基于AFM的固液界面表面电荷密度测量方法（英文）

固液界面的表面电荷会影响微纳流体系统的流体阻力,因此如何测量固液界面的表面电荷密度以及分析表面电荷的产生机理对于研究表面电荷对流体阻力的影响具有较大的意义。提出了一种基于接触式AFM的固液界面表面电荷密度测量方法。基于该方法测量了浸在去离子水和0.01mol/L的NaCl溶液中的高硼硅玻璃和二氧化硅样本的表面电荷密度,并研究了溶液pH值对表面电荷的影响。研究结果表明高硼硅玻璃和二氧化硅由于表面硅烷基的电离带负电。溶液pH值和离子浓度的增加都会增加浸在去离子水和0.01mol/L的NaCl溶液中高硼硅玻璃和二氧化硅的表面电荷密度的绝对值。     

真空中固液界面的离子束分析研究

原位实时地高精度测量固液界面的元素或离子(电荷)组成和动态变化对于界面反应和相互作用研究非常重要,但是传统的高分辨离子束分析实验在真空环境中不能直接测量液体样品。本文研制了一种固体-液体界面探针,该探针使用氮化硅-铝纳米复合膜作为真空密封窗和电化学电极,利用复旦大学核微探针成功开展了真空中固体-液体界面探针0.01 mol/L氯化钡和1 mol/L氯化镧溶液样品固体-液体界面的卢瑟福背散射(RBS)分析和粒子激发X射线(PIXE)分析。实验结果表明,真空环境下,固液界面探针纳米薄窗可承受2 MeV He+离子注量为1.0×1018 ions/cm2的辐照。微区PIXE分析成功获得了固液界面探针结构的元素分布。通过对卢瑟福背散射能谱进行分析,获取了20 nm分辨的电极界面微米深溶液中的La, Cl元素浓度。在1 mol/L的LaCl3固液界面电极表面,负电压(–2.3 V)时电解质离子在电极表面高浓度聚集,正电压(+2.3 V)时电解质在电极表面呈低浓度分布,在约1 250 nm深处电解质溶液趋向于体浓度。     

硅（100）晶面上硅和二氧化硅的横向与纵向腐蚀速率

定义了硅表面上硅和二氧化硅的横向腐蚀速率 ,系统地测量了硅 (10 0 )晶面上的硅和二氧化硅在 4 0 %(质量分数 )氟化铵水溶液中的横向与纵向腐蚀速率 ,并和硅 (111)晶面上的测量结果进行了对比 .对比结果表明 ,尽管两种晶面上的硅和二氧化硅的腐蚀速率有明显的差别 ,其相应的表观活化能在误差范围内相同 .实验中还发现 ,溶液的温度为 38.2℃时 ,硅腐蚀过程中形成的气泡对硅的腐蚀速率有显著的影响 :开始时加速硅的腐蚀 ;但随着气泡在硅 /溶液界面的聚集 ,阻碍硅的腐蚀 .     

悬垂液滴研究及表面张力和润湿角测定

对光滑固体表面下悬挂的液滴进行了理论分析,建立了悬垂液滴特征尺寸R和H与液滴表面张力σL和固液界面润湿角θ之间的关系式,计算发现对于特定的ρ,σL,θ值,液滴质量m与固液界面润湿半径R、液滴高度H满足特殊的曲线关系.利用此关系可以同时测量液滴的表面张力σL以及固液界面间的润湿角θ.     

等离子体表面梯度硅沉积对环氧树脂电气性能的影响

环氧树脂作为常见的绝缘材料,在高压直流电场作用下易在其表面积累电荷,发生电场畸变,导致材料绝缘性能下降,影响电力系统运行可靠性。为改善气固界面的电荷特性和绝缘性能,在大气压等离子体射流技术的基础上,对环氧树脂表面进行等离子体梯度硅沉积处理。对改性前后环氧树脂表面理化特性、表面电导率、表面电荷消散和沿面耐压特性进行了多参数测量。实验结果表明,梯度改性对材料表面的物理形貌和化学组分均有明显影响,不同区域的电导率实现了梯度分布,加快了表面电荷消散速度,表面陷阱能级变浅;梯度改性后的样品沿面闪络电压提升幅度可达30.16%。通过等离子体表面梯度硅沉积处理能够改善环氧树脂表面电气性能,在高压直流设备的绝缘设计方面具有广阔的应用前景。     

核磁共振成像技术在液-固-液界面接触角测量中的应用

介绍了利用核磁共振成像的办法获得一般光学方法难以得到的水-破璃-油界面、水-玻璃-苯界面影像的实验工作,并利用得到的图像拟合了其界面接触角的值.实验中首次将核磁共振断面成像的办法应用到接触角影像分析中去,并且作了从气-固-液接触角测量到液-固-液接触角测量的有益尝试.     

微流控光学透镜阵列内芯表面的电润湿特性测量

采用特定的“导电基片／绝缘膜层”微透镜阵列内芯材料,研究其表面的介质上电润湿（EWOD）特性。利用图像采集与数据处理方法测量了0～60V电压范围内硫酸钠水溶液液滴在“不锈钢基片／Parylene绝缘层”芯片表面的接触角变化数据,通过EWOD理论模型计算得到硫酸钠溶液的表面张力值,此值与理论值相吻合。进而计算了内芯与液滴的界面张力,这种方法可用于一般固液界面张力的测量。     

液滴在气固交界面变形移动问题的光滑粒子流体动力学模拟

为准确模拟液滴在气固交界面变形移动问题,对基于连续表面张力模型的表面张力光滑粒子流体动力学方法进行了改进.改进方法采用新的边界处理方式和界面法向修正方法,即将固体边界虚粒子色函数值根据液面的位置进行相应设定以保证气-液-固三相交界处流体粒子的界面法向沿接触线法线方向,引入Brackbill提出的壁面附着力边界条件处理方法,对在气-液-固三相交界处的流体粒子及部分固体边界虚粒子的界面法向进行修正,修正前后保持法向模值不变,得到了含壁面附着力边界条件的表面张力算法.模拟了受壁面附着力影响的水槽中液面的变化过程、液滴润湿壁面过程和剪切气流驱动液滴在固体表面变形脱落过程,并与流体体积函数方法进行了对比.结果表明,该方法在处理壁面附着力问题时精度较高,稳定性较好,适合处理工程中液滴在气固交界面变形移动问题.     

拖曳效应对低相干动态光散射测量粒径的影响

低相干动态光散射技术利用低相干干涉计的特性,有效抑制了从浓悬浮液中散射的多次散射光,从而能够检测到的单散射光信号中获取颗粒的动态信息。该技术以单散射理论为解析基础,为避免多重散射的影响,测量区域一般局限于固-液界面附近。分析了固-液界面附近壁的拖曳效应对粒径测量值的影响。利用相位调制低相干动态光散射装置,对体积分数为10%的不同粒径的标准聚苯乙烯溶液进行了检测。通过对结果考虑拖曳效应进行修正,发现不同粒径的粒子在界面附近10～30μm范围内的测量值与给定粒径值标准偏差在5%以内。表明在低相干动态光散射光程可分割测量中,考虑拖曳效应的影响,可以对固-液界面附近的测量结果通过修正并得到准确的颗粒大小信息。     

表面增强喇曼散射(SERS)光谱中影响增强效应因素的实验研究(Ⅲ)

本文研究了苯甲酸水溶液的pH值,电极外加电位对银电极表面吸附苯甲酸SERS光谱表面增强效应的影响。实验结果表明,苯甲酸以—COO~-根负离子吸附于银电极表面。通过改变溶液的pH值,使苯甲酸吸附于粗糙银电极表面,溶液pH值影响电极表面吸附苯甲酸的面密度,电极外加电位影响—COO~-根离子与银电极间的电荷迁移,电极外加电位也影响苯甲酸在粗糙银电极表面的吸附。     

Short range attraction between two similarly charged silica surfaces

Using an atomic force microscope we measure the interaction between two identically charged silica surfaces in the presence of a saline solution. For pure NaCl the interaction is always repulsive. Upon addition of cobalt hexamine ions, Co(NH(3))(6)(+3), the repulsion is gradually suppressed and a pronounced attraction develops at distances much shorter than the screening length. Higher concentrations of cobalt hexamine turn the attraction back into repulsion. Measurements of surface charge renormalization by the trivalent cations provide their surface density and their association constant to the negatively charged silica surface. These estimates tend to exclude interaction between two condensed Wigner crystals as an explanation for the attraction.     

The Colloidal Probe Technique and its Application to Adhesion Force Measurements

Knowledge of the interaction forces between colloidal particles and surfaces is a precondition for understanding the stability of dispersed systems and adhesion phenomena. One of the methods available for direct measurement of surface forces is the atomic force microscope (AFM). Based on this method the so called “colloidal probe technique” was developed more than 10 years ago. Using a micron‐sized particle glued to the end of an AFM cantilever as the force sensor, this technique is predestined for the study of colloidal interactions. In this review we describe the colloidal probe technique and give an overview of its application in the field of adhesion forces.     

Tribological behavior of micro/nano-patterned surfaces in contact with AFM colloidal probe

In effort to investigate the influence of the micro/nano-patterning or surface texturing on the nanotribological properties of patterned surfaces, the patterned polydimethylsiloxane (PDMS) surfaces with pillars were fabricated by replica molding technique. The surface morphologies of patterned PDMS surfaces with varying pillar sizes and spacing between pillars were characterized by atomic force microscope (AFM) and scanning electron microscope (SEM). The AFM/FFM was used to acquire the friction force images of micro/nano-patterned surfaces using a colloidal probe. A difference in friction force produced a contrast on the friction force images when the colloidal probe slid over different regions of the patterned polymer surfaces. The average friction force of patterned surface was related to the spacing between the pillars and their size. It decreased with the decreasing of spacing between the pillars and the increasing of pillar size. A reduction in friction force was attributed to the reduced area of contact between patterned surface and colloidal probe. Additionally, the average friction force increased with increasing applied load and sliding velocity.     

Dehydration process in NaCl solutions under various external electric fields

Ionic motions at solid-liquid interface in supersaturated NaCl solutions have been investigated by molecular dynamics (MD) simulation for understanding crystal growth processes. The density profile in the vicinity of the interfaces between NaCl(100) and the supersaturated NaCl solution was calculated. Diffusion coefficients of water molecules in the solution were estimated as a function of distance from the crystal interface. It turned out that the structure and dynamics of the solution in the interfaces was different from those of bulk solution owing to electric fields depending on the surface charge. Therefore, the electric field was applied to the supersaturated solutions and dehydration phenomenon occurring in the process of the crystal growth was discussed. As the electric field increased, it was observed that the Na⁺ keeping strongly hydration structure broke out by the electric force. In supersaturated concentration, the solution structure is significantly different from that of dilution and has a complicated structure with hydration ions and clusters of NaCl. If the electric fields were applied to the solutions, the breakout of hydration structure was not affected with increasing the supersaturated ratio. This reason is that the cluster structures are destroyed by the electric force. The situation depends on the electric field or crystal surface structure.     

Electrostatic force of dust deposition originating from contact between particles and photovoltaic glass

Charged photovoltaic glass produces an electrostatic field. The electrostatic field exerts an electrostatic force on dust particles, thus making more dust particles deposited on the glass. In this paper, the contact electrification between the deposited dust particles and the photovoltaic glass is studied. Meanwhile, the surface charge density model of the photovoltaic glass and the electrostatic force of charged particles are analyzed. The results show that with the increasing of the particle impact speed and the inclination angle of the photovoltaic panel, the charges on particles increase to different degrees.Under a given condition, the electrostatic forces acting on the charged particles at different positions above the glass plate form a bell-shaped distribution at a macro level, and present a maximum value in the center of the plate. As the distance between the particle and the charged glass decreases, the electrostatic force exerted on the particle increases significantly and fluctuates greatly. However, its mean value is still higher than the force caused by gravity and the adhesion force,reported by some studies. Therefore, we suggest that photovoltaic glass panels used in the severe wind-sand environment should be made of an anti-static transparent material, which can lessen the dust particles accumulated on the panels.     

Imaging and tracking an electrostatic charge micro-domain by Kelvin force microscopy as evidence of water adsorption on mica surface

Muscovite mica is a widely accepted substrate for scanning probe microscopy (SPM) investigations. However, mica has intrinsic properties that alter samples and obstruct their analysis due to free charges build-up, ionic exchange and water adsorption taking place at the surface. In addition to interfacial phenomena, there is a growing interest in electrostatic charges on insulators as they are crucial in diverse applications. Despite the high demand for studies of this nature, experimental set-ups capable of resolving charge build-up at the micro-scale are still scarce and technically limited. Here, we report the imaging of surface charge dissipation on freshly cleaved mica by Kelvin-probe Force Microscopy (KPFM). A local electrostatic charge micro-domain was generated by friction between an atomic force microscope (AFM) tip and mica, and its decay was tracked by two-dimensional mapping using KPFM. We found time-dependent charge dissipation, which is attributed to the adsorption of water molecules on mica surface.     

Static polarizability effects on counterion distributions near charged dielectric surfaces: A coarse-grained Molecular Dynamics study employing the Drude model

Coarse-grained implicit solvent Molecular Dynamics (MD) simulations have been used to investigate the structure of the vicinal layer of polarizable counterions close to a charged interface. The classical Drude oscillator model was implemented to describe the static excess polarizability of the ions. The electrostatic layer correction with image charges (ELCIC) method was used to include the effects of the dielectric discontinuity between the aqueous solution and the bounding interfaces for the calculation of the electrostatic interactions. Cases with one or two charged bounding interfaces were investigated. The counterion density profile in the vicinity of the interfaces with different surface charge values was found to depend on the ionic polarizability. Ionic polarization effects are found to be relevant for ions with high excess polarizability near surfaces with high surface charge.     

Xe离子束辐照硼硅酸盐玻璃和石英玻璃效应对比研究

玻璃固化体作为放射性废物地质处置的第一道安全屏障,它的耐辐照性能研究至关重要.玻璃固化体主要网络结构硅氧四面体与石英玻璃的硅氧四面体是一致的,所以这里用石英玻璃代替玻璃固化体作为研究对象.本文采用Xe离子在相同条件下辐照石英玻璃和硼硅酸盐玻璃.利用纳米压痕技术和椭圆偏振仪表征了辐照前后样品的硬度、模量以及折射率的变化情况.结果表明:硼硅酸盐玻璃和石英玻璃的硬度均随着辐照剂量的增大而减小,硼硅酸盐玻璃的模量随着辐照剂量的增大而减小;石英玻璃的模量随着辐照剂量的增大而增大.模量的变化可能和密度的变化有关,这点与折射率的结果相符.     

电解质浓度对胶体粒子表面有效电荷的影响

胶体粒子的表面有效电荷是决定胶体性质的重要物理量,但溶液环境(如电解质溶液浓度)是否影响其数值至今尚无统一认识,近年来的一些研究工作给出了存在争议的不同结果和假设.在直接实验测量方面,由于电解质离子和胶体表面吸附离子的置换,粒子表面基团的不完全电离和胶体粒子对离子吸附的共同作用,使得对这类粒子在不同溶液环境下的表面有效电荷的测量和变化机理的认识极为困难.针对该问题,本文测定了羧基和磺酸基修饰的聚苯乙烯胶体颗粒在不同粒子浓度和HCl浓度下的电导率,由于两种粒子与HCl电离产生的阳离子相同(均为H+),可根据电导率-数密度法(迁移法)得到胶体颗粒表面有效电荷数.通过实验结果分析,明确了HCl浓度以及粒子数密度对胶体粒子表面电荷的影响规律以及表面电荷随HCl浓度增大的原因.除此之外,羧基修饰颗粒比磺酸基修饰颗粒的表面电荷随HCl浓度变化更快;对于同一HCl浓度,磺酸基修饰胶体表面电荷不受粒子数密度影响,而羧基修饰胶体颗粒却与之相关.基于粒子表面电荷的理论模型,对这些问题都给出了相应的解释.