Mesophase preparation

These methods, described above, are to produce material (still loosely called mesophase) which essentially is a feedstock for other process developments. This "mesophase" prepared at temperatures below normal carbonization temperatures can be called low temperature mesophase pitch (LTMP). The term mesophase pitch has crept into the vocabulary of this subject and is thought to refer mainly to mesophase as a feedstock. Its anisotropy can be detectable by polarized light optical microscopy. 

The spatial geometry of disclination reactions in bulk mesophase has recently been presented by Zimmer and Weitz (29) Working with coarse-structured mesophase prepared by lengthy pyrolysis of A240 petroleum pitch at 400°C, they defined the disclination arrays on a succession of polished sections spaced at about 7 ym. In this way a +tt disclination was traced through a branching point (i.e., a reaction point) to form a -tt and a +2tt disclination. Thus a reaction... 

The lyotropic mesophase prepared from a polymer dissolution in a mixture of solvents is an interesting case. At a given polymer concentration, the organization of macromolecules is governed by the surface of the droplets and intermolecular Interactions. It can be varied by changes in the relative proportions of the solvents. 

Mesophases prepared by dissolution of the copolymer in a preferential solvent for the poly(vinylpyridine) block (acrylic acid, nitromethane, dfoxane, octanol, methylethyl ketone, ethyl acetate, vinyl acetate, styrene and methyl methaaylate) and dry copolymers obtained by slow evaporation of the solvent from the mesophases have been studied by low-angle X-r diffraction electron microscopy Copolymers of isoprene and vinylpyridine exhibit cylindrical hexagonal or lamellar structures dependii upon their comi siton.The influence of the nature, concentration, and polymerization of the solvent, molecular weight and composition of the copolymer, microstructure of the polyisoprene block, and position of the nitrogen atom in the vinylpyridine block on the values of the geometrical parameters of the periodic structures have been establidied ... 

Although the mesophases prepared by Liu et al. [4] did not show X-ray reflections in the wide-angle range (> 5 °2Q), the solids showed an enhanced thermal stability [3-5] in comparison with conventional mesoporous materials. Following this approach we will describe here the crystallization of ZSM-5 seeding gel in the presence of the cationic surfactant cetyltrimethylammonium bromide known as structure directing agent for different mesophases [1]. 

The mesophase prepared by this route is mainly insoluble in solvents like pyridine or quinoline. Thus, extraction techniques have been extensively used to determine the degree of the isotropic pitch/mesophase conversion and then the reaction kinetics. At 350 C, the formation of the mesophase is extremely slow. One week is required to achieve a 40 wt.% concentration of mesophase. At 400-450°C, one to forty hours are required to achieve a 50 wt.% concentration of mesophase. Finally, temperatures above 500 C are considered undesirable due to the risk of coke formation. The formation of pyridine and quinoline extractables, i.e., mesophase, has been reported to follow first order kinetics. 

In general, vesicles exhibit a phase transition behavior that is very different from that observed with multilamellar (liposomes or lamellar mesophase) preparations [90-93]. Suurkuusk et al. [92] found that unsonicated (multilamellar liposome) and sonicated (vesicle) samples of dimyristoylphosphatidylcholine exhibit different heat capacity maxima (Fig. 9) [94]. This difference implies a change in the organization of the phospholipids upon sonication. ESR and NMR spectroscopy showed that the small radius of curvature of the vesicles leads to less efficient packing and to greater freedom of motion of the hydrocarbon chains. The phase diagram of reversed vesicles was studied by DSC by Kunieda et al. [95],... 

The separation of Hquid crystals as the concentration of ceUulose increases above a critical value (30%) is mosdy because of the higher combinatorial entropy of mixing of the conformationaHy extended ceUulosic chains in the ordered phase. The critical concentration depends on solvent and temperature, and has been estimated from the polymer chain conformation using lattice and virial theories of nematic ordering (102—107). The side-chain substituents govern solubiHty, and if sufficiently bulky and flexible can yield a thermotropic mesophase in an accessible temperature range. AcetoxypropylceUulose [96420-45-8], prepared by acetylating HPC, was the first reported thermotropic ceUulosic (108), and numerous other heavily substituted esters and ethers of hydroxyalkyl ceUuloses also form equUibrium chiral nematic phases, even at ambient temperatures. 

Mochida, I, Shimizu, K., Korai, Y., Sakai, Y., Fujiyama, S., Toshima, H. and Hono, T., Mesophase pitch catalytically prepared from anthracene with HF/BF3, Carbon, 1992, 30(1), 55 61. 

As indicated above in chiral mesophases, the introduction of a functional group in mesogenic stmctures offers the opportunity to achieve functional LCs. With this aim, mesomorphic crown-ether-isocyanide-gold(I) complexes (26) have been prepared recently [38]. The derivatives with one alkoxy chain show monotropic SmC mesophases at or close to room temperature. In contrast, the complexes with three alkoxy chains behave as monotropic (n = 4) or enantiotropic (n > 4) LCs. The structure of the mesophases could not be fully eluddated because X-ray diffraction studies in the mesophase were unsuccessful and mesophase characterization was made only on the basis of polarized optical microscopy. These complexes are luminescent not only in the solid state and in solution, but also in the mesophase and in the isotropic liquid state at moderate temperatures. The emission spectra of 26a with n=12 were... 

An example of ionic mesomorphic imidazolium cyanoaurate derivative (32) has been prepared displaying a SmA mesophase in the range of 66-112 °C [61]. 

This species has been used as precursor of nanogold particles by electrodeposition. When the electrodeposition is induced from the isotropic state at 117 °C, the nanoparticles obtained are nanodots aggregated in a spherical-like shape. In contrast, the morphology of the nano particles prepared from the SmA mesophase at 111 °C consist of leaf-like forms interlocked in rosettes. 

The nematic nanoparticies have been prepared by a two step synthetic process. First, gold nanopartides are covered with an alkylthiol monolayer (hexyl- and dodecylthiol) in a second step, the alkylthiol-nanoparticles are reacted with the functionalized thiol mesogen in dichloromethane at room temperature to obtain the monolayer-protected liquid crystal gold nanopartides. These materials are chemically stable and display a nematic mesophase at room temperature [67, 68]. Other examples include liquid crystal gold nanopartides functionalized by hexaalkoxy-substituted triphenylene [69]. 

Materials used in the activation with KOH include high volatile bituminous coal C, coal semi-coke CS, pitch mesophase PM, pitch semicoke PS and commercial activated carbon AC. The semi-cokes CS and PS were produced by the heat treatment of corresponding parent materials at 520°C with a heating rate of 5°C/min and 2 hours soaking time. The preparation of mesophase PM comprised the soaking of coal-tar pitch at 450°C for 7 h with a continuous stirring. All the treatments were performed under argon in a vertical Pyrex retort of 45 mm diameter. 

Bose, F., Ayral, A., Albouy, P.A., Datas, L. and Guizard, C. (2004) Mesostructure of anatase thin films prepared by mesophase templating. Chemistry of Materials, 16 (11), 2208-2214. 

Liquid-crystalline 3,4-disubstituted furoxans such as 464 (R = 4-alkoxy-benzoyl, Ph) have been prepared by cyclodimerization of 4-ACOC6H4CNO, followed by hydrolysis to 464 (R = H) and acylation. The products form a nematic mesophase (537). 

R. Hermes and K. H. Bauer. Preparation and characterization of amphiphilic membranes with lyotropic mesophases for simulation of skin permeation resistance. Pharmazie 50 481-486 (1995). 

Investigators of cellulosic liquid crystals have two main motivations to study mesophase formation primarily from a scientific viewpoint or a technolomcsd vie oint. The main focus of the latter has been on the potential of preparing high strength/high modulus regenerated cellulose fibers. Another potentim use of cellulosic liquid crystal derivatives is as chiroptical filters (S,lfi). 

Advances in the chemistry of [M(CN)5L]" complexes, for M = Fe, Ru, and Os, have been reviewed.There has been rather little activity in the preparation of novel complexes, but considerable activity in studying the properties, especially solvatochromism and various aspects of kinetics of substitution, of known complexes. However there has been an attempted preparation of [Fe(CN)5(Ci2H25NH2)], in the hope of generating micelles or lyotropic liquid crystals. This preparation appeared to yield [Fe(CN)4(H20)(Ci2H25NH2)], whose alkali metal salts gave a hexagonal mesophase in water, but were also readily hydrolyzed to [Fe(CN)4(H20)2] . Heterobinuclear complexes of the form [(NC)5FeL ML 5] " " have been much studied, especially in relation to intramolecular electron transfer (see Section 5.4.2.2.5). 

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