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固液界面纳米气泡是近十年来表面科学的重要发现之一。从利用原子力显微镜(AFM)在固液界面上观察到纳米气泡以来,科学工作者们已经证实了纳米气泡在固液界面上存在。由于其在微机电系统(MEMS)、微生化系统、表面科学、流体动力学等领域潜在的应用价值,各国学者们对纳米气泡的自身性质及影响因素已经开展了多方面的研究。但纳米气泡稳定性(反常的长寿)的原因仍然是未解决的问题之一。本文综述了纳米气泡的形成及影响因素,重点评述了纳米气泡稳定性理论,包括线张力理论、动态平衡理论、杂质理论和克努森气体理论等。同时,介绍了固液界面纳米气泡的应用,并展望了未来研究的重点和方向。 相似文献
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纳米通道内表面浸润性对气泡的作用 总被引:2,自引:0,他引:2
运用分子动力学模拟方法研究了在质量力驱动下不同浸润性壁面纳米通道中气泡的分布及其运动状况, 提出了一种统计纳米通道中气泡运动速度的方法. 结果显示, 在亲水性壁面的纳米通道中, 气泡位于通道中间, 气泡的运动速度接近但小于通道中心流速, 在势能强度较大时, 壁面吸附的分子较多, 气泡也较大, 反之则气泡较小; 对超疏水性壁面, 气泡则位于固壁附近, 两个壁面形成对称的一对气泡, 气泡的运动速度接近但大于边缘速度. 流体总的流动速度随着流体粒子与壁面粒子作用的减弱而增大, 滑移速度则逐渐从负转变为正. 相似文献
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固液界面纳米气泡的研究进展 总被引:6,自引:0,他引:6
根据经典热力学理论,在水中纳米级的气泡难以长期稳定存在.近年来却有大量的实验结果表明固液界面存在纳米气泡,原子力显微镜也直接观察到了纳米气泡.有关纳米气泡的研究具有巨大的理论和实际意义,它对表面科学、流体动力学、生物科学以及一些应用领域都有深远的影响.纳米气泡会引起流体在界面的滑移,减少流动阻力,并与表面粘附、胶体分散、矿石浮选、废渣处理等方面密切相关.目前关于纳米气泡的研究才刚刚开始,对于它的基本物化性质的了解还不多,但其重要性已经引起相关领域的极大关注.本文综述了从提出纳米气泡存在一直到实验证明的过程、纳米气泡的形成机制和形貌、分布特征等基本性质以及纳米气泡的存在对疏水长程作用和流体滑移的影响,并阐述了生物学中一些与纳米气泡存在有关的问题. 相似文献
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在T形微通道中,以错流剪切的分散方式实现了微米级分散气泡的制备,并以NaOH水溶液吸收CO2为对象,考察了气.液微分散体系的分散规律和传质性能.通过考察两相流速对气泡分散尺寸的影响,建立了预测气泡形成尺寸的数学模型.根据气泡的初始分散尺寸、流动阶段的体积变化以及传质完成后的尺寸,首次测定和区分了气泡形成阶段和运动阶段的传质量,建立了原位测定气泡分散流传质系数札的方法,并考察了两相流量对札的影响.结果表明,由于微通道中气泡的形成时间很短,形成阶段的传质量在总传质量中所占的比例很低.气泡分散流的传质系数主要受液相流量的影响,气相流量的影响基本可以忽略.基于实验结果,建立了计算传质系数鼠的无因次准数关联,计算结果与实验结果符合良好. 相似文献
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建立了气泡微萃取结合气相色谱/质谱技术(GC-MS)测定尿中咖啡因的方法.对影响萃取效率的实验条件进行了优化,确定了最佳萃取条件:三氯甲烷作为萃取溶剂,萃取溶剂暴露体积1 μL,气泡体积1.6 μL,搅拌速度300 r/min,萃取时间5 min,盐度15%(m/V),气泡与磁子间距离1 cm.在优化条件下,所建立方法在咖啡因浓度0.005~10 mg/L范围内有较好的线性关系,相关系数可达0.986,检出限为0.003 mg/L.在人尿液中添加不同浓度的咖啡因(0.050、0.500和5.000 mg/L),回收率为89.2%~107.5%,相对标准偏差小于8%(n=6). 相似文献
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C. W. Stewart 《Journal of Polymer Science.Polymer Physics》1970,8(6):937-955
The theory of homogeneous nucleation of bubbles is combined with an expression, for their rate of growth in elastomers to obtain approximate expressions for calculating the number of bubbles formed under a high degree of supersaturation. Experimental results are given for several elastomers with argon as the dissolved gas under a variety of foaming conditions. The theory adequately describes the manner in which the number of bubbles formed depends on the temperature, surface tension of the polymer, and permeability of the dissolved gas. 相似文献
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Mria?Fldvri 《Journal of Thermal Analysis and Calorimetry》2005,79(3):537-543
Summary Metal ions are adsorbed in the interlayer space and on the edges of clay minerals, leading to the uniform distribution of metal ions on atomic scale. However, additional processes can be resulted in the formation of nano and micro particles in the interlayer space as well as on the outer surfaces. The formation of nano and micro particles on clay minerals under environmental conditions are discussed here in metal ions (manganese, lead, zinc, and silver ions)/bentonite systems. Two-dimensional nano layer is formed in the interlayer space by the oxidation of manganese ions under atmospheric conditions. Three-dimensional particles are formed on the surfaces initiating by the metal ion adsorption on the deprotonated edge sites. The formation of micro particles on the surface can also be followed by the redox reaction of metal ions. 相似文献
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C. Zhang K. Khoshmanesh A. Mitchell K. Kalantar-zadeh 《Analytical and bioanalytical chemistry》2010,396(1):401-420
Dielectrophoretic (DEP) force is exerted when a neutral particle is polarized in a non-uniform electric field, and depends
on the dielectric properties of the particle and the suspending medium. The integration of DEP and microfluidic systems offers
numerous applications for the separation, trapping, assembling, transportation, and characterization of micro/nano particles.
This article reviews the applications of DEP forces in microfluidic systems. It presents the theory of dielectrophoresis,
different configurations, and the applications of such systems for particle manipulation and device fabrication. 相似文献
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综述了银基微纳米半导体光催化应用研究进展.指出银基微纳米半导体在可见光辐照下表现出良好的光催化性能(光催化降解有机物或光解水制氢制氧),目前的研究主要集中在简单的含银化合物、含银的异质结构、含银的多金属氧化物和含银的固溶体这几类;并从光催化原理和能隙调节手段入手阐述了决定其光催化性能的因素. 相似文献
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Zhang Y Wang L Liu X Yan Y Chen C Zhu J 《The journal of physical chemistry. B》2005,109(27):13091-13093
Nano and micro ZnO rods and arrays have been synthesized by a simple thermal evaporation approach on a cylindrical shape substrate. Most of the synthesized ZnO products are single crystalline with a hexagonal structure and grow along the [0001] direction. Individual protrusive ZnO rods and well-aligned arrays are two typical products in our work. The individual protrusive ZnO rods have diameters of 25 nm approximately 2.1 microm and lengths from several hundred nanometers to 40 microm, while in the well-aligned arrays, the diameter and length of each ZnO rod range from 60 nm to 1.2 microm and from 4 microm to 6 microm, respectively. The heating temperature and deposition position are two key points to control the diameters of the rods. The growth mechanism is discussed and proposed. The perfect crystalline ZnO rods with different scales from nanometer to micrometer are good models for the investigation of the size effect of physical and chemical properties of one-dimensional material. 相似文献
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We introduce a new mechanism to pump liquid in microchannels based on the directional growth and displacement of gas bubbles in conjunction with the non-directional and selective removal of the bubbles. A majority of the existing bubble-driven micropumps employs boiling despite the unfavorable scaling of energy consumption for miniaturization because the vapor bubbles can be easily removed by condensation. Other gas generation methods are rarely suitable for micropumping applications because it is difficult to remove the gas bubbles promptly from a pump loop. In order to eradicate this limitation, the rapid removal of insoluble gas bubbles without liquid leakage is achieved with hydrophobic nanopores, allowing the use of virtually any kind of bubbles. In this paper, electrolysis and gas injection are demonstrated as two distinctively different gas sources. The proposed mechanism is first proved by circulating water in a looped microchannel. Using H(2) and O(2) gas bubbles continuously generated by electrolysis, a prototype device with a looped channel shows a volumetric flow rate of 4.5-13.5 nL s(-1) with a direct current (DC) power input of 2-85 mW. A similar device with an open-ended microchannel gives a maximum flow rate of approximately 65 nL s(-1) and a maximum pressure head of approximately 195 Pa with 14 mW input. The electrolytic-bubble-driven micropump operates with a 10-100 times higher power efficiency than its thermal-bubble-driven counterparts and exhibits better controllability. The pumping mechanism is then implemented by injecting nitrogen gas bubbles to demonstrate the flexibility of bubble sources, which would allow one to choose them for specific needs (e.g., energy efficiency, thermal sensitivity, biocompatibility, and adjustable flow rate), making the proposed mechanism attractive for many applications including micro total analysis systems (microTAS) and micro fuel cells. 相似文献
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CaMoO4 micro/nano hollow spheres with three different sizes were prepared via a reverse-microemulsion route at room temperature. Through designing a novel thermochemical cycle, the relationship between thermodynamic properties of nano CaMoO4 and bulk CaMoO4 was built. Combined with in situ microcalorimetry, change regularities for the thermodynamic properties of the prepared CaMoO4 micro/nano materials and reaction systems were obtained. The results reveal that size effect has significant influence on thermodynamic properties of micro/nano materials and reaction systems. Along with the size decreasing, the standard molar enthalpy, standard molar Gibbs free energy and standard molar entropy of reaction of micro/nano reaction systems decreased, but the standard molar enthalpy of formation, standard molar Gibbs free energy of formation and standard molar entropy of micro/nano materials increased. 相似文献
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Two kinds of micro/nano sized fibrils based on cellulose (MFC) and polyvinyl alcohol (PVA) were used as reinforcer for epoxy resin (EP) with different contents in the range from 0 to 0.3 wt %. PVA nanofibers with diameter about 40–80 nm were fabricated by electrospinning technique. The analysis of mechanical properties showed that by both adding MFC and PVA to EP the fracture toughness was increased. The SEM results showed that micro/nano sized fibers dispersed throughout epoxy resin, prevented and changed the path of crack growth. 相似文献
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An attempt was made to investigate the potential of two widely used commercial nano and micro TiO2 photocatalysts in degradation and mineralization of a typical azo dye “ect blue 71” in water. A special circulating up-flow reactor with an UV-C-150 W lamp was employed and the influence of the operational parameters was investigated. The results showed that both the photolysis and photocatalysis cause decomposition simultaneously. Despite a half concentration, the nano TiO2 particles provide a nearly twice efficiency, and for the vital case of mineralization 98% reduction in COD after 120 min irradiation. The influence of turbidity of catalyst particles was determined with a novel method and was taken into account in kinetic studies. It was found that the bulk degradation by the OH radicals has a major role in the photocatalysis process. 相似文献