5.1. Nanoalloys of Group 11 (Cu, Ag, Au) 865 5.1.1. Cu−Ag 866 5.1.2. Cu−Au 867 5.1.3. Ag−Au 870 5.1.4. Cu−Ag−Au 872 5.2. Nanoalloys of Group 10 (Ni, Pd, Pt) 872 5.2.1. Ni−Pd 872 * To whom correspondence should be addressed. Phone: +39010 3536214. Fax:+39010 311066. E-mail: ferrando@fisica.unige.it. † Universita di Genova. ‡ Argonne National Laboratory. § University of Birmingham. | As of October 1, 2007, Chemical Sciences and Engineering Division. Volume 108, Number 3

Nanoalloys: From Theory to Applications of Alloy Clusters and Nanoparticles

Natural fiber reinforced polymer composites (NFPCs) provide the customers with more alternatives in the material market due to their unique advantages. Poor fiber–matrix interfacial adhesion may, however, negatively affect the physical and mechanical properties of the resulting composites due to the surface incompatibility between hydrophilic natural fibers and non-polar polymers (thermoplastics and thermosets). A variety of silanes (mostly trialkoxysilanes) have been applied as coupling agents in the NFPCs to promote interfacial adhesion and improve the properties of composites. This paper reviews the recent progress in using silane coupling agents for NFPCs, summarizes the effective silane structures from the silane family, clarifies the interaction mechanisms between natural fibers and polymer matrices, and presents the effects of silane treatments on the mechanical and outdoor performance of the resulting composites.

Silane coupling agents used for natural fiber/polymer composites: A review

Fourier transform pulsed-gradient spin-echo studies of molecular diffusion

Achieving mastery over the synthesis of metal nanocrystals has emerged as one of the foremost scientific endeavors in recent years. This intense interest stems from the fact that the composition, size, and shape of nanocrystals not only define their overall physicochemical properties but also determine their effectiveness in technologically important applications. Our aim is to present a comprehensive review of recent research activities on bimetallic nanocrystals. We begin with a brief introduction to the architectural diversity of bimetallic nanocrystals, followed by discussion of the various synthetic techniques necessary for controlling the elemental ratio and spatial arrangement. We have selected key examples from the literature that exemplify critical concepts and place a special emphasis on mechanistic understanding. We then discuss the composition-dependent properties of bimetallic nanocrystals in terms of catalysis, optics, and magnetism and conclude the Review by highlighting applications that h...

Bimetallic Nanocrystals: Syntheses, Properties, and Applications

Understanding the contributions of soil microorganisms to soil stabilization at the molecular level will lead to ways to enhance inputs for sustainable agricultural systems. Recent discoveries of copious production of glycoprotein (glomalin) by arbuscular mycorrhizal (AM) fungi and the apparent recalcitrance of this material in soils led to the comparison between concentration of glomalin and aggregate stability. Stability was measured on air-dried aggregates rewetted by capillary action and then subjected to wet sieving for 10 min. Thirty-seven samples from four geographic areas of the U.S. and one area of Scotland were tested. The monoclonal antibody used to discover glomalin on AM hyphae was employed to assess immunoreactive glomalin on aggregate surfaces by immunofluorescence and in extracts from aggregates by enzyme-linked immunosorbent assay (ELISA). Immunofluorescence was observed on at least some surfaces of aggregates from all soils examined, but was most evident on aggregates with high glomalin concentrations. Easily extractable glomalin (EEG) was solubilized by 20 mM citrate, pH 7.0 at 121 °C for 30 min, and total glomalin (TG) was solubilized with 50 mM citrate, pH 8.0 at 121 °C for 90 to 450 min. Some soils required up to seven sequential extractions to remove all of the glomalin. Aggregate stability was linearly correlated (p < 0.001) with all measures of glomalin (mg/g of aggregates) in these soils. The best predictor of aggregate stability (AS) was immunoreactive easily extractable glomalin (IREEG) according to the following relationship: AS = 42.7 +61.3 × log10 IREEG (r2 = 0.86; p <0.001, n = 37).

A survey of soils for aggregate stability and glomalin, a glycoprotein produced by hyphae of arbuscular mycorrhizal fungi

Composite materials consisting of polyaniline nanofibers decorated with noble-metal (Ag or Au) nanoparticles were synthesized with γ radiolysis. Aqueous solutions of aniline, a free-radical oxidant, and/or a metal salt were irradiated with γ rays. Exposure of the solutions to γ rays caused aniline to polymerize as very-thin fibers. Metal particles were also formed during irradiation and decorated the fibers. The shape and size of the metal particles could be changed from nanometer-sized spheres to micron-sized dendrites by varying the ratio of aniline to the metal precursor. Polyaniline-metal composites were characterized using UV−Vis spectroscopy, infrared spectroscopy (FT-IR), X-ray diffraction (XRD), and transmission electron microscopy (TEM). The electrical conductivity of the composites increased with the loading of metal in the nanocomposites and was up to 50 times greater than that of polyaniline fibers alone.

One-pot Synthesis of Polyaniline-metal Nanocomposites

A templateless method for the synthesis of polyaniline nanofibers and nanorods is reported which is based on gamma irradiation of aqueous solutions of aniline in the presence of an initiator.

Radiolytic synthesis of polyaniline nanofibers: A new templateless pathway

La courbure reglee par une balance entre les forces repulsives du groupe de tete opposees par la repulsion des chaines hydrocarbonees augmentees par penetration d'huile dans les queues du tensioactif, est un facteur determinant fondamental de la structure des microemulsions

Curvature as a determinant of microstructure and microemulsions

: The pulsed-gradient spin-echo (PGSE) NMR technique was used to acquire a broad range of solvent self-diffusion coefficients for the toluene/ polystyrene (MW 270,000) system. Self-diffusion coefficients were determined for samples having polymer weight-fractions ranging from 0.04 to 0.90 over temperature range of 25-115 C. Several different approaches to interpretation of the diffusion data have been considered. The temperature dependence of the data exhibits Arrhenius behavior with energies of activation that increase with concentration from 2.6 to 16.2 kcal/mole. Several theories based on the assumption that the solvent diffusion is slowed by the polymer obstructing its diffusion path are also used to interpret this data. Our results support the hypothesis th the normalized diffusion coefficient is relatively independent of thermodynamic parameters. The data are in qualitative agreement with a standard curve for normalized diffusion coefficients. This approach shows potential as a tool for predicting diffusion rates over a wide concentration range for a variety of polymer solvent systems. The final approach used to interpret this data is that of the free volume theory proposed by Vrentas and Duda. The agreement between the free volume theory and experimental data is improved considerably if two of the needed parameters are adjusted to give optimum fits to the experimental diffusion data.

Self-diffusion of toluene in polystyrene solutions

Modulated differential scanning calorimetry was used to probe the thermal behavior of poly(methyl methacrylate) (PMMA) adsorbed onto silica from solution and subsequently dried. Changes in the glass transition were studied as a function of the adsorbed amount and solvent system used to deposit the polymer. The glass transition temperature (Tg) of PMMA was found to increase from 108 °C for the bulk polymer to 136 °C for the polymer adsorbed on silica from toluene (1.0Am). For the polymer adsorbed at approximately half that amount (0.6Am), the glass transition temperature increased to 158 °C. The breadth of the transition also increased from 11 °C for bulk to 61 and 58 °C for the 1.0Am and 0.6Am samples, respectively. When PMMA was adsorbed from a mixed solvent system (5:1 benzene/acetonitrile solution), the transition temperature and its breadth increased even further. For a sample with 0.5Am adsorbed amount from the mixed solvent system, the Tg was increased to 167 °C and the width of the transition was i...

Frank D. Blum

Papers

One-pot Synthesis of Polyaniline-metal Nanocomposites

Radiolytic synthesis of polyaniline nanofibers: A new templateless pathway

Curvature as a determinant of microstructure and microemulsions

Self-diffusion of toluene in polystyrene solutions

Thermal Characterization of PMMA Thin Films Using Modulated Differential Scanning Calorimetry