Enhanced electrical conductivity and hardness of silver-nickel composites by silver-coated multi-walled carbon nanotubes.

We investigated electrical conductivity and Vickers hardness of Ag- and Ni-based composites prepared by powder metallurgy involving spark plasma sintering. The starting composition was Ag:Ni = 61:39 vol%, which provided an electrical conductivity of 3.30 × 10(5) S cm(-1) and a hardness of 1.

Synthesis, structural analysis, and visualization of a library of dendronized polyphenylacetylenes.

A library of eleven high cis-content cis-transoidal polyphenylacetylenes (PPAs) dendronized with self-assembling dendrons was prepared from a library of fifteen convergently synthesized macromonomers. Using [Rh(C triple bond CPh)(nbd)(PPh(3))(2)] (nbd=2,5-norbornadiene) in the presence of 10 equiv of N,N-dimethylaminopyridine, predictive control over molecular weight and narrow molecular weight distribution are obtained. The PPA backbone serves as a helical scaffold for the self-assembling dendrons.

Thermoreversible cis-cisoidal to cis-transoidal isomerization of helical dendronized polyphenylacetylenes.

High cis content (81-99%) cis-transoidal polyphenylacetylene (PPA) jacketed with amphiphilic self-assembling dendrons, poly[(3,4-3,5)mG2-4EBn] with m = 8, 10, 12, 14, 16, and (S)-3,7-dimethyloctyl, were synthesized by Rh(C triple bond CPh)(nbd)(PPh(3))(2) (nbd = 2,5-norbornadiene)/N,N-(dimethylamino)pyridine (DMAP) catalyzed polymerization of macromonomers. The resulting cylindrical PPAs self-organize into hexagonal columnar lattices with intracolumnar order (Phi(h)(io)) and without (Phi(h)). The polymers with m = 12, 14, and 16 exhibit also a hexagonal columnar crystal phase (Phi(h,k)).

Designing libraries of first generation AB3 and AB2 self-assembling dendrons via the primary structure generated from combinations of (AB)(y)-AB3 and (AB)(y)-AB2 building blocks.

Structural analysis of three libraries of up to five generations of self-assembling dendrons based on AB(3), AB(2), and combinations of AB(3) with AB(2) building blocks (Percec et al. J. Am.

Grazing-incidence x-ray diffraction study of Langmuir films of amphiphilic monodendrons.

We have used pressure-area isotherms and grazing-incidence x-ray diffraction to study structures of Langmuir films of first-generation monodendrons with two or three peripheral alkyl chains. Unlike the structures observed in their bulk liquid crystalline mesophases, these multichain monodendrons form either a centered rectangular lattice with molecular axes tilted toward nearest neighbors or an oblique lattice with molecular axes tilted in low-symmetry directions.

Giant supramolecular liquid crystal lattice.

Self-organized supramolecular organic nanostructures have potential applications that include molecular electronics, photonics, and precursors for nanoporous catalysts. Accordingly, understanding how self-assembly is controlled by molecular architecture will enable the design of increasingly complex structures. We report a liquid crystal (LC) phase with a tetragonal three-dimensional unit cell containing 30 globular supramolecular dendrimers, each of which is self-assembled from 12 dendron (tree-like) molecules, for the compounds described here.

Synthesis and NaOTf mediated self-assembly of monodendritic crown ethers.

The synthesis of ten benzyl ether based self-assembling monodendrons containing benzo[15]crown-5 at their focal point is presented. These dendritic building blocks self-assemble either directly or via complexation with NaOTf in two-dimensional smectic B, smectic A, and p6mm hexagonal columnar (Phi(h)) and three-dimensional Pm3n cubic lattices. Retrostructural analysis of these lattices and of the lattices generated from the same monodendrons containing various other functional groups at their focal point by X-ray diffraction experiments provided for the first time a correlation between the molecular structure and the shape of the monodendron, the shape of the supramolecular dendrimer and the symmetry of the lattice.

Plastic- and liquid-crystalline architectures from dendritic receptor molecules.

Host molecules with U-shaped receptor cavities have been derivatized at their convex side with two n-hydrocarbon tails (1), two first-generation (2), and two second-generation (3) monodendritic hydrocarbon tails. Although hosts 1 and 2 display plastic-crystalline behavior, evidence suggests that host 3 forms a cubic liquid-crystalline phase. In this phase, molecules of 3 are arranged in spherical supramacromolecular assemblies, in which the receptor cavities are situated in the core and the hydrocarbon tails at the periphery.

Exploring and expanding the three-dimensional structural diversity of supramolecular dendrimers with the aid of libraries of alkali metals of their AB(3) minidendritic carboxylates.

The synthesis of the alkali metal salts of 3,4,5-tris(n-alkan-1-yloxy)benzoic acid [(3,4,5)nG1-CO(2)M, where n is the number of methylenic units in the alkane group for n=12, 14, 16, 18 and M=Li, Na, K, Rb, Cs] is described. The structural analysis of these AB(3) molecules by a combination of methods which includes X-ray diffraction experiments was performed. These experiments have demonstrated that (3,4,5)nG1-CO(2)M self-assemble at low temperatures into supramolecular cylinders and at high temperatures into spheres which subsequently self-organize into two-dimensional c2mm rectangular columnar, p6mm hexagonal columnar, three-dimensional Pm(-)3n and Im(-)3m cubic lattices.