PREPARATION OF ZINC OXIDE NANOPARTICLE VIA UNIFORM PRECIPITATION METHOD AND ITS SURFACE MODIFICATION BY METHACRYLOXYPROPYLTRIMETHOXYSILANE

Zinc oxide nanoparticles were prepared by uniform precipitation using urea hydrolysis. The ZnO precursor was slowly deposited from aqueous solution. Anionic surfactant was added into solution to block ZnO crystal growth and its agglomeration. Then ZnO nanoparticles were synthesized by the calcination of the precursor at high temperature. Transmission electron microscope (TEM) observation and particle size analyzer demonstrated that the ZnO nanoparticle exhibited nearly spheric shape with 10–40 nm particle size. The surface of the ZnO nanoparticle was modified by methacryloxypropyltrimethoxysilane (MPS). FT-IR (Fourier transform-infrared spectrophotometry) and XPS (X-ray photoelectron spectrophotometry) revealed that MPS was grafted onto the zinc oxide nanoparticle. XRD (X-ray diffraction) showed that the ZnO nanoparticle was a hexagonal crystal with a perfect crystalline structure, and its crystalline morphology was not altered through surface modification. The activation index (AI) of the modified ZnO nanoparticle was measured. It was found that the surface of the ZnO nanoparticle was changed from hydrophilicity into hydrophobicity via surface modification, implying the enhancement of its compatibility with organic polymers. FE-SEM (field scanning electron microscopy) showed that the modified ZnO nanoparticles were homogeneously dispersed in PVC matrices. Consequently, ZnO nanoparticles were integrated with PVC matrices by the grafting organic molecule.     

Fabrication of hydrophobic surface with hierarchical structure on Mg alloy and its corrosion resistance

A hydrotalcite/hydromagnesite conversion coating with hierarchical structure has been fabricated on a Mg alloy substrate by in situ hydrothermal crystallization method. A MgO layer existing between the hydrotalcite/hydromagnesite film and the substrate was formed prior to the hydrotalcite/hydromagnesite film during the crystallization process. After surface treatment with silane coupling agent, the surface of conversion coating changes from hydrophilic to hydrophobic. Scanning electron microscopy (SEM) revealed that the silylated conversion coating with hierarchical structure maintains the original rough surface of which was composed of numerous micro-scale flakes and beautiful flower-like protrusions. Polarization measurements have shown that the hydrophobic conversion coating exhibited a low corrosion current density value of 0.432 μA/cm², which means that the hydrophobic conversion coating can effectively protect Mg alloy from corrosion. Electrochemical impedance spectroscopy (EIS) showed that the impedance of the hydrophobic conversion coating was 9000 Ω. It means that the coating served as a passive layer with high charge transfer resistance.     

Effects of hydrophobicity of the cathode catalyst layer on the performance of a PEM fuel cell

The effects of hydrophobicity of the cathode catalyst layer on the performance of a PEM fuel cell are studied. The surface contact angle is measured to understand the changes of the hydrophobicity of the cathode catalyst layer upon the addition of hydrophobic dimethyl silicone oil (DSO). The results show that the contact angle increases with the DSO loadings in the cathode catalyst layer ranging from 0 to 0.65 mg/cm². The subsequent electrochemical measurements of the fuel cells with various cathodes reveal that the addition of DSO in the cathode catalyst layer can effectively prevent the cathode flooding at high current density, thus leading to a much higher limiting current density and the maximum power density when compared to the fuel cell with a normal cathode. An optimal DSO loading in the cathode catalyst layer is found to be around 0.5 mg/cm² under the testing conditions in this work. The fuel cell with cathode loaded with 0.5 mg/cm² can reach the maximum power density of 356 mW/cm² in H₂/air (or 709 mW/cm² in H₂/O₂) at room temperature, which is around 2.5 times in H₂/air (or 1.8 times in H₂/O₂) of that with normal cathode. All of the results indicate that the hydrophobicity of the cathode catalyst layer plays a crucial role in the water management of the fuel cell. The possible function of the DSO on improved oxygen solubility for the oxygen starved cathode during flooding warrants some further investigation.     

The effect of surface characteristics on the transport of multiple Escherichia coli isolates in large scale columns of quartz sand

Bacteria properties play an important role in the transport of bacteria in groundwater, but their role, especially for longer transport distances (>0.5 m) has not been studied. Thereto, we studied the effects of cell surface hydrophobicity, outer surface potential (OSP), cell sphericity, motility, and Ag43 protein expression on the outer cell surface for a number of E. coli strains, obtained from the environment on their transport behavior in columns of saturated quartz sand of 5 m height in two solutions: demineralized (DI) water and artificial groundwater (AGW). In DI water, sticking efficiencies ranged between 0.1 and 0.4 at the column inlet, and then decreased with transport distance to 0.02-0.2. In AGW, sticking efficiencies were on average 1 log-unit higher than those in DI (water). Bacteria motility and Ag43 expression affected attachment with a (high) statistical significance. In contrast, hydrophobicity, OSP and cell sphericity did not significantly correlate with sticking efficiency. However, for transport distances more than 0.33 m, the correlation between sticking efficiency, Ag43 expression, and motility became insignificant. We concluded that Ag43 and motility played an important role in E. coli attachment to quartz grain surfaces, and that the transport distance dependent sticking efficiency reductions were caused by motility and Ag43 expression variations within a population. The implication of our findings is that less motile bacteria with little or no Ag43 expression may travel longer distances once they enter groundwater environments. In future studies, the possible effect of bacteria surface structures, like fimbriae, pili and surface proteins on bacteria attachment need to be considered more systematically in order to arrive at more meaningful inter-population comparisons of the transport behavior of E. coli strains in aquifers.     

Zinc oxide nanowire enhanced multifunctional coatings for cotton fabrics

Zinc oxide (ZnO) nanowires have been grown on cotton fabric to impart self-cleaning, superhydrophobicity and ultraviolet (UV) blocking properties. ZnO nanowires were grown by the microwave assisted hydrothermal method and subsequently functionalized with steraic acid to obtain a water contact angle of 150°, showing their superhydrophobic nature which is found to be stable up to 4 washings. UV protection of the resulting cotton fabric was also examined and significant decrease in the transmission of UV range was observed. Self-cleaning activity of the ZnO nanowire coated cotton fabric was also studied and it showed considerable degradation of methylene blue under UV light irradiation. These results suggest that ZnO nanowires could form ideal multifunctional coatings for textiles.     

Bis(trifluoromethyl)carbinol polynorbornene as a pseudo-polyelectrolyte in multilayered films

Using weak, opposed to strong polyelectrolytes in multilayer polymer systems provides a convenient means of altering some of the physico-chemical properties of these thin films. Recently, we pushed the limits of the weak polyacids by the introduction of an additional class of polyelectrolytes, the pseudo-polyelectrolytes (pPE). This paper focuses on another pPE, poly[5-(2-trifluoromethyl-1,1,1-trifluoro-2-hydroxypropyl)-2-norbornene] (PNBHFA). As, with poly(4-vinylphenol), multilayer assembly with both a weak and a strong polycation was accomplished from aqueous media. However, this was achieved only at a high pH value of 12.0. The films that were produced were exceptionally thick, > 1.25 μm after only 30 total layers for the poly(allylamine hydrochloride)/PNBHFA system. The films were very hydrophobic with the contact angle of water increasing with the layer number; reaching a maximum of ~ 123° after 50 total layers of poly(diallyldimethylammonium chloride)/PNBHFA.     

Investigation of spreading of surfactant mixtures

Binary surfactant mixtures have been much studied over the years for both great practical and theoretical importance. However, the mechanisms different nonionic surfactant types follow during aggregation into mixed micelles, and probably while forming a mixed surfactant adsorption layer are very poorly understood. Furthermore, the explanation for non-ideal behaviour of trisiloxane surfactant mixtures is still lacking. We have investigated binary mixtures of two commercial superspreaders, Silwet L-77^® and Additive 67^®, with conventional Triton X-100^® surfactant. Observed non-ideal behaviour has been proven to be largely dependent on both total concentration of the binary surfactant mixture and the hydrophobicity of the substrate which it is spreading on. In addition to that, synergistic and antagonistic effects have been revealed and explanations for the observed strange behaviour suggested, with steric problems due to differences in geometry of the surfactant molecules being the key factor. We also showed that present impurities in commercial surfactants can play a major role in the performance of binary surfactant mixtures and that for certain applications mixtures of trisiloxanes with conventional surfactant can be more efficient than trisiloxanes alone.     

复合绝缘子运行状态在线检测技术研究

对复合绝缘子运行状态在线检测技术进行了分类介绍，并探讨了各技术方案的特点与应用概况。     

Effect of adsorption behaviour of polyelectrolytes on fluidity and packing ability of aqueous graphite slurries

The effect of surface hydrophobicity on the adsorption behaviour of polyelectrolytes is investigated using graphite and alumina powder slurries. Graphite slurries containing carboxymethylcellulose (CMC) have a relatively low apparent viscosity and afford a sediment with a relatively high packing fraction as compared to that obtained when using sodium polyacrylate (Na-PAA) as a dispersant, although both have the same functional group. As a greater amount of CMC is adsorbed, it is concluded that its adsorption mechanism involves hydrophobic interaction, thus making it a better dispersant for hydrophobic powders in aqueous media. In contrast, Na-PAA is more effective in dispersing relatively hydrophilic powders such as alumina, as it adsorbs mainly through electrostatic interactions.     

硅橡胶表面分离水珠的局部放电对表面特性的影响

通过对硅橡胶表面存在分离水珠时的局部放电的测量和数据处理，得到了水珠局部放电相位谱图；并采用傅立叶变换红外光谱分析仪(FTIR)分析了局部放电引起的硅橡胶表面结构的变化。水珠间的放电过程中产生的热量和臭氧使硅橡胶表面发生裂解、氧化、交联、水解和缩合等反应，在其表面生产亲水性的硅醇、破坏甲基的对称结构和增加含氧量，这些导致了憎水性能的下降。