Multiwalled carbon nanotubes (MWNTs)/nylon-6 (PA6) nanocomposites with different MWNTs loadings have been prepared by the simple melt-compounding approach. A fine and homogeneous dispersion of MWNTs throughout PA6 matrix is observed by transmission electron microscopy. Scanning electron microscopy observation on the fracture surfaces of the composites shows not only a uniform dispersion of MWNTs but also a strong interfacial adhesion with the matrix, as evidenced by the presence of many broken but strongly embedded carbon nanotubes (CNTs) in the matrix and by the absence of debonding of CNTs from the matrix. Beadlike morphology is also observed along the stretched CNTs and their bundles, probably indicating the anchoring locations of the CNTs defects (within the beads) along the tubes where the PA6 matrix has strong interfacial interactions with the CNTs, thus being favorable to stress transfer from polymer to CNTs. Mechanical testing (by tensile and nanoindentation tests as well as dynamic mechanical analysis) shows that, compared with neat PA6, the elastic modulus and the yield strength of the composite are greatly improved by about 214% and 162%, respectively, with incorporating only 2 wt % MWNTs. In addition, a unique crystallization and melting behavior of MWNTs/PA6 composites are observed and discussed by combining differential scanning calorimetry and X-ray diffraction; that is, only the α-form crystals are observed in MWNTs/PA6 composites, which is quite different from the case observed in PA6/clay nanocomposites.

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Nanoporous gold with networks of interconnected ligaments and highly porous structure holds stimulating technological implications in fuel cell catalysis. Current syntheses of nanoporous gold mainly revolve around de-alloying approaches that are generally limited by stringent and harsh multistep protocols. Here we develop a one-step solution phase synthesis of zero-dimensional hollow nanoporous gold nanoparticles with tunable particle size (150-1,000 nm) and ligament thickness (21-54 nm). With faster mass diffusivity, excellent specific electroactive surface area and large density of highly active surface sites, our zero-dimensional nanoporous gold nanoparticles exhibit ~1.4 times enhanced catalytic activity and improved tolerance towards carbonaceous species, demonstrating their superiority over conventional nanoporous gold sheets. Detailed mechanistic study also reveals the crucial heteroepitaxial growth of gold on the surface of silver chloride templates, implying that our synthetic protocol is generic and may be extended to the synthesis of other nanoporous metals via different templates.

We present the next generation covert plasmonic security labels based on Ag nanowire structures and their polarization dependent surface-enhanced Raman scattering (SERS) imaging. The security labels consist of Ag nanowires fabricated by two-photon lithography and thermal evaporation, where molecular probes of choice are deposited. Simulation and experimental results show that the SERS signals from the embedded molecules depend significantly on the polarization of the incident field. The covert molecular information cannot be revealed directly from the physical features, but can only be read-out selectively by polarization-dependent SERS imaging. Our plasmonic security labels exhibit very narrow spectral fingerprint vibration, which is more specific than broadband colorimetry-based systems. The polarization-dependent SERS intensity, molecular fingerprint of SERS spectra, and versatile geometrical design by two-photon lithography have made our plasmonic Ag nanowire structures an ideal candidate as advanced security solutions for anti-counterfeiting application.

Most of the surface-enhanced Raman scattering (SERS) substrates are 2D planar systems, which limits the SERS active area to a single Cartesian plane. Here, we fabricate 3D SERS substrates with the aim to break the traditional 2D SERS active area limitation, and to extend the SERS hotspots into the third dimension along the z-axis. Our 3D SERS substrates are tailored with increased SERS hotspots in the z-direction from tens of nanometers to tens of micrometers, increasing the hotspots in the z-direction by at least an order of magnitude larger than the confocal volume (~1 μm) of most Raman spectrometers. Various hierarchical 3D SERS-active microstructures are fabricated by combining 3D laser photolithography with Langmuir-Blodgett nanoparticle assembly. 3D laser photolithography creates microstructured platforms required to extend the SERS-active area into 3D, and the self-assembly of Ag nanoparticles ensures homogeneous coating of SERS-active Ag nanoparticles over the entire microstructured platforms. Large-area 3D Raman imaging demonstrates that homogeneous signals can be collected throughout the entire 3D SERS substrates. We vary the morphology, height, and inclination angles of the 3D microstructures, where the inclination angle is found to exhibit strong influence on the SERS signals. We also demonstrate a potential application of this hierarchical 3D SERS substrate in information tagging, storage and encryption as SERS micro-barcodes, where multiple micro-barcodes can be created within a single set of microstructures.

The crystal transformation and thermomechanical properties of melt‐intercalated poly(vinylidene fluoride) (PVDF)/clay nanocomposites are reported in this study. Thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) were used to study the thermal properties of PVDF and its nanocomposites with various clay concentrations. The incorporation of clay in PVDF results in the formation of β‐form crystals of PVDF. DSC study of melting behavior suggested the presence of only α‐phase crystals in neat PVDF and both α‐ and β‐phase crystals in the nanocomposite. This conclusion was corroborated by findings from Fourier‐transform infrared (FTIR) spectroscopy and X‐ray diffraction (XRD). Dynamic mechanical analysis (DMA) indicated significant improvements in storage modulus over a temperature range of 20–150 °C. The coefficient of thermal expansion (CTE) decreases with increasing clay loading. Copyright © 2004 Society of Chemical Industry

The crystallization and melting behavior of neat nylon-6 (PA6) and multi-walled carbon nanotubes (MWNTs)/PA6 composites prepared by simple melt-compounding was comparatively studied. Differential scanning calorimetry (DSC) results show two crystallization exotherms (T CC,1 and T CC,2 ) for PA6/MWNTs composites instead of a single exotherm (T CC,1 ) for the neat matrix. The formation of the higher-temperature exotherm T CC,2 is closely related to the addition of MWNTs. X-ray diffraction (XRD) results indicate that only the α-phase crystalline structure is formed upon incorporating MWNTs into PA6 matrix, independently of the cooling rate and annealing conditions. These observations are significantly different from those for PA6 matrix, where the increase in cooling rate or decrease in annealing temperature results in the crystal transformation from α-phase to γ -phase. The crystallization behavior of PA6/MWNTs composites is also significantly different from those reported in PA6/nanoclay systems, probably due to the difference in nanofiller geometry between one-dimensional MWNTs and twodimensional nanoclay platelets. The nucleation sites provided by carbon nanotubes seem to be favorable to the formation of thermodynamically stable α-phase crystals of PA6. The dominant α-phase crystals in PA6/MWNTs composites may play an important role in the remarkable enhancement of mechanical properties.