Morphological changes of gel-type functional polymers after intermatrix synthesis of polymer stabilized silver nanoparticles

This paper reports the results of intermatrix synthesis (IMS) of silver metal nanoparticles (Ag-MNPs) in Purolite C100E sulfonic ion exchange polymer of the gel-type structure. It has been shown that the surface morphology of the initial MNP-free polymer is absolutely smooth, but it dramatically changes after the kinetic loading of Ag on the polymer and then IMS of Ag-MNPs. These morphological changes can be explained by the interaction of Ag-NPs with the polymer chains, leading to a sort of additional cross-linking of the polymer. As a result, the modification of the gel-type matrix with Ag-MNPs leads to the increase of the matrix cross-linking, which results in the increase of its surface area and the appearance of nanoporosity in the polymer gel. Ag-MNPs are located near the polymer surface and do not form any visible agglomerations. All these features of the nanocomposites obtained are important for their practical applications in catalysis, sensor applications, and bactericide water treatment.     

Nanofluidic delivery of molecules: integrated plasmonic sensing with nanoholes

This article presents the detailed analysis of nanofluidics as a mechanism for the delivery of residual vapour/gas molecules in the air to nanoscale apertures in a porous metal or composite membrane with surface plasmons producing field hotspots near the apertures. Finite element analysis is used to calculate and to optimise the flow rate of air through apertures of different diameters with partial slip boundary conditions. Comparison of the calculated nanofluidic delivery rates with those due to diffusion of the tested residual molecules in the air is also conducted. Typical structural and material parameters at which either of these delivery mechanisms appears dominant are determined. Ways for further optimisation and enhancement of the operational capabilities of the described structures as nano-optical sensors and measurement techniques are also identified and discussed.     

Stress transfer in polyacrylonitrile/carbon nanotube composite fibers

Gel spun polyacrylonitrile/carbon nanotube (PAN/CNT) composite fibers have been produced, and the stress-induced G′ Raman band shifts in the CNTs have been monitored to observe stress transfer during fiber strain. Improvements in CNT quality, CNT dispersion, and post-processing fiber drawing are shown to increase the stress transfer from the matrix to the CNT. Radial breathing mode (RBM) intensity of specific CNT chiralities confirms CNT debundling during fiber processing. During PAN/CNT fiber straining, there reaches a plateau in the CNT G′ downshift, signifying that the stress on the CNT is maintained despite continued straining of the PAN/CNT fiber. Correlating CNT strain with CNT modulus and volume fraction allows for the interfacial shear strength (τ_i) of the PAN-CNT interface to be determined. The as-spun and fully drawn PAN/CNT-A (99/1) nano composite fibers exhibit τ_i of 13.1 and 30.9 MPa, respectively, while an improved CNT dispersion (PAN/CNT-A (99.9/0.1)) results in τ_i equal to 44.3 MPa.     

Surface characterization and direct bioelectrocatalysis of multicopper oxidases

Multicopper oxidases (MCO) have been extensively studied as oxygen reduction catalysts for cathodic reactions in biofuel cells. Theoretically, direct electron transfer between an enzyme and electrode offers optimal energy conversion efficiency providing that the enzyme/electrode interface can be engineered to establish efficient electrical communication. In this study, the direct bioelectrocatalysis of three MCO (Laccase from Trametes versicolor, bilirubin oxidase (BOD) from the fungi Myrothecium verrucaria and ascorbate oxidase (AOx) from Cucurbita sp.) was investigated and compared as oxygen reduction catalysts. Protein film voltammetry and electrochemical characterization of the MCO electrodes showed that DET had been successfully established in all cases. Atomic force microscopy imaging and force measurements indicated that enzyme was immobilized as a monolayer on the electrode surface. Evidence for three clearly separated anodic and cathodic redox events related to the Type 1 (T1) and the trinculear copper centers (T2, T3) of various MCO was observed. The redox potential of the T1 center was strongly modulated by physiological factors including pH, anaerobic and aerobic conditions and the presence of inhibitors.     

Optical add-drop multiplexers based on the antisymmetric waveguide Bragg grating

A novel optical add-drop multiplexer (OADM) based on a null coupler with an antisymmetric grating was designed and experimentally demonstrated. The antisymmetric grating exclusively produces a reflection with mode conversion in a two-mode waveguide. This improves the performance compared with previous demonstrations that used tilted Bragg gratings. Our design minimizes noise and cross talk produced by reflection without mode conversion. In addition, operational bandwidth and, versatility are improved while the compactness and simplicity of the null coupler OADM are maintained.     

Carbon nanotubes as nanoreactors for fabrication of single-crystalline Mg3N2 nanowires

Due to fast decomposition of Mg3N2 in the presence of water in the atmosphere (Mg3N2+6H2O-->3Mg(OH)2+2NH3), the synthesis of single-crystalline Mg3N2 nanowires has been a challenge. Here, we demonstrate that carbon nanotubes may serve as nanoreactors for a simple thermal reaction process resulting in the first fabrication of high-quality, large-yield, single-crystalline Mg3N2 nanowires. The Mg3N2 nanowires are homogeneously sheathed over their entire lengths with very thin graphitic carbon tubular layers, which effectively prevent their decomposition (even when the samples are put into water or exposed to atmosphere for several months). We have systematically analyzed for the first time the Mg3N2 nanomaterial by means of transmission electron microscopy (TEM), high-resolution TEM, and electron diffraction. Successful fabrication of carbon sheath protected Mg3N2 nanowires may promote further experimental studies on their crystal structures and properties.     

Evidence for long-lived, optically generated quenchers of excitons in single-walled carbon nanotubes

The nonlinear dependence of near-infrared photoluminescence (PL) emission on excitation intensity has been measured for individual nanotubes representing six different (n,m) species. Significant deviations from linearity are observed for intensities as low as ~100 W/cm(2), and an approximate inverse correlation is found between nonlinearity and PL action cross section (brightness). A model in which all PL nonlinearity arises from exciton-exciton annihilation is insufficient to account for the experimental data using realistic parameters. It is proposed that additional nonlinear quenching arises from photoinduced quenching states or species with longer lifetimes than emissive excitons. Evidence is also found for metastable photogenerated PL quenchers with lifetimes up to 20 s.     

Structural Relaxation, Glass Transition, Viscous Formability, and Crystallization of Zr-Cu–Based Bulk Metallic Glasses on Heating

In this article, we summarize our recent findings on relaxation, glass transition, viscous flow, and crystallization of Zr-Cu?Cbased metallic glasses on heating. At least two processes related to the diffusivities of different alloying elements take place in the glass-transition region of a Zr-Cu-Al-Ni glassy alloy. Also, we report an unusual solidification behavior of the bulk glassy alloy produced using low-purity Zr in which both primary and eutectic-type structural constituents were formed simultaneously during solidification of the melt. In addition, viscous flow and structure changes in the Zr-Cu-Al-Ag glassy alloy are examined in both the glass-transition and supercooled liquid regions. This alloy is found to exhibit localized phase separation leading to nanocrystallization before massive crystallization of the entire sample.