Guo Qin Xu

Dynamic mechanical behavior of melt-processed multi-walled carbon nanotube/poly(methyl methacrylate) composites

Multi-walled carbon nanotube/poly(methyl methacrylate) composites have been fabricated by melt blending. The nanotubes are well dispersed in the polymer matrix with no apparent damage or breakage. The dynamic mechanical behavior of the composites has been studied. The storage modulus of the polymer is significantly increased by the incorporation of nanotubes particularly at high temperatures.

Decoration of activated carbon nanotubes with copper and nickel

Abstract Activated carbon nanotubes were used as precursors for preparing copper- and nickel-decorated nanotubes. The nature of the activated and decorated nanotubes was studied using high-resolution transmission electron microscopy (TEM) and energy-dispersive X-ray spectroscopy (EDX). The inert surface of oxidized nanotubes was activated by the introduction of catalytic nuclei via a two-step sensitization—activation method and a single-step activation approach. The activated nanotubes catalyze metal deposition specifically onto their surfaces upon immersion in electroless plating baths. Both methods give tubes decorated with nickel. In addition, copper decoration was achieved for the first time. In the two-step sensitization–activation method, the extent of metal decoration was found to be dependent on the age of the sensitizing solution. Densely decorated nanotubes were obtained after three days of sensitizer aging. The single-step activation approach has previously not been applied to carbon nanotube substrates. Our results show that this method is an efficient and simple means of achieving carbon nanotube activation, with the activated tubes showing a high surface coverage of Pd–Sn catalytic nuclei. Electroless plating of such tubes readily results in nanotubes fully coated with nickel and copper.

Broadband optical limiting with multiwalled carbon nanotubes

Optical limiting effects in multiwalled carbon nanotubes have been observed in the visible and infrared spectral regions with nanosecond laser pulses. The multiwalled carbon nanotubes investigated include those suspended in distilled water and embedded in polymethyl methacrylate films. Among all the samples measured, the limiting performance of the carbon nanotube suspension is the best with the limiting threshold determined to be ∼1, 5, and 13 J/cm2 at 532, 700, and 1064 nm, respectively. The possible mechanism for the observed effects is discussed.

LUMINESCENCE CHARACTERISTICS OF IMPURITIES-ACTIVATED ZNS NANOCRYSTALS PREPARED IN MICROEMULSION WITH HYDROTHERMAL TREATMENT

Cu-, Eu-, or Mn-doped ZnS nanocrystalline phosphors were prepared at room temperature using a chemical synthesis method. Transmission electron microscopy observation shows that the size of the ZnS clusters is in the 3–18 nm range. New luminescence characteristics such as strong and stable visible-light emissions with different colors were observed from the doped ZnS nanocrystals at room temperature. These results strongly suggest that impurities, especially transition metals and rare-earth metals-activated ZnS nanoclusters form a new class of luminescent materials.

Poly(vinylidene fluoride)-assisted melt-blending of multi-walled carbon nanotube/poly(methyl methacrylate) composites

Multi-walled carbon nanotubes (MWNTs) were sonicated in the dimethylformamide solution of poly(vinylidene fluoride) (PVDF). The PVDF-covered MWNTs were then melt-blended with poly(methyl methacrylate) (PMMA). The dynamic mechanical behavior of various composites was studied. The presence of a small amount of PVDF leads to a significant improvement in the storage moduli of the MWNT/PMMA composites at low temperatures. The storage modulus of a PVDF/MWNT/PMMA composite containing 0.5 wt.% PVDF is almost twice as that of a MWNT/PMMA composite at 50°C. However, a further increase in the PVDF content leads to a reduction of the storage modulus. The beneficial effect of PVDF diminishes at higher temperatures.

Nonlinear optical properties of some polymer/multi-walled carbon nanotube composites

Abstract Several polymer-coated and polymer-grafted multi-walled carbon nanotubes (MWNTs) were synthesized and characterized using TEM and HRTEM. The polymer-coated or polymer-grafted MWNTs formed stable solutions in DMF. Their nonlinear optical properties were investigated using 532 nm nanosecond laser pulses. These polymer–MWNT composites still possess strong nonlinear optical properties.

Fabrication of highly transparent and conductive indium-tin oxide thin films with a high figure of merit via solution processing.

Deposition technology of transparent conducting oxide (TCO) thin films is critical for high performance of optoelectronic devices. Solution-based fabrication methods can result in substantial cost reduction and enable broad applicability of the TCO thin films. Here we report a simple and highly effective solution process to fabricate indium-tin oxide (ITO) thin films with high uniformity, reproducibility, and scalability. The ITO films are highly transparent (90.2%) and conductive (ρ = 7.2 × 10(-4) Ω·cm) with the highest figure of merit (1.19 × 10(-2) Ω(-1)) among all the solution-processed ITO films reported to date. The high transparency and figure of merit, low sheet resistance (30 Ω/sq), and roughness (1.14 nm) are comparable with the benchmark properties of dc sputtering and can meet the requirements for most practical applications.

Gold nanorods as dual photo-sensitizing and imaging agents for two-photon photodynamic therapy

Gold nanorods with three different aspect ratios were prepared and their dual capabilities for two-photon imaging and two-photon photodynamic therapy have been demonstrated. These gold nanorods exhibit large two-photon absorption action cross-sections, about two orders of magnitude larger than small organic molecules, which makes them suitable for two-photon imaging. They can also effectively generate singlet oxygen under two-photon excitation, significantly higher than traditional photosensitizers such as Rose Bengal and Indocyanine Green. Such high singlet oxygen generation capability under two-photon excitation was ascribed to their large two-photon absorption cross-sections. Polyvinylpyrrolidone (PVP) coated gold nanorods displayed excellent biocompatibility and high cellular uptake efficiency. The two-photon photodynamic therapy effect and two-photon fluorescence imaging properties of PVP coated gold nanorods have been successfully demonstrated on HeLa cells in vitro using fluorescence microscopy and indirect XTT assay method. These gold nanorods thus hold great promise for imaging guided two-photon photodynamic therapy for the treatment of various malignant tumors.

Synthesis of vertically aligned carbon nanotubes on metal deposited quartz plates

Without plasma aid, we have successfully synthesized vertically aligned carbon nanotubes (CNTs) on iron-, cobalt- or nickel-deposited quartz plates by chemical vapor deposition with ethylenediamine as a precursor. The amine serves as both etching reagent for the formation of metal nanoparticles and carbon source for the growth of aligned carbon nanotubes. The carbon nanotubes were vertically aligned in high density on a large area of the plain silica substrates. The density and diameter of CNTs is determined by the thickness of the deposited metal film and the length of the tubes can be controlled by varying the reaction time. High-resolution transmission electron microscopy analysis reveals that the synthesized CNTs are multiwalled with a bamboo-like structure. Energy dispersive X-ray spectra demonstrate that the CNTs are formed as tip growths. Raman spectrum provides definite evidence that the prepared CNTs are multiwalled graphitic structure.

Synthesis and characterization of Eu:Y2O3 nanoparticles

The red-emitting nanophosphor Eu:Y2O3 was synthesized using the the microemulsions method. The microemulsion system was composed of petroleum ether (60-80??C), nonionic surfactants NP5/NP9, aqueous yttrium nitrate/europium nitrate and ammonium hydroxide solution. The nanoparticles were studied by thermal analysis, x-ray diffraction, transmission electronic microscopy, scanning electron microscopy and photoluminescence. The size of the nanoparticles was in the range 10-100?nm, and showed a narrow size distribution, high crystallinity and special luminescent properties. Compared with the phosphors prepared by the conventional method, the quenching concentration of Eu was raised remarkably. For this type of nanophosphor, quenching starts at a Eu concentration of 10% (mol%), while a value of 6-8% was obtained for the conventional one (Tao?Y 1996 Mater. Lett. 28 137-40). Based on this study, we have successfully prepared some promising nanophosphors.