分散聚合法包覆无机纳米粒子的研究进展

综述了国内外分散聚合方法包覆无机纳米粒子的研究进展,包括包覆工艺、包覆机理、关键技术及发展趋势。重点分析了聚合温度、引发剂、单体、稳定剂类型和用量、分散介质、无机纳米粒子、包覆时间等因素对包覆效果的影响,结果表明,提高无机纳米粒子和聚合物的亲和性以及无机纳米粒子的分散性是分散聚合包覆无机纳米粒子的关键。     

纳米科学技术进展和前景（Ⅳ）——兼论在化工新材料（含涂料）领域的应用

团聚－分散、吸附－脱附及纳米尺寸单元材料的烧结问题。纳米粒子表面修饰和包覆的研究目的应有明确的应用背景：制备纳米粒子防止粒子长大和解决团聚问题。包覆后的小粒子可以消除粒子表面的带电效应,防止团聚;在粒子表面形成一个势垒,使纳米粒子在制备烧结过程中（若用无机物包覆）,粒子不易长大;若用有机物包覆可使无机纳米粒子能与有机物润湿,若用有机物包覆可使无机纳米粒子能与有机物润湿,用于对塑料改性可以提高强度、韧性、使用温度、防水性等。     

微-纳米无机粒子改性聚丙烯材料的最新进展

综述了近年来微-纳米无机刚性粒子填充改性聚丙烯(PP)材料的最新进展,介绍了微米级、纳米级和微-纳米组合无机刚性粒子的添加对PP复合材料性能的影响。无机刚性粒子越细,越有利于PP材料的增强增韧;无机刚性粒子的表面改性处理对复合材料的微观结构和性能有重要影响。微米无机刚性粒子可提高PP材料的抗冲击强度与刚性,但强度会有所降低;均匀分散的无机纳米粒子同时起到增强增韧的双重作用;具有粒径级的组合粒子的填充改性优于单一无机粒子。     

无机纳米粒子改性聚氨酯弹性体的研究进展

介绍了用无机纳米粒子改性聚氨酯弹性体的制备方法,综述了纳米Si O2、纳米Zn O、纳米蒙脱土、纳米Ca CO3、纳米Ti O2、碳纳米管以及其他无机纳米粒子改性聚氨酯弹性体的研究进展,指出了无机纳米粒子改性聚氨酯弹性体目前存在的问题。     

无机-有机纳米复合乳液的原位聚合及其应用

综述了原位乳液聚合法制备无机．有机纳米复合乳液的技术现状及其形成机理，并运用此技术合成了舍无机纳米粒子的压敏胶用无机-有机纳米复合乳液，分析了纳米粒子在制备过程中的分散性能，从纳米粒子引入方式、乳化剂用量、纳米粒子加入量3方面对压敏胶性能进行考查。     

聚合物无机纳米复合材料的研究进展

介绍了纳米粒子的特性和无机纳米粒子对聚合物改性的机理。总结了聚合物无机纳米复合材料的制备方法。     

纳米粒子直接填充分散法的研究进展

论述了无机纳米粒子的特性及表面处理方法,并介绍了采用纳米粒子直接填充分散法制备高分子基无机纳米复合材料及其应用     

纳米无机粒子在聚合物合金中的选择性分布与迁移机理

概括了决定纳米无机粒子在聚合物共混物中选择性分布的有关因素,强调了聚合物对纳米无机粒子的浸润这一热力学因素和与共混过程有关的动力学因素的影响,并综述了纳米无机粒子迁移的3种可能的机理。     

纳米无机粒子选择性分布与迁移对聚合物共混物形态与性能的影响

综述了纳米无机粒子在聚合物合金中选择性分布的影响因素及纳米无机粒子在聚合物中分散的重要性,重点从相行为、相形态、力学性能、电学性能、流变行为、结晶和熔融行为以及光学性能等方面总结了近年来纳米无机粒子在聚合物共混物中的选择性分布与迁移对以聚合物共混物为基体的纳米复合材料的形态和性能的影响。特别强调了如何利用热力学和动力学因素调控纳米无机粒子在聚合物合金中的分布。     

无机纳米粒子改性硬聚氨酯泡沫塑料的研究进展

介绍了无机纳米粒子改性硬聚氨酯泡沫塑料常用的两种方法和纳米粒子对改性纳米复合材料的力学性能、阻燃性能、导电性能等影响的研究,提出了无机纳米粒子改性硬聚氨酯泡沫塑料存在的问题和未来的研究方向。     

Self-assembly of nanoparticle-rich interphases in fiber reinforced polymeric composites using migrating agents

Thermoplastic additives, known as migrating agents, can be added to nanoparticle loaded thermosetting resins to form self-assembled nanoparticle structures. Most notably, in fiber reinforced thermosetting composites, self-assembled nanoparticle rich fiber-matrix interphases can be formed. While the self-assembly mechanism remains unclear, depletion interaction correctly describes the types of self-assembled structures formed. Formulations containing modest concentrations of migrating agent form self-assembled fiber-matrix interphases without causing aggregation in the bulk. Slight overdoses of migrating agent can lead to the formation of nanoparticle aggregates in the bulk phase, which can ultimately reduce the mechanical properties of the composite. Even larger overdoses of migrating agent cause the formation of large and open nanoparticle aggregates, indicative of rapid aggregation. Depletion theory predicts that larger molecular weight migrating agents should induce greater attractive forces, thus reducing the concentrations required to form these self-assembled structures. In this study, the migrating agent molecular weight dependence on the self-assembly and aggregation phenomenon are investigated. As predicted by depletion theory, larger molecular weights led to the formation of self-assembled interphases and aggregates at lower concentrations.     

Aggregated Nanoparticle Morphology Effects on Membrane Filtration

Nanoparticles are considered potential environmental contaminants because of reported toxicity to biota in the environment. As such, there is interest in understanding how to remove nanoparticles from waters. This study investigated membrane filtration behaviors of 70-nm alumina oxide nanoparticle when aggregated under diffusion limited aggregation and reaction limited aggregation regimes. In this study, nanoparticles were aggregated under conditions of high and low ionic strength to form aggregates of different morphology. Aggregates were filtered using a hydrophilic polyvinylidene fluoride membrane with a pore size of 0.22 µm, 100% nanoparticle removal efficiencies were obtained regardless of aggregation conditions used. Aggregate morphology was quantified by measured fractal dimensions. Fractal structure differences coincided with measured filtration resistance values. Low porosity aggregates provided a filtration resistance 43% greater than high porosity aggregates of the same effective size. Model predictions for measured specific resistance values were improved through incorporation of compressibility indexes. In order to obtain a porous structure with less resistance, a fast coagulation process is suggested for nanoparticle removal.     

Embedded metal nanoparticles as localized heat sources: An alternative processing approach for complex polymeric materials

Metal nanoparticles were utilized as heating elements within nanofibers to demonstrate an alternative approach to thermally process nanostructured polymeric materials. In the photothermal process, resonant light excites the surface plasmon of the nanoparticle and the absorbed energy is converted into heat due to electron-phonon collisions. This heating is efficient and strongly localized, generated from the nanometer-sized metal particles embedded within the polymer. Composite polyethylene oxide (PEO) nanofibers, containing differing concentrations and types of nanoparticles, were fabricated by electrospinning and irradiated by a low intensity laser tuned specifically to the metal nanoparticle surface plasmon absorbance; aggregation of fibers, loss of fibrous structure, and ultimately, complete melting were observed. The photothermal response to irradiation increased with nanoparticle concentration as long as particle aggregation was avoided. Pure PEO nanofibers, or those containing metal nanoparticles possessing a non-resonant surface plasmon, were also irradiated but no melting occurred, demonstrating the controllable specificity of this approach.     

纳米四氧化三铁磁性微粒的表面有机改性

通过液相共沉淀法制备了纳米四氧化三铁溶胶，利用油酸对纳米粒子体进行表面改性和萃取实验，获得油酸包覆的四氧化三铁微粒。采用FT—IR和高分辨透射电镜对改性后的纳米粉体进行结构和形貌的表征。研究结果表明油酸与四氧化三铁纳米粒子间存在化学键结合。油酸对纳米四氧化三铁微粒进行改性，并且对纳米粒子进行包覆，使外表面形成保护层阻止粒子团聚，改性后的四氧化三铁微粒与有机物具有良好的相溶性，采用表面改性显著改善了纳米四氧化三铁微粒的性能指标。     

Graphdiyne as a promising substrate for stabilizing Pt nanoparticle catalyst

At present, Pt nanoparticle catalysts in fuel cells suffer from aggregation and loss of chemical activity. In this work, graphdiyne, which has natural porous structure, was proposed as substrate with high adsorption ability to stabilize Pt nanoparticles. Using multiscale calculations by ab initio method and the ReaxFF potential, geometry optimizations, molecular dynamics simulations, Metropolis Monte Carlo simulations and minimum energy paths calculations were performed to investigate the adsorption energy and the rates of desorption and migration of Pt nanoparticles on graphdiyne and graphene. According to the comparison between graphdiyne and graphene, it was found that the high adsorption ability of graphdiyne can avoid Pt nanoparticle migration and aggregation on substrate. Then, simulations indicated the potential catalytic ability of graphdiyne-Pt-nanoparticle system to the oxygen reduction reaction in fuel cells. In summary, graphdiyne should be an excellent material to replace graphite or amorphous carbon matrix for stabilizing Pt nanoparticle catalysts.     

Nanoparticle generation using corona discharge ions from a supersonic flow in low pressure

From a supersonic flow in a low pressure environment, nanoparticles were generated and the effects of corona discharge ions on the characteristics of the nanoparticles were investigated. The source material was silver, and a corona discharger was used as an ionizer to supply ions to the developed nanoparticle generator. Corona discharge ions provide nanoparticles with a repulsive electrical force that prevents aggregation of the particles. For a detailed analysis of the nanoparticle properties of size, morphology, composition, and charge, nanoparticles were investigated by means of transmission electron microscopy, an X-ray diffraction analysis, energy-dispersive spectroscopy, and by a Faraday cup current measurement. From a numerical calculation approach, the effects of the ions were predicted in terms of the formation and growth of the nanoparticles. Upon application of the corona discharge ions, the mean diameter and standard deviation of the generated nanoparticles were found to decrease. In addition, charged nanoparticles could be generated and the aggregation of particles decreased relatively.     

Dynamic viscosity measurement in non-Newtonian graphite nanofluids

ABSTRACT: : The effective dynamic viscosity was measured in the graphite water-based nanofluids. The shear thinning non-Newtonian behavior is observed in the measurement. On the basis of the best fitting of the experimental data, the viscosity at zero shear rate or at infinite shear rate is determined for each of the fluids. It is found that increases of the particle volume concentration and the holding time period of the nanofluids result in an enhancement of the effective dynamic viscosity. The maximum enhancement of the effective dynamic viscosity at infinite rate of shear is more than 24 times in the nanofluids held for 3 days with the volume concentration of 4% in comparison with the base fluid. A transmission electron microscope is applied to reveal the morphology of aggregated nanoparticles qualitatively. The large and irregular aggregation of the particles is found in the 3-day fluids in the drying samples. The Raman spectra are extended to characterize the D and G peaks of the graphite structure in the nanofluids. The increasing intensity of the D peak indicates the nanoparticle aggregation growing with the higher concentration and the longer holding time of the nanofluids. The experimental results suggest that the increase on effective dynamic viscosity of nanofluids is related to the graphite nanoparticle aggregation in the fluids.     

ZnO Nanofiber and Nanoparticle Synthesized Through Electrospinning and Their Photocatalytic Activity Under Visible Light

In this paper, we fabricate ZnO nanofibers and nanoparticles through electrospinning precursor solution zinc acetate(ZnAc)/cellulose acetate(CA) in mixed-solvent N , N -dimethylformamide/acetone. Depending on the posttreatment of precursor ZnAc/CA composite nanofibers, both ZnO nanofibers and nanoparticles were synthesized after calcination of precursor nanofibers. The morphology and crystal structure of the ZnO nanofiber and nanoparticle were characterized by scanning electron microscopy, transmission electron microscopy, atomic force microscopy, and X-ray diffraction. It was found that the mean diameter of the ZnO nanofiber and nanoparticle was ca. 78 and 30 nm, respectively. The photo-degradation of dye molecules such as Rhodamine B and acid fuchsin catalyzed by the ZnO nanofiber and nanoparticle was evaluated under the irradiation of visible light. Both morphological ZnO species showed strong photocatalytic activity. However, the ZnO nanofiber in the form of nanofibrous mats showed much higher efficiency than the nanoparticle although the latter has a smaller size than the former. The porous structure of ZnO nanofibrous mats is believed to improve the contacting surface areas between the catalyst and the dye molecules, while the aggregation of ZnO nanoparticle in the solution lowers the photocatalytic efficiency.     

丙烯酸丁酯原位悬浮聚合法制备表面改性纳米TiO_2

将悬浮聚合与溶液聚合方法改性纳米TiO2作了对比研究,探讨了介质和单体浓度对结果的影响,并对改性后纳米二氧化钛粒子的分散性能进行了分析。结果表明,在悬浮与溶液聚合条件下,在纳米TiO2粒子表面均能形成聚合物包覆层,当单体浓度为0.25 g/mL时包覆率达最大值。TG表明与以水为介质相比,在乙醇中聚合物包覆率较大,但TEM表明包覆前的纳米粒子在乙醇中更易团聚,因此悬浮聚合条件下更利于聚合物在单个纳米粒子表面的吸附从而促进纳米粒子的分散。     

Effect of the reaction atmosphere on the diameter of single-walled carbon nanotubes produced by chemical vapor deposition

The influence of the reaction atmosphere on the type of single-walled carbon nanotubes (SWNT) grown during chemical vapor deposition (CVD) was investigated. Methane decomposition was catalyzed by Fe/MgO and Fe-Mo/MgO catalysts in argon, nitrogen and their mixtures. Nitrogen influences the carbon species significantly. The aggregation of iron nanoparticles in nitrogen results in the growth of N-doped carbon nanofibers on the Fe/MgO catalyst. A limited iron nanoparticle aggregation in nitrogen occurred on a Fe-Mo/MgO catalyst, on which there was an increase in the diameter of the SWNTs as the reaction atmosphere was more enriched in nitrogen, which was characterized by Raman spectroscopy. These results provide an experimental basis for the rational selection of the reaction atmosphere, and suggest an approach to control the size of the SWNTs in a CVD method.