Mesomorphic Phase Research Articles

A columnar mesophase with high lateral order from a triphenylene-hexa(3,5-dialkoxy)benzoate

This paper describes the synthesis of triphenylene-2,3,6,7,10,11-hexayl hexakis(3,5-dialkoxy)benzoates, bearing hexyloxy (1a) and dodecyloxy tails (1b). These benzoate esters were synthesised in high yields by employing a DCC coupling of the (3,5-dialkoxy) benzoic acid to 2,3,6,7,10,11-hexahydroxytriphenylene. The 3,5-dihexyloxy benzoate 1a, forms a highly ordered columnar mesophase with extensive lateral and very limited columnar order, whereas no mesomorphic phases were observed for the 3,5-didodecyloxy benzoate 1b. In contrast with most benzoate esters of triphenylene, nematic mesophases were not observed for 1.

Formation of a homochiral antiferroelectric ground state in asymmetric bent-shaped molecules

New asymmetric bent-shaped molecules were synthesised and their mesomorphic properties and phase structures investigated by means of electro-optical measurements. All of the compounds formed fluid smectic phases and showed the homochiral antiferroelectric (SmCAPA) ground structure of the B2 phase. Comparing the new molecules with the previously reported classical symmetric bent-shaped molecules, we concluded that the modification of the chemical structure, especially the asymmetrical design of the bent-shaped molecules, is very significant for the interlayer interaction, influencing the formation of a specific polar order in banana phases.

Development of the mesomorphic phase in isotactic propene/higher α-olefin copolymers at intermediate comonomer content and its effect on properties

Several isotactic propene-α-olefin copolymers using 1-octene, 1-dodecene and 1-tetradecene as comonomers (CiPO, CiPDD and CiPTD, respectively) have been synthesized and their structure and thermal/mechanical/viscoelastic properties have been evaluated. At intermediate comonomer molar content ranged from around 4 to 9, the mesomorphic phase is developed under rather mild quenching conditions and independently of length of the comonomer. Thermal and mechanical parameters diminish as α-olefin content increases and their dependence on composition changes as function of existence of three-dimensional monoclinic crystallites or less ordered entities.

Mesomorphic−α-Monoclinic Phase Transition in Isotactic Polypropylene: A Study of Processing Effects on Structure and Mechanical Properties

We report the enthalpy for the mesomorphic to α-monoclinic phase transition in polypropylene under varying thermal treatments. The mesomorphic phase is created by fiber spinning and rapid quenching methods and identified using wide-angle X-ray diffraction and differential scanning calorimetry. Fiber mesomorphs are found to have a 3-fold increase in enthalpy of transition per gram of mesophase compared with our measurements of quenched polypropylene and previous reports of quenched polypropylene. In addition, systematic tensile testing over a range of spin speeds and polymer morphologies reveals that the presence of mesomorphic regions does not correlate with reduced fiber strength as has been previously suggested. Fiber true stress−true strain curves obtained at varying take-up velocities are compared to determine the “tensile strain shift”, which should theoretically provide a measure of molecular orientation. We find that the tensile strain shift correlates with birefringence, thereby providing an alternative method to assess molecular orientation in fibers, an important factor for fiber strength. This approach can prove useful for fibers in which measuring the molecular orientation via birefringence is not an option.

Mesomorphic phase in oriented poly(pentamethylene 2,6-naphthalate)

The mesomorphic structure of poly(pentamethylene 2,6-naphthalate) (PPN) was investigated using a synchrotron X-ray scattering. The PPN fibers cold-drawn from the super-cooled amorphous state showed a smectic mesomorphic structure and further a crystalline phase at high strain. Based on the experimental evidence showing the split of amorphous halo up and down the equator and the conformational constraint suggested by the crystal structure refinement and computation, we suggested the smectic phase as SCA where the mesogens are tilted against the layer surface normal and the tile direction is opposite between the neighboring layers.

Mesomorphic phase transition behaviour of photopolymerisable liquid crystalline triphenylene ether compounds

This report discusses the preparation and the unusual mesomorphism of three homologues of photopolymerisable triphenylene ether compounds. These homologues showed ‘a cold crystallisation’ on heating differential scanning calorimetry curves, and this phenomenon is attenuated with increase methylene units, spacers between the triphenylene core and the terminal photopolymerisable acrylate group. Classical textures of hexagonal columnar (Colh) mesophase were observed by polarising optical microscopy for all three photopolymerisable mesophase compounds described here. Also described is the mesomorphism of their intermediates, hydroxylalkoxytriphenylenes. In some cases, the discotic columnar hexagonal mesophases were confirmed by wide angle X-ray scattering techniques.

Orientational Order of Fluorinated Mesogens Containing the 1,3,2-Dioxaborinane Ring: A Multidisciplinary Approach

Orientational order properties of two fluorinated liquid crystals containing the 1,3,2-dioxaborinane ring have been investigated by means of optical, dielectric, and (13)C and (19)F NMR spectroscopies. The optical birefringence and dielectric anisotropy values determined in the mesomorphic phases were analyzed in terms of well-established theoretical models to obtain the order parameters relative to the principal axis of the polarizability tensor and molecular dipole moment, respectively. A large set of data, including (13)C and (19)F chemical shift anisotropies and (13)C-(19)F and (1)H-(19)F couplings relative to nuclei on the aromatic rings, was acquired in the NMR experiments and analyzed to determine local order parameters (principal order parameter and biaxiality) for different rigid fragments of the mesogen aromatic core using advanced DFT methods for the calculation of geometrical parameters and chemical shift tensors. A critical analysis of the dependence of the order parameters on the data set employed and on the theoretical assumptions and approximations has also been performed. The orientational order parameters obtained using the different techniques are compared and discussed in relation to the reference frame associated with the anisotropic properties monitored.

Colloquium: Laws controlling crystallization and melting in bulk polymers

After the fundamental structure of semicrystalline polymers---platelike crystallites with thicknesses in the nanometer range, embedded in a liquid matrix---was discovered in the late 1950s, attention turned to the mechanism of formation. After intense controversial discussions, an approach put forward by Hoffman and Lauritzen prevailed and was broadly accepted. The picture envisaged by the treatment---platelike crystallites with atomically smooth side faces and a surface occupied by chain folds, growing sideways layer by layer with a secondary nucleation as the rate-determining step---was easy to grasp and yielded simple relationships. The main control parameter is the supercooling below the equilibrium melting point of a macroscopic crystal ${T}_{f}^{\ensuremath{\infty}}$, which determines both the thickness of the crystallites and their lateral growth rate. The impression that the mechanism of polymer crystallization was understood and the issue essentially settled, however, was wrong. Experiments carried out during the last decade on various polymer systems provided new insights which are now completely changing our understanding of such systems. They revealed a number of laws that control polymer crystallization and melting in bulk, showing in particular that the crystal thickness is inversely proportional to the distance to a temperature ${T}_{c}^{\ensuremath{\infty}}$ which is located above the equilibrium melting point, and that crystal growth stops at a temperature ${T}_{\mathrm{zg}}$ which is below ${T}_{f}^{\ensuremath{\infty}}$. Observations indicate that the pathway followed in the growth of polymer crystallites includes an intermediate metastable phase. In a proposed model a thin layer with mesomorphic inner structure forms between the lateral crystal face and the melt. The first step in the growth process is attachment of the coiled chain sequences of the melt onto the mesomorphic layer, which subsequently is transformed into the crystalline state. The transitions between melt, mesomorphic layers, and lamellar crystallites can be described with the aid of a temperature-thickness phase diagram. ${T}_{c}^{\ensuremath{\infty}}$ and ${T}_{\mathrm{zg}}$ are identified with the temperatures of the (hidden) transitions between the mesomorphic and the crystalline phase, and between the liquid and the mesomorphic phase, respectively. Comparing predictions of the model theory with experimental results from small-angle x-ray scattering, optical microscopy, and calorimetry yields in addition to the three equilibrium transition temperatures latent heats of transition and surface free energies.

A Multitechnique Study of Structure and Dynamics of Polyfluorene Cast Films and the Influence on Their Photoluminescence

This article describes the microstructure and dynamics in the solid state of polyfluorene-based polymers, poly(9,9-dioctylfluorenyl-2,7-diyl) (PFO), a semicrystalline polymer, and poly[(9,9-dioctyl-2,7-divinylene-fluorenylene)-alt-co-{2-methoxy-5-(2-ethyl-hexyloxy)-1,4-phenylene vinylene}, a copolymer with mesomorphic phase properties. These structures were determined by wide-angle X-ray scattering (WAXS) measurements. Assuming a packing model for the copolymer structure, where the planes of the phenyl rings are stacked and separated by an average distance of approximately 4.5 A and laterally spaced by about approximately 16 A, we followed the evolution of these distances as a function of temperature using WAXS and associated the changes observed to the polymer relaxation processes identified by dynamical mechanical thermal analysis. Specific molecular motions were studied by solid-state nuclear magnetic resonance. The onset of the side-chain motion at about 213 K (beta-relaxation) produced a small increase in the lateral spacing and in the stacking distance of the phenyl rings in the aggregated structures. Besides, at about 383 K (alpha-relaxation) there occurs a significant increase in the amplitude of the torsion motion in the backbone, producing a greater increase in the stacking distance of the phenyl rings. Similar results were observed in the semicrystalline phase of PFO, but in this case the presence of the crystalline structure affects considerably the overall dynamics, which tends to be more hindered. Put together, our data explain many features of the temperature dependence of the photoluminescence of these two polymers.

A Coupled Differential Scanning Calorimetry and X-ray Study of the Mesomorphic Phases of Monostearin and Stearic Acid in Water

Differential scanning microcalorimetry coupled to Synchrotron small angle X-ray scattering (SAXS) was used to characterize the mesomorphic phases of monostearin — a series of dispersions of monostearin and stearic acid (95:5 w/w) in alkaline water were prepared in the range 5−90% (w/w). Samples were subjected to both melting and cooling regimes from 45 to 81 at 2 °C/min in a Microcalix machine (an X-ray sample chamber with microcalorimetry capabilities), while X-ray spectra and the microcalorimetric trace were being collected simultaneously. Using these two techniques, two-dimensional phase diagrams of the mesomorphic phases (lyotropic and thermotropic liquid crystalline phases as well as the crystalline, hydrated gel phases) of monostearin was created, one for heating and one for cooling, and the typical X-ray diffraction pattern for each of the phases was identified. Polarized light microscopy was also used in an attempt to differentiate and identify the mesomorphic phases. Furthermore, the largest d-sp...

Influence of structural organization on tensile properties in mesomorphic isotactic polypropylene

Abstract The effects of annealing on the structure and mechanical properties of mesomorphic isotactic polypropylene have been investigated using wide-angle and small-angle X-ray scattering and rheo-optics in addition to tensile tests. Young's modulus of mesomorphic phase was estimated to be 5 GPa using Takayanagi model. The α-crystallitic iPP prepared by annealing the quenched mesomorphic iPP was transparent because of the absence of spherulitic structure. It was found that the mechanical yielding of α-crystallitic iPP is dominated by the plastic flow of crystalline structural units whereas the yield process of α-spherulitic iPP quenched at 80 °C is caused by the fracture or fragmentation of crystalline structural units.

Hierarchical Organization of Poly(ethylene oxide)-block-poly(isobutylene) and Hydrophobically Modified Fe2O3 Nanoparticles at the Air/Water Interface and on Solid Supports

Langmuir monolayers and Langmuir-Blodgett (LB) film morphologies of block copolymers and hydrophobically modified iron oxide nanoparticles were studied by surface pressure-mean molecular area (pi-mmA) measurements and by tapping mode atomic force microscopy (AFM). The amphiphilic diblock copolymers consisted of a hydrophilic poly(ethylene oxide) (PEO) block and a hydrophobic poly(isobutylene) (PIB) block. The pi-mmA isotherm of PEO(97)-b-PIB(37) (the subscripts refer to the respective degrees of polymerization) at the air/water interface had an extended plateau reflecting the extension of PEO chains into the water subphase at a surface pressure of 10 mN.m(-1), which is absent for the more hydrophobic PEO(19)-b-PIB(130). Iron oxide (Fe(2)O(3)) nanoparticles capped with oleic acid ligands as the shell were dispersed in the amphiphilic block copolymers at the air/water interface to prevent macroscopic aggregation of the particles. When the nanoparticles were mixed with PEO(97)-b-PIB(37), using a particle to polymer chain ratio of 1:100, macroscopic aggregation of the nanoparticles was not observed, and the pi-mmA isotherm was dominated by PEO(97)-b-PIB(37). Monolayers of block copolymers were transferred at different surface pressures from the air/water interface to hydrophilic silicon substrates using the Langmuir-Blodgett technique. The AFM images of PEO(97)-b-PIB(37) LB films depicted not only the typical finger-like morphology of the crystallized PEO blocks but also PIB blocks arranged in vertical columns growing perpendicular to the substrate surface. The columns are characteristic for PEO(19)-b-PIB(130) LB films after transfer at high surface pressures and can be assigned to a mesomorphic PIB phase with ordered chains. Finally, it was observed that small clusters of a few Fe(2)O(3) nanoparticles occupy the top of PIB phases after compression and transfer of the block copolymer nanoparticle mixtures to solid supports.

Studies on the influence of molecular weight and isotacticity of polypropylene on the formation of mesomorphic phase

AbstractPolypropylene (PP) blends with various molecular weight and isotacticity were prepared through solution blending and subjected to rapid melt quenching. Structural changes in the PP matrix during mesomorphic phase formation were measured by FTIR spectroscopy and wide‐angle X‐ray diffraction measurements. The blends with different molecular weight and isotacticity provided the pathway to understand their influence on mesomorphic phase formation. It is observed that low molecular weight PP with low isotacticity forms mesomorphic phase, whereas high molecular weight and low isotactic PP does not lead to the formation of mesomorphic phase. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009

側鎖にビフェニル基をもつポリ(a-フルオロメチルアクリレート）の合成と液晶相転移

側鎖にビフェニル基をもつポリ(a-フルオロメチルアクリレート）の合成と液晶相転移

Formation of the New Trigonal Polymorph in iPP−1-Hexene Copolymers. Competition with the Mesomorphic Phase

The polymorphic structure and the thermal transitions of several iPP−1-hexene copolymers have been analyzed by performing DSC and variable-temperature X-ray diffraction experiments. Special attention has been paid to the range of “intermediate” comonomer contents, between around 8 and 12 mol %, where the new trigonal form of iPP starts to be observed. It was found that the mesomorphic modification is also easily obtained in that comonomer range, so that the possibility of such mesomorphic phase acting as a transient structure of the trigonal form was entertained. However, the results have clearly shown that the mesomorphic modification is not acting as such transient structure, and rather it is a competitor (as well as the α crystals) for the formation of the trigonal phase.

Synthesis, structure, and phase behavior of new chiral liquid‐crystalline polysiloxanes based on mesogenic menthyl monomers

AbstractSix new chiral monomers (M1–M6), and their corresponding side chain polymers (P1–P6) containing menthyl groups were synthesized. The chemical structures of M1–M6 were characterized with FTIR and 1H NMR. The structure–property relationships of the monomers and polymers obtained are discussed. The mesomorphic properties and phase behavior were investigated by differential scanning calorimetry, thermogravimetric analysis, polarizing optical microscopy, and X‐ray diffraction measurements. Some compounds containing menthyl groups formed mesophase when a flexible spacer was inserted between the mesogenic core and the menthyl groups by reducing the steric hindered effect. The monomers M1, M4, and M5 did not reveal mesomorphic properties because of the weaker rigid core or the longer flexible terminal groups, whereas M2, M3, and M6 all revealed cholesteric phase. Except P4 and P5, the homopolymers P1–P3 and P6 showed a smectic A phase. In addition, melting, glass transition temperature, or clearing temperature increased, and the mesophase temperature range widened with increasing the rigidity of mesogenic core or decreasing the length of the flexible spacer. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009

Synthesis and phase behavior of new cholesteric liquid‐crystalline copolymers containing chiral mesogenic groups derived from menthol derivatives

AbstractThe synthesis of a new chiral mesogenic monomer (M1), a nematic monomer (M2), and a series of side chain cholesteric copolymers (P2–P6) containing the mesogenic menthyl groups is described. The chemical structures of the compounds were confirmed by FTIR and 1H NMR. The mesomorphic properties and phase behavior were investigated by differential scanning calorimetry, thermogravimetric analysis, and polarizing optical microscopy. M1 showed an enantiotropic cholesteric phase, and M2 revealed a nematic phase. The homopolymers P1 and P7, respectively, displayed a chiral smectic A (SA) phase and a nematic phase, while the copolymers P2–P6 exhibited the Grandjean texture of the cholesteric phase. Tg, Ti, and ΔT of P1–P7 increased with increasing the concentration of M2 in the polymers. All of the obtained polymers displayed very good thermal stability and the wide mesophase temperature range. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008

Mesomorphic Phase of Poly(butylene-2,6-naphthalate)

The mesomorphic phase of poly(butylene-2,6-naphthalate) (PBN) has been studied using wide-angle X-ray diffraction (WAXD) and differential scanning calorimetry (DSC). It was found that PBN showed a mesomorphic phase when it was rapidly quenched from the molten state to 0 °C. The mesomorphic PBN was nearly transparent solid in appearance and its structure in WAXD scale was an intermediate one between amorphous and crystal having smectic periodicity. With increasing the temperature, a portion of amorphous remaining in the quenched PBN transformed into the mesomorphic phase above 48 °C, and then the mesomorphic phase began to transform into the α-crystal above 71 °C. We propose that the mesomorphic phase of PBN has a glass transition temperature T g meso at 65 °C besides the normal glass transition temperature Tg for the isotropic glass at 41 °C.

Cholesteric Liquid-Crystalline Thermosets Derived from Side-Chain Liquid-Crystalline Epoxy Oligomers

A series of side-chain liquid crystalline (LC) oligomers bearing glycidyl ether groups were synthesized with cholest-5-en-3-ol(3 β)-4-(2-propenyloxy) benzoate, octyl 4-(4-allyloxy-benzoyloxy)-benzoate and epoxy monomer allyl glycidyl ether. The chemical structures and LC properties of the monomers and oligomers were characterized by use of various experimental techniques. All the chiral LC oligomers showed cholesteric mesophase with very wide mesophase temperature ranges. All the synthesized LC oligomers were cured with 4,4'-diaminodiphenylmethane at the same curing conditions. The thermal behaviors, mesomorphic phase and optical properties of the thermosets were characterized. The synthesized thermosets have high thermal stability. The cholesteric phases of LC oligomers were frozen in the polymer networks. Compared with those of corresponding oligomers, the reflection located at wide angles of thermosets became more diffuse, and the peak intensity decreased in X-ray diffraction analysis. The selective light reflection maximum λmax of the thermosets at room temperature shifted slightly to short wavelengths as the LC monomer bearing cholesteryl component was increased, indicating that the helical pitch P becomes shorter due to more chiral groups in the polymer network systems. The temperature dependences of both reflection wavelength and optical rotation under the influence of the crosslinking reaction were also investigated.

Stabilization of the mesomorphic phase in a self-assembled two-component system

We reported here the two-component self-assembling building blocks capable of forming lyotropic liquid crystal and liquid-crystalline physical gel. One of the components has a molecular characteristic of C 3 -symmetrical trisureas containing three azobenzene groups, which can form liquid-crystal phase in a temperature range of 133–215 °C. Another one has a trisamide core, which can self-aggregate to fibrous network through hydrogen bonds of amide moieties. The mixture of these two components performs lyotropic liquid crystal as well as liquid-crystalline physical gel in a temperature range larger than that of sole compound, suggesting that the cooperation of hydrogen bonds between these components stabilizes the mesophase of the assembly. The mechanism of formation of the mesophase was investigated by infrared spectra and small-angle X-ray scatterings.