Yeshayahu Talmon

Strong, Light, Multifunctional Fibers of Carbon Nanotubes with Ultrahigh Conductivity

Optimizing Carbon Nanotubes Shorter carbon nanotubes are easier to make, but, when assembled into fibers, the resulting fiber properties are much poorer than might be predicted by theory. Conversely, longer carbon nanotubes have much better properties but are harder to process. Behabtu et al. (p. 182) combined the best of both worlds through scalable wet spinning method, in which they dissolved longer carbon nanotubes and then spun them into fibers that showed excellent strength, stiffness, and thermal conductivity. Exceptional carbon nanotube fibers are produced by a wet spinning process using longer nanotubes as feedstock. Broader applications of carbon nanotubes to real-world problems have largely gone unfulfilled because of difficult material synthesis and laborious processing. We report high-performance multifunctional carbon nanotube (CNT) fibers that combine the specific strength, stiffness, and thermal conductivity of carbon fibers with the specific electrical conductivity of metals. These fibers consist of bulk-grown CNTs and are produced by high-throughput wet spinning, the same process used to produce high-performance industrial fibers. These scalable CNT fibers are positioned for high-value applications, such as aerospace electronics and field emission, and can evolve into engineered materials with broad long-term impact, from consumer electronics to long-range power transmission.

Spontaneous high-concentration dispersions and liquid crystals of graphene

Graphene combines unique electronic properties and surprising quantum effects with outstanding thermal and mechanical properties. Many potential applications, including electronics and nanocomposites, require that graphene be dispersed and processed in a fluid phase. Here, we show that graphite spontaneously exfoliates into single-layer graphene in chlorosulphonic acid, and dissolves at isotropic concentrations as high as approximately 2 mg ml(-1), which is an order of magnitude higher than previously reported values. This occurs without the need for covalent functionalization, surfactant stabilization, or sonication, which can compromise the properties of graphene or reduce flake size. We also report spontaneous formation of liquid-crystalline phases at high concentrations ( approximately 20-30 mg ml(-1)). Transparent, conducting films are produced from these dispersions at 1,000 Omega square(-1) and approximately 80% transparency. High-concentration solutions, both isotropic and liquid crystalline, could be particularly useful for making flexible electronics as well as multifunctional fibres.

Statistical thermodynamics of phase equilibria in microemulsions

The statistical thermodynamics of microemulsions is investigated on the basis of a model which represents microemulsion structure as a random geometry of interspersed oil and water domains generated by a Voronoi tesselation, with the surfactant adsorbed at the boundary. The resulting one‐parameter free energy function predicts two‐ and three‐phase equilibria bearing a strong resemblance to experimental observations on certain alkyl aryl sulfonate–oil–brine microemulsion systems.

Single Nanocrystals of Platinum Prepared by Partial Dissolution of Au-Pt Nanoalloys

Small metal nanoparticles that are also highly crystalline have the potential for showing enhanced catalytic activity. We describe the preparation of single nanocrystals of platinum that are 2 to 3 nanometers in diameter. These particles were generated and immobilized on spherical polyelectrolyte brushes consisting of a polystyrene core (diameter of ∼100 nanometers) onto which long chains of a cationic polyelectrolyte were affixed. In a first step, a nanoalloy of gold and platinum (a solid solution) was generated within the layer of cationic polyelectrolyte chains. In a second step, the gold was slowly and selectively dissolved by cyanide ions in the presence of oxygen. Cryogenic transmission electron microscopy, wide-angle x-ray scattering, and high-resolution transmission electron microscopy showed that the resulting platinum nanoparticles are faceted single crystals that remain embedded in the polyelectrolyte-chain layer. The composite systems of the core particles and the platinum single nanocrystals exhibit an excellent colloidal stability, as well as high catalytic activity in hydrogenation reactions in the aqueous phase.

Vesicle-micelle transition of phosphatidylcholine and octyl glucoside elucidated by cryo-transmission electron microscopy

Vesicle-micelle transition structures of egg phosphatidylcholine (PC) and octyl glucoside (OG) mixtures were observed in the vitrified hydrated state by cryo-transmission electron microscopy (cryo-TEM) and correlated with the macroscopic and molecular changes previously associated with micellization monitored by 90 degrees light scattering and resonance energy transfer between fluorescent lipid probes. Several distinct structural changes occurred as OG was added to the PC vesicles. First, the average vesicle size decreased from 160 nm to less than 66 nm with no apparent change or decrease in optical density (OD). Then, associated with a small rise in OD, samples with open vesicles were observed coexisting with pieces of lamellae and long cylindrical micelles; more micelles were seen at higher [OG]. This mixture of vesicles and cylindrical micelles occurred in the region of the phase diagram previously attributed to vesicle opening, and possibly vesicle size increase. At higher [OG], small spheroidal micelles coexisting with cylindrical micelles correlated with a decrease in OD and changes in the fluorescence signal. At high [OG] when the solution appeared clear, spheroidal micelles were the dominant structure. By using cryo-TEM, a technique which preserves the original microstructure of fluid systems and provides direct images at 1 nm resolution, we have elucidated the vesicle-micelle transition and identified intermediates not known previously in the PC/OG system.

Intermediate structures in the cholate-phosphatidylcholine vesicle-micelle transition

The vesicle-micelle transition of egg phosphatidylcholine (PC) and sodium cholate was described by comparing cryo-transmission electron microscopic (cryo-TEM) images of the structures formed to the associated turbidity changes. These experiments were designed to identify the morphology of the intermediates between vesicles and small spheroidal mixed micelles. With increasing cholate concentration, the vesicular structures changed size and more multilamellar vesicles were seen. Between the apparent upper and lower phase boundaries, three structures were observed: open vesicles, large bilayer sheets (twenty to several hundred nanometers in diameter), and long (150–300 nm) flexible cylindrical micelles. The cylindrical micelles evolved from the edges of the bilayer sheets. At higher relative cholate concentration, the phase boundary was sharply defined by optical clarification of the egg PC-cholate mixtures. Cryo-TEM revealed only small spheroidal mixed micelles at this transition. These results provide the first direct evidence of the structural pathway or of molecular intermediates between a lamellar and a micellar state. Understanding these specific intermediates and the transitions between them is essential to developing reconstitution protocols and properly analyzing either activity or structural data obtained from cholate-dispersed membrane proteins.

Branched Threadlike Micelles in an Aqueous Solution of a Trimeric Surfactant

Very long threadlike micelles observed in aqueous solutions of some surfactants have attracted much attention because of the peculiar rheological properties of these systems. Molecular dynamics simulations have suggested that branched threadlike micelles should exist in concentrated solutions of dimeric surfactants. Here experimental evidence, obtained from transmission electron microscopy at cryogenic temperature, is presented of branched threadlike micelles in aqueous solutions of a triquaternary ammonium (trimeric) surfactant made up of three amphiphilic moieties connected at the level of the head-groups by two propanediyl spacers.

Digital cryogenic transmission electron microscopy: an advanced tool for direct imaging of complex fluids

Abstract Digital imaging cryogenic transmission electron microscopy (cryo-TEM) has become an important extension of TEM at cryogenic temperatures. In this paper, we describe the advantages of the technique and demonstrate its use in the study of two micellar systems. We show how details that were impossible or difficult to image, can be easily observed by this novel technique. We emphasize that the introduction of digital imaging to cryo-TEM is not merely a small technical improvement, but does promise to expand the capabilities of TEM of complex fluids in a most significant way.

Electron diffraction of mollusc shell organic matrices and their relationship to the mineral phase

Abstract Electron diffraction patterns showing orientation of the chitin and protein constituents of the insoluble organic matrix of mollusc shell nacreous layers have been obtained, using low dose conditions and samples cooled to −100°C. Diffraction patterns of the aragonite crystals were also observed. In a gastropod and a bivalve the spatial relationship between the organic matrix constituents and the aragonite crystallographic axes were shown to be the same as was previously observed for a cephalopod using X-ray diffraction, supporting the notion that mineral crystal growth occurs epitaxially upon a matrix template.

Formation of complement-activating particles in aqueous solutions of Taxol: possible role in hypersensitivity reactions

We reported earlier that the anticancer drug paclitaxel (Taxol) activated the complement (C) system in human serum in vitro, raising the possibility that C activation might play a role in the ill-understood hypersensitivity reactions (HSRs) to this drug [J. Natl. Cancer Inst. 90 (1998) 300]. In pursuing the mechanism of C activation by Taxol, the present study provided evidence that dilution of the injection concentrate in aqueous solvents led to the formation of micelles and needle-like structures, both of which caused C activation in vitro. Micelles were formed mainly from Cremophor EL (CrEL), the nonionic emulsifier vehicle of paclitaxel, whose level in Taxol infusion exceeded its critical micelle concentration by at least 400-fold. CrEL micelles were shown by quasi-elastic light scattering and cryo-transmission electron microscopy (cryo-TEM) to be spherical with diameters in the 8-22 nm range; however, de novo formation of 50-300 nm microdroplets following incubation with human plasma suggested further fundamental structural transformation in blood. The needle-like structures extended to the multimicron range and were shown by electron diffraction to be crystalline paclitaxel. Taxol-induced C activation was manifested in varying rises of serum C3a-desarg, iC3b and SC5b-9. The causal role of CrEL micelles in C activation was demonstrated by the fact that filtration of aqueous solutions of Taxol or pure CrEL via 30-kDa cutoff filters eliminated, while the filter retentate restored C activation. C activation by Taxol was also inhibited by 10 mg/ml human immunoglobulin (IVIG). If proven clinically, HSRs to Taxol may represent a hitherto vaguely classified adverse drug reaction recently called C activation-related pseudoallergy (CARPA) [Circulation 99 (1999) 2302].