Multiscale carbon nanotube-carbon fiber reinforcement for advanced epoxy composites

We report an approach to the development of advanced structural composites based on engineered multiscale carbon nanotube-carbon fiber reinforcement. Electrophoresis was utilized for the selective deposition of multi- and single-walled carbon nanotubes (CNTs) on woven carbon fabric. The CNT-coated carbon fabric panels were subsequently infiltrated with epoxy resin using vacuum-assisted resin transfer molding (VARTM) to fabricate multiscale hybrid composites in which the nanotubes were completely integrated into the fiber bundles and reinforced the matrix-rich regions. The carbon nanotube/carbon fabric/epoxy composites showed approximately 30% enhancement of the interlaminar shear strength as compared to that of carbon fiber/epoxy composites without carbon nanotubes and demonstrate significantly improved out-of-plane electrical conductivity.     

Zur Frage der Vierbindigkeit des Schwefels bei Schwefeldiimiden

Ohne Zusammenfassung

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On the question of the quadrivalence of sulphur in sulphur diimides

     

Band structure of (TMTSF)2X

The electronic structure of the organic conductors (TMTSF)₂X has been explored in terms of the tight binding band structures calculated for a sheet of TSF molecules. The Se 4d-orbitals appear to be critical in enhancing the interstack Se…Se interaction to the point that (TMTSF)₂X becomes pseudo two-dimensional. Based upon the present band structure study, it is discussed whether a normal metallic state or a spin density wave state provides the closed Fermi surface responsible for the Shubnikov-de Haas oscillations observed in (TMTSF)₂PF₆.     

Diels-Alder chemistry of graphite and graphene: graphene as diene and dienophile

The zero-band-gap electronic structure of graphene enables it to function as either the diene or the dienophile in the Diels-Alder reaction, and this versatile synthetic method offers a powerful strategy for the reversible modification of the electronic properties of graphene under very mild conditions.     

Resonance stabilized bis-thiadiazinyl radicals

The resonance stabilized bis-thiadiazinyl framework holds potential as a stable and versatile building block for the design of radical-based conductors and magnetic materials.     

Studies in nuclear magnetic resonance—IX. Rotational barriers in substituted N,N-dimethylbenzamides

The barriers to rotation about the C? N bond in eighteen substituted N,N-dimethylbenzamides have been determined by complete line shape analysis of the NMR spectra of the N,N-dimethyl protons. The barriers have been correlated with the substituent constants σ and σ⁺. It has been shown that polar solvents increase the barrier in N,N-dimethylbenzamide. Acid catalysis of rotation about the amide C? N bond in N-(p-N,N-dimethylcarboxamidobenzyl)-pyridinium bromide has been investigated. ¹⁸O exchange studies show that catalysis is due to N-protonation rather than the formation of a tetrahedral intermediate. The rate of rotation is a function of the Hammett acidity function, H₀, and the water activity, and it is shown that proton exchange between the N- and O-protonated species involves the intermediacy of a water molecule. The differences in chemical shifts for the non-equivalent N, N-dimethyl groups of the benzamides are also a function of the substituents. Possible explanations of this phenomenon are discussed.     

Prototypal dithiazolodithiazolyl radicals: synthesis, structures, and transport properties

New synthetic routes to 1,2,3-dithiazolo-1,2,3-dithiazolylium salts, based on double Herz condensations of N-alkylated 2,6-diaminopyridinium salts with sulfur monochloride, have been developed. The two prototypal 1,2,3-dithiazolo-1,2,3-dithiazolyl radicals HBPMe and HBPEt have been prepared and characterized in solution by cyclic voltammetry and EPR spectroscopy. Measured electrochemical cell potentials and computed (B3LYP/6-31G) gas-phase disproportionation enthalpies favor a low on-site Coulombic repulsion energy U in the solid state. The crystal structures of HBPR (R = Me, Et) have been determined by X-ray crystallography (at 293 K). Both consist of slipped pi-stacks of undimerized radicals, with many close intermolecular S- - -S contacts. Magnetic, conductivity, and optical measurements have been performed and the results interpreted in light of extended Hückel band calculations. The crystalline materials are paramagnetic above 100 K, with room-temperature conductivities sigma(RT) of 10(-5)-10(-6) S cm(-1); the slightly greater conductivity of the R = Et compound can be associated with a more well developed band structure. We suggest a Mott-Hubbard insulator ground state for these materials, with an on-site Coulomb repulsion energy U of about 1.0 eV.