Advanced Materials Research Vols. 1120-1121

Abstract: In a redox system containing ascorbic acid(AA) and ammonium persulfate(APS), Poly(o-chloroaniline)(POC) micro/nanostructures including nanoparticles, nanofibers, and microspheres were successfully prepared through a self-assembly process in absence of additional template. The results indicated that POC morphologies were strongly affected by the molar ratio of o-chloroaniline(OC) to ascorbic acid([OC]/[AA]) and the reaction temperature. The fibrillar or spherical POC micro/nanostructures could be dynamically controlled in the AA/APS redox system by changing the polymerization rate of OC monomers. Thermogravimetric analysis showed that the POC nanofibers had a better thermal stability than POC microspheres. The conductivity of POC nanofibers could reach 5.5×10^-3S/cm, while the microspheres were almost insulators.

Abstract: Functional Polyaniline (PANI) nanotubes are easily synthesized in high yield by an in situ polymerization using a fibrillar complex of acid orange II (AO II) and FeCl₃ as a template. During the process, the complex templates help direct the growth of fibrillar PANI on their surfaces, resulting in the formation of composite micro/nanofibers of PANI. After polymerization, by the post-treatment of removing templates in 1.0 M hydrochloric acid solution, PANI nanotubes with azo function and high electric conductivity of PANI are readily fabricated. The PANI nanotubes have about 150nm-300nm in diameter and several microns in length. At room temperature, the electric conductivity of PANI nanotubes is up to 10^-1 S/cm order of magnitude. The characterizations, including FTIR, UV-visible, XRD and TG, are presented.

Abstract: Submicron hybrid particles were prepared by direct polymerization of three monomers of styrene, methyl methacrylate (MMA), and vinyl acetate (VAC) onto the hydrophilic surface of 230 nm silica submicron particles without any coupling agent in a semi-continuous emulsifier-free emulsion polymerization at a monomer starved condition. The polymerization was initiated by potassium persulfate with constant monomer feed at 0.01, 0.02, or 0.04 mL/min, after adding 230 nm silica seed particles. The particle growth was investigated with a laser particle size analyzer and SEM, and the particle surfaces by Fourier transform infrared spectroscopy (FT-IR). It was founded that the growth of the hybrid particles depended on the hydrophobic characteristics of the polymers. When monomer was the most hydrophobic styrene, polystyrene (PS) shells split off from the hydrophilic surface of the unmodified silica particle whenever the shells reached a limit of ~20 nm. However, both polymethyl methacrylate (PMMA) and polyvinyl acetate (PVAC) shells grew constantly on the hydrophilic surface of silica particles. In the process of the whole reaction, the SiO₂/PMMA and SiO₂/PVAC hybrid particles kept almost monodisperse.

Abstract: Hybrid nanoparticles were prepared by direct polymerization of methyl methacrylate, vinyl acetate, and styrene monomers onto the unmodified hydrophilic surfaces of 33 nm silica nanoparticles in a semi-continuous soap-free emulsion polymerization at a monomer starved condition. The polymerization was initiated by potassium persulfate with constant monomer feed at 0.01, 0.02, or 0.04 mL/min. The growth of the core-shell nanoparticles were measured by a laser particle size analyzer. FT-IR spectra analysis confirmed the hybrid structures of the synthesized nanoparticles. SEM images and size exclusion chromatography (SEC) results indicated regular core-shell microsphere structures. The hybrid nanoparticles increased in monodispersity and size over 100 nm with the reaction. However, SiO₂/polystyrene (PS) nanoparticles grew much faster compared with SiO₂/polymethyl methacrylate (PMMA) and SiO₂/polyvinyl acetate (PVAC). There was particle coagulation, about 12 SiO₂/PS particles aggregating to one, in the early stage of the seeded process. In addition, PS secondary particles were formed before the particle coagulation, and then merged with the SiO₂/PS nanoparticles in the particle coagulation. The formation of SiO₂/polymer hybrid nanoparticles depended on the hydrophilic characteristics of the polymer, and the size of silica seeds.

Abstract: A new process has been developed to obtain high density nanocrystalline diamond (NCD) film via a double bias voltage hot filament-assisted plasma enhanced chemical vapor deposition (HF-PECVD). The microstructure and characterization of the film were analysed by SEM, Raman and AFM. The results show that the NCD film has higher nucleation density and smooth surface, the nanocrysatalline size was in diameter of about 40 nm. Three Raman band near 1150m^-1, 1330 cm^-1 and 1590m^-1 lie in the specrum. The growth mechanism of naocrystalline diamond film was analysized at last.

Abstract: The paper studied the effect of n-LaB₄O₇ additives of different contents on tribological behaviors of the ion nitrocarburized layer at higher temperature. It is found that 7% n-LaB₄O₇ additives can improve obviously the tribological performances of the ion nitrocarburized layer. This because that synergetic effect of friction reduction and wear resistance is produced between the n-LaB₄O₇ additives and ion nitrocarburized layer under higher temperature, load and frequence, and the solid lubrication films including oxide, nitride and sulphate and so on are formed on the friction surface to separate the contact between the metal sufaces, and furthermore the n-LaB₄O₇ particles on the friction surface play the "Micron nanobearing" function, which make the ion nitrocarburized layer have the more excellent tribological performances.

Abstract: The paper studied the effect of n-Na₂B₄O₇ additives of different content on tribological performances of the ion nitrocarburized layer. It is found that 7% n-Na₂B₄O₇ additive can improve greatly the friction reduction and wear resistance of the ion nitrocarburized layer under different conditions. This because that synergetic effect of friction reduction and wear resistance is produced between n-Na₂B₄O₇ additive and ion nitrocarburized layer under higher temperature, frequence and load, and the chemical reaction films including oxide, nitride, BN, and sulphide and so on formed on the friction surface play the solid lubrication function, and the n-Na₂B₄O₇ particles on the friction surface play the "Micron nanobearing" function, translating the sliding friction into the rolling friction, which can make the ion nitrocarburized layer possess the excellent tribological performances.

Abstract: W@SiO₂ shielding composite microspheres were prepared by Sol-gel method for the first time. The component and morphology were investigated by Fourier transform infrared (FT-IR) spectra, Transmission electron microscopy (TEM) and Energy dispersive X-ray spectroscopy (EDX). The results reveal that polyvinylpyrrolidone (PVP) was introduced to the surface of tungsten nanoparticle successfully, and tungsten nanoparticle had been coated with silica. The appropriate hydrolysis reaction time is 3h, core-shell structure W@SiO₂ shielding composite microsphere can be synthesized and free silica decrease sharply. Core element and shell element of W@SiO₂ shielding composite microspheres were proved to be tungsten and silica respectively.

Abstract: The influence of different factors in the alcogel preparation process and ambient pressure drying process on packing density of hydrophobic TiO₂ aerogel synthesized by ambient pressure drying (APD) and the optimum preparation conditions were investigated by the orthogonal test with four-factor and three-level L₉(3⁴), respectively. The morphology and structural properties of hydrophobic TiO₂ aerogels with different density were characterized by Fourier Transform Infrared Spectroscopy (FT-IR), Thermogravimetry (TG), N₂ adsorption-desorption measurement and Scanning Electron Microscope (SEM). The results showed that the most important factors in the preparation process for TiO₂ aerogels with low-density under ambient pressure are aging time, the volume ratio of C₂H₅OH to TBT, ethanol immersion time and hydrophobic modification time. The optimized preparation conditions are that aging time is 24 h, the volume ratio of C₂H₅OH to TBT is (7+7) : 5, the volume ratio of H₂O to TBT is 1.7 : 5, the volume ratio of HAc to TBT is 1.7 : 5, ethanol immersion time is 24 h, hydrophobic modification time is 48 h, hexane solvent replacement time is 24 h and the drying temperature is 393 K. TiO₂ aerogels with density of 460 kg/m³ was obtained at the optimized conditions. TiO₂ aerogel with lower density displays higher specific surface area, porosity and pore volume as well as the larger pore size.

Abstract: An efficient method of preparing nanostarch using high-intensity ultrasonic irradiation and acid hydrolysis was discussed. The transmission electron microscope (TEM) showed that the nanosized starch particles were in shape of sphere with the size of 80-120 nm, and their surfaces were rough with many flocci. The Fourier transform infrared spectrometer (FT-IR) revealed that the products maintained the original biological characteristics, and the molecules did not undergo any chemical changes. In addition, the effects of experimental conditions were analyzed and a plausible mechanism was proposed to explain the formation of the nanostarch.