Self-organization of polyaniline during oxidative polymerization: formation of granular structure

The paper is focused on oxidative polymerization of aniline proceeding in an acid medium with a strong oxidant; formation of polyaniline (PANI) granular structures in different steps of the synthesis was studied. The relationship between the processes of self-organization of the growing polymer into supramolecular structures and the steps of molecular synthesis has been revealed. It was shown that during the induction period (the initial synthesis step), insoluble non-conducting products are formed. They are characterized by the absorption band at 430 nm corresponding to the wavelength of the phenazinium cation radical peak. In the second step, the polymer chain growth, conducting PANI granules with the diameter of 50 nm were obtained. These granules consist of spherical particles with the diameter as small as several nanometers. Then, the granule dimensions increased to 200 nm due to the growth of the spheres; the sphere diameter reached 20 nm. The number of spheres in a granule remained constant. Both precipitate and PANI film consist of common structural elements, polymer spheres, organized into granules and larger structures. Suppression of the polymer chain growth leads to the formation of non-conducting aniline oligomers which are self-organized into large particles with fractal structure. To describe the self-organization processes of a growing polymer chain, the diffusion-limited aggregation mechanism was used.     

Self-organization of self-assembled tetrameric porphyrin arrays on surfaces

The incorporation of designed self-assembled supramolecular structures into devices requires deposition onto surfaces with retention of both structure and function. This remains a challenge and can present a significant barrier to developing devices using self-organizing materials. To examine the role of peripheral groups in the self-organization of self-assembled multiporphyrinic arrays on surfaces, Pd(II)-linked square and Pt(II)-linked trapezoidal tetrameric porphyrin arrays with peripheral tert-butylphenyl or dodecyloxyphenyl functionalities were investigated using various spectroscopies and atomic force microscopy. The Pd(II) assembled squares disassemble upon deposition on glass surfaces, while the Pt(II) assembled trapezoids are more robust and can be routinely cast on these surfaces. The orientation and length of the peripheral alkyl substituents influence the resultant structures on surfaces. The tert-butylphenyl-substituted porphyrin array forms discrete columnar stacks, which assemble in a vertical direction via pi-stacking interactions among the macrocycles. The tetrameric porphyrin array with dodecyloxyphenyl groups forms a continuous film via van der Waals interactions among the peripheral hydrocarbon chains. The super-molecules with liquid crystal-forming moieties also form three-dimensional crystalline structures at higher deposition concentrations. These observations clearly demonstrate that the number, position, and nature of the peripheral groups and the supramolecular structure and dynamics, as well as the energetics of interactions with the surface, are of key importance to the two-dimensional and three-dimensional self-organization of assemblies such as porphyrin arrays on surfaces.     

Radical intermediates induced by porphyrin triplets

In the photochemical reactions of triplets of both protoporphyrin-IX-dimethyl-ester (PP) and haematoporphyrin dihydrochloride (HP) with alpha-phenyl-ethyl hydroperoxide (HROOH) in C6H6 at room temperature, both O-O and C-C bonds are broken yielding alkoxy and carbon-centred radicals. The ruptures of C-C and O-H bonds were observed in the photochemical reaction of PP with tert-butanol in the same solvent, yielding alkoxy and carbon-centred radicals at lambda greater than or equal to 366 nm, while HP did not react photochemically with tert-butanol at lambda greater than or equal to 334 nm.     

Polymers with indane units by cationic polymerization

In spite of the difunctionality of the monomers, cationic polymerization of 1,3- and 1,4-diisopropenylbenzene does not lead to branched or cross-linked products. Instead, soluble polymers are obtained, containing the 1,1,3-trimethylindane system as repetitive unit along the backbone. These polymers are interesting materials because of their high glass transition temperature (200°C-250°C) and good thermal stability in air (2% weight loss at 450°C). Although the molar mass of the polyindanes seems to be limited due to a side reaction, it is possible to produce telechelic polyindanes. Substitution of an alkyl side chain onto the isopropenyl groups of 1,4-diisopropenylbenzene leads to monomers which yield substituted polyindanes with glass transition temperatures as low as 26°C. Such polymers still exhibit good thermal stability: at 340°C a weight loss of only 2% occurs. 1,4-Diisopropenylbenzene can even be anionically polymerized to linear polymers. In this case, the resulting polymer possesses isopropenyl phenyl side groups, which can be used as initiators for cationic polymerization of isobutene to obtain grafted copolymers.     

A sol-gel transition induced by dilution

<正>Shaped by multiple noncovalent interactions,the interwoven fibrous network consisting of several components (collagen,laminin and proteoglycans etc.) is a unique feature reserved by the natural extracellular matrix (ECM).Recently,great attention of scientists has been aroused to mimic ECM through constructing the synthetic supramolecular systems[1,2].     

Self-organization of supramolecular complex composed of rigid dendritic porphyrin and fullerene

A second-generation 1,3,5-phenylene-based dendritic porphyrin decorated with flexible alkyl chains exhibited a liquid crystallinity, and the inclusion of fullerene within the nanospace of the dendritic porphyrin strongly affected the mesophase structure in the thermotropic liquid-crystalline phase.     

One-dimensional porphyrin H-aggregates induced by solvent polarity

A series of new porphyrin derivatives possessing the side arms of alkyl-substituted thiophene oligomer were synthesized. The effects of solvent polarity on the formation of supramolecular assembly have been studied by UV-vis absorption, fluorescence emission, and TEM measurement. The linear-shape porphyrin derivatives bearing two thiophene pentamers at meso-position showed the significant spectral changes in both blue-shift and band broadening of Soret bands which indicate the formation of a relatively larger porphyrin H-aggregate that occurred in nonpolar solvent such as n-hexane.     

Polymerization in magnetic field. XVI. Kinetic aspects regarding methyl methacrylate polymerization in high magnetic field

The effect of a high magnetic field of 7 T in the reaction of methyl methacrylate polymerization is emphasized. The intervening magnetokinetic modifications are correlated with the system of radical initiation with benzoyl peroxide, 2,2′‐azobis(2‐methylpropionitrile), 4,4′‐azobis(4‐cyanopentanoic acid), and 1,1′‐azobis(cyclohexane‐1‐carbonitrile). The characterization of the synthesized polymers is correlated with the reaction conditions. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 5678–5686, 2004     

The induced magnetic field in cyclic molecules

The response of a molecule to an applied external magnetic field can be evaluated by a graphical representation of the induced magnetic field. We have applied this technique to four representative, cyclic organic molecules, that is, to aromatic (C(6)H(6), D(6h)), anti-aromatic (C(4)H(4), D(2h)) and non-aromatic (C(4)H(8), D(4h), and C(6)H(12), D(3d)) molecules. The results show that molecules that contain a pi system possess a long-range magnetic response, while the induced magnetic field is short-range for molecules without pi systems. The induced magnetic field of aromatic molecules shields the external field. In contrast, the anti-aromatic molecules increase the applied field inside the ring. Aromatic, anti-aromatic, and non-aromatic molecules can be characterized by the appearance of the magnetic response. We also show that the magnetic response is directly connected to nucleus-independent chemical shifts (NICS).     

Influence of a magnetic field on radicalic polymerization of butyl methacrylate

Butyl methacrylate polymerization, through various procedures, i.e., bulk, solution and emulsion studies in the presence and absence of a magnetic field was studied. The influence of the magnetic field was observed on the development of the reactions, and also on some properties of the synthesized homopolymers. The behavior of the reaction's occurrence, with and without the magnetic field was compared. The homopolymers obtained were characterized from the viewpoint of their stability.     

Direct introduction of heterocyclic units into porphyrin derivatives

In the reaction with quinazoline and 5-phenyl-1,2,4-triazin-5(2H)-one, 5,10,15,20-tetra(4-methoxyphenyl)porphyrin exhibits nucleophilic properties. In quinazoline excess, C—C coupling occurs at the C=N bond of azines and position 3 of the aryl ring to form 5,10,15,20-tetrakis(3-heteryl-4-methoxyphenyl)porphyrins. Monoheteryl-substituted porphyrin was obtained by the reaction of equimolar amounts of 5,10,15,20-tetra(4-methoxyphenyl)porphyrin and 5-phenyl-1,2,4-triazin-5(2H)-one.     

Periodic deformations induced by a magnetic field in planar twisted nematic layers

Magnetic field-induced spatially periodic deformations of planar nematic layers twisted by an angle Φ were investigated numerically. Chiral nematics with pitches compatible with the twist angle and non-chiral nematics twisted by Φ ≤π/2 were considered. Two different modes of deformation, taking the form of stripes, were found: the so called Mode X, with periodicity parallel to the mid-plane director in the undisturbed structure, and Mode Y with periodicity perpendicular to the mid-plane director. The static director distributions were calculated for various magnetic field strengths, twist angles and elastic parameters. The influence of surface tilt was also investigated. Mode X appeared for sufficiently large Φ and was possible in nematics with typical elastic properties. Mode Y appeared provided that the k₂₂/k₁₁ elastic constant ratio and the twist angle Φ were sufficiently small. Both modes arose from the undistorted state when the magnetic field exceeded a threshold value. The spatial period of the patterns increased with field strength. At high field, regions with almost homogeneous deformation arose in the two halves of each stripe. Their width and, simultaneously, the spatial period diverged to infinity at some critical field. This divergence corresponds to the transition to a homogeneously deformed state. Diagrams were constructed showing the ranges of parameters favouring the periodic distortions.     

Periodic deformations induced by a magnetic field in planar twisted nematic layers

Magnetic field-induced spatially periodic deformations of planar nematic layers twisted by an angle Φ were investigated numerically. Chiral nematics with pitches compatible with the twist angle and non-chiral nematics twisted by Φ ? π/2 were considered. Two different modes of deformation, taking the form of stripes, were found: the so called Mode X, with periodicity parallel to the mid-plane director in the undisturbed structure, and Mode Y with periodicity perpendicular to the mid-plane director. The static director distributions were calculated for various magnetic field strengths, twist angles and elastic parameters. The influence of surface tilt was also investigated. Mode X appeared for sufficiently large Φ and was possible in nematics with typical elastic properties. Mode Y appeared provided that the k ₂₂/k ₁₁ elastic constant ratio and the twist angle Φ were sufficiently small. Both modes arose from the undistorted state when the magnetic field exceeded a threshold value. The spatial period of the patterns increased with field strength. At high field, regions with almost homogeneous deformation arose in the two halves of each stripe. Their width and, simultaneously, the spatial period diverged to infinity at some critical field. This divergence corresponds to the transition to a homogeneously deformed state. Diagrams were constructed showing the ranges of parameters favouring the periodic distortions.     

Chaotic transients in surface-stabilized smectic C* cells induced by magnetic field

Recent theoretical developments regarding the understanding of weakly chaotic transients in ferroelectric liquid crystals (FLCs), induced by electric field, are studied in terms of the interaction with magnetic field. Our research is related with the nonlinear dynamical system represented by a thin film of surface-stabilized FLC in smectic C* phase, and subjected by the swinging magnetic field. The computation of the Lyapunov exponents from the dynamic equation for the director field reveals that the director dynamics exhibits limit cycle, hyperchaotic attractor and strange attractor behavior in the dissipative nonlinear media. The transients between director’s phase space trajectories can be handled by the magnetic field parameters. The fundamental understanding of the director dynamics may have a valuable contribution to the applications of thin liquid crystal films.     

Self-organization of a new fluorous porphyrin and C60 films on indium-tin-oxide electrode

The highly fluorinated alkyl moieties of a new porphyrin drive the self-organization of thin films with C(60) on ITO electrodes.     

声场对水合氧化锆凝胶特性的影响

氧化锆具有良好的光学、热学、电学和机械性质[1],氧化锆纳米粉体是制备高性能氧化锆陶瓷的主要材料。溶胶 凝胶法是制备氧化锆纳米粉体的方法之一[2],避免形成硬团聚体是一个关键问题。水合氧化锆干凝胶中非架桥羟基是粉末产生硬团聚体的根源[2]。将超声波应用到溶胶 凝胶过程中可以改变硅凝胶的结构[3],本文对声扬作用下水合氧化锆凝胶的形貌、热特性以及红外吸收光谱等进行分析,研究声场对水合氧化锆凝胶特性的影响,以探讨声场减少硬团聚体形成的机理。1　实验部分1 1　主要仪器日本JEM 100CXII型透射电子显微镜,加速电压200kV;…     

Conformational conversion of DNA G-quadruplex induced by a cationic porphyrin

The interactions between cationic meso-tetrakis(4-(N-methylpyridiumyl))porphyrin (TMPyP4) and the G-quadruplex (G4) of human telomeric single-strand oligonucleotide d(TTAGGG)₂ (S12) have been investigated by means of circular dichroism (CD), UV–visible absorption and fluorescence spectroscopies. It is found that TMPyP4 can preferentially induce the conformational conversion of the G4 structure from the parallel type to the parallel/antiparallel mixture in the presence of K⁺, and that it can directly induce the formation of antiparallel G4 structure from the single-strand oligonucleotide S12 in the absence of K⁺. Furthermore, the comparable experiments of TMPyP4 with two single-strand oligonucleotides S6 d(TTAGGG) and S24 d(TAGGG(TTAGGG)₃T) in the absence of K⁺ show that TMPyP4 can also induce the formation of antiparallel G4 from S24 but not from S6, indicating that the end-loops of the G4 structure are the key factors for the formation of G4 induced by TMPyP4.