as potential persistence, bio-accumulation and toxicity (PBT), etc. High molecular weight molecules have been found to be less accessible by living organisms and so have an automatically lower PBT profiles than small molecules. Phosphorus-containing thermotropic liquid crystalline polymers have proven to be a class of efficient polymeric flame retardants, which can overcome the aforementioned drawbacks of small molecules and have potential industrial applications to replace some of the existing small molecule flame retardants. The recent relevant developments are reviewed in this article.

Mesomorphic azomethine complexes of Iron(III) based on 4,4′-dodecyloxybenzoyloxybenzoyl-4-salicylidene-2-aminopyridine

A new series of liquid crystalline (LC) complexes Fe(III) based on azomethine 4,4′-dodecyloxybenzoyloxybenzoyl-4-salicylidene-2-aminopyridine with counter-ions PF6−, NO3−, Cl−, BF4−, ClO4−, CNS− and SO42– was synthesised. According to elemental analysis, FT-IR, 1H-NMR and mass spectrometry (MALDI ToF), it was found that bi(ligand) Fe(III) complexes were formed with octahedral packing of the metal ion. The presence of the counter-ion in the complexes was confirmed by Infrared spectroscopy. The thermotropic LC properties were investigated by differential scanning calorimetry (DSC) and polarising optical microscopy (POM). All the seven complexes in this series exhibit thermotropic mesophases.