基于MEMS粘附问题中关键表面力的分析

粘附是MEMS器件在加工、操作过程中特有的现象,根据微机械中作用力的尺度效应与表面效应,分析表面张力、范得瓦耳斯力、静电力对粘附的影响机理,同时给出了抗粘附的常用的技术方法.     

Atomic force microscopy study on chlorpromazine‐induced morphological changes of living HeLa cells In Vitro

Chlorpromazine (CPZ)‐induced morphological changes of living human cervical carcinoma cells were investigated by atomic force microscopy in near physiological condition. The results showed that the cell morphology changed visibly with time in the presence of CPZ (>21 µM). The cell membrane shrank gradually and detached finally from the substrate. After being treated with CPZ for 50 min, the cell volume increased by about 27.6% while its projective area (cell adhered to the substrate) decreased by about 12%. The mechanism was also discussed. SCANNING 31: 259–265, 2009. © 2010 Wiley Periodicals, Inc.     

Effects of tip-sample forces and humidity on the imaging of DNA with a scanning force microscope

We have investigated the effects of tip-sample forces and relative humidity when using a scanning force microscope (SFM) to image DNA molecules adsorbed on fresh mica. As the force between the tip and the sample increases, the apparent height of the DNA molecules decreases. After being imaged with high forces, the DNA molecules recover partially in their apparent height, indicating that a plastic deformation of the DNA has been induced by the scanning tip. At low humidities, DNA molecules can be imaged with a force up to 150 nN during the scanning without obvious damages. At higher humidities, however, the DNA molecules can be dissected or swept away by the tip even at a tip-sample force of 30 nN. The net force between the tip and the molecules is the vector sum of several forces, the dominant components of which are the elastic force due to the cantilever bending and the capillary force resulting from the water meniscus formed between the tip and the sample surface. When the relative humidity of the imaging environment is increased, the capillary force becomes stronger.     

Surface force microscope observations of corrosive tribological wear on single crystal NaNO3 exposed to moist air

Simultaneous tribological loading and exposure to a chemically reactive environment can yield wear processes not produced by either stimulus alone. We report surface force microscopic (SFM) observations of cleaved, single crystal NaNO₃ in air, where tribological loading was provided by the SFM tip itself and chemical exposure was due to controlled introduction of water vapor at relative humidities from 10 to 65%. Scanning in the contact mode with nN loads at 30–50% relative humidity produces readily visible surface modifications, including preferential removal of material along steps. Material transfer along the surface can yield parallel ridges and depressions tens of nanometer high. In contrast, scanning in the tapping mode under certain humidity conditions produces localized deposition, possibly reflecting the dehydration of solvated ions and subsequent incorporation into the solid phase. We discuss the influence of contact force, tip velocity, relative humidity, and possible mechanochemistry on the rates of wear and deposition.Department of Mechanical Engineering, Kansai University, Osaka 564, Japan.     

Roles of cell adhesion molecules nectin and nectin-like molecule-5 in the regulation of cell movement and proliferation

In response to chemoattractants, migrating cells form protrusions, such as lamellipodia and filopodia, and structures, such as ruffles over lamellipodia, focal complexes and focal adhesions at leading edges. The formation of these leading edge structures is essential for directional cell movement. Nectin-like molecule-5 (Necl-5) interacts in cis with PDGF receptor and integrin alpha(v)beta(3), and enhances the activation of signalling molecules associated with these transmembrane proteins, which results in the formation of leading edge structures and enhancement of directional cell movement. When migrating cells come into contact with each other, cell-cell adhesion is initiated, resulting in reduced cell velocity. Necl-5 first interacts in trans with nectin-3. This interaction is transient and induces down-regulation of Necl-5 expression at the cell surface, resulting in reduced cell movement. Cell proliferation is also suppressed by the down-regulation of Necl-5, because the inhibitory effect of Necl-5 on Sprouty2, a negative regulator of the Ras signalling, is diminished. PDGF receptor and integrin alpha(v)beta(3), which have interacted with Necl-5, then form a complex with nectin, which initiates cell-cell adhesion and recruits cadherin to the nectin-based cell-cell adhesion sites to form stable adherens junctions. The formation of adherens junctions stops cell movement, in part through inactivation of integrin alpha(v)beta(3) caused by the trans-interaction of nectin. Thus, nectin and Necl-5 play key roles in the regulation of cell movement and proliferation.     

Analysis of effect of nanoporous alumina substrate coated with polypyrrole nanowire on cell morphology based on AFM topography

In this study, in situ electrochemical synthesis of polypyrrole nanowires with nanoporous alumina template was described. The formation of highly ordered porous alumina substrate was demonstrated with Atomic Force Microscopy (AFM) and Scanning Electron Microscopy (SEM). In addition, Fourier transform infrared analysis confirmed that polypyrrole (PP) nanowires were synthesized by direct electrochemical oxidation of pyrrole. HeLa cancer cells and HMCF normal cells were immobilized on the polypyrrole nanowires/nanoporous alumina substrates to determine the effects of the substrate on the cell morphology, adhesion and proliferation as well as the biocompatibility of the substrate. Cell adhesion and proliferation were characterized using a standard MTT assay. The effects of the polypyrrole nanowires/nanoporous alumina substrate on the cell morphology were studied by AFM. The nanoporous alumina coated with polypyrrole nanowires was found to exhibit better cell adhesion and proliferation than polystyrene petridish, aluminum foil, 1st anodized and uncoated 2nd anodized alumina substrate. This study showed the potential of the polypyrrole nanowires/nanoporous alumina substrate as biocompatibility electroactive polymer substrate for both healthy and cancer cell cultures applications.     

Effect of aging on the morphology of bitumen by atomic force microscopy

Effect of aging on the morphology of bitumen was investigated. Two bitumens were aged according to the thin film oven test (TFOT), pressure aging vessel (PAV) test and ultraviolet (UV) radiation, respectively. The morphology of the binders before and after aging was characterized by atomic force microscopy. The physical properties and chemical compositions of the binders were also measured. The results showed that aging affected the bitumen morphology significantly. Aging increased the overall surface stiffness of the bitumen and made the bitumen surface more solid-like. The extent of these changes was dependent on aging conditions. TFOT decreased the contrast between the dispersed domains and the matrix, which contributed to the single-phase trend of the binders. The effect of PAV aging on morphology of the binders was dependent on the base bitumen. In one case, it further accelerated the single-phase trend of bitumen in comparison with that after TFOT. In the other case, it caused the phase separation of bitumen. In both cases, PAV aging increased the surface roughness of the binders obviously. As a result of UV aging, the contrast between the matrix phase and dispersed phase was increased due to the difference in sensitivity to UV radiation of the bitumen molecules, which caused or further promoted the phase separation in the binders. Regardless of the aging procedure carried out, a strong correlation was observed between the changes in morphology and physical properties as well as chemical compositions of the binders before and after aging.     

Atomic force microscopy investigation of the dependence of cellular elastic moduli on glutaraldehyde fixation

The atomic force microscope (AFM) has provided nanoscale analyses of surfaces of cells that exhibit strong adhesive and cell spreading properties. However, it is frequently reported that prior fixation is required for reliable imaging of cells with lower adhesive properties. In the present study, the AFM is used to assess the effects of fixation by glutaraldehyde on the elastic modulus of a human rhabdomyosarcoma transfectant cell line RDX2C2. Our results show a sharp increase in the elastic modulus for even mild fixation (0.5% glutaraldehyde for 60 s), accompanied by a dramatic improvement in imaging reproducibility. An even larger increase is seen in NIH-3T3 mouse fibroblasts, although in that case fixation is not typically necessary for successful imaging. In addition, our results suggest that treatment with glutaraldehyde restricts the content of the resulting images to features nearer to the cell surface.     

Elastic force of red blood cell membrane during tank-treading motion: Consideration of the membrane's natural state

The elastic force of a red blood cell (RBC) membrane during its tank-treading motion was estimated using a three-dimensional spring network model. An RBC membrane was modelled by an assembly of triangular elements in which stretch/compression and bending springs were placed to express planar shear and out-of-plane bending deformations, respectively. An areal incompressibility of the membrane and a volumetric constraint on the entire RBC were taken into account. Different natural states of an RBC membrane were considered by adjusting reference lengths and angles of the stretch/compression and bending springs, respectively. An elastic motion simulation was conducted using the spring network model to reproduce a tank-treading motion of the membrane for a constant biconcave discoid RBC under a fluid shear force. Given the simulated tank-treading motion, an additional membrane elastic force due to the motion was determined from the elastic energy changes during the motion. It was confirmed that the natural state of the RBC membrane should be nonuniform to generate the additional elastic force. Greater spring constants and greater natural state nonuniformity induced a greater additional elastic force, and the elastic force was regarded as a resistance against the tank-treading motion. Additional elastic forces due to the membrane tank-treading motion for different sets of spring constants and natural state nonuniformity values were determined, and they were compared with fluid shear forces at shear rates within the range of which a transition between tank-treading and tumbling motions of an RBC occurs in experiments. The results suggested that for the experimentally measured elastic moduli, natural state nonuniformity in a physiological state is moderate between that for a spherical or flat shape and that for the biconcave shape. Moderate nonuniformity was also confirmed by a simulated RBC shape in a minimum state of elastic energy.     

约束成型基底微观特征对阻聚区及黏附力的影响

为了减小约束投影快速3D打印工艺中黏附力对工艺可靠性及打印速度的影响,提出了一种多孔透明支撑板+PDMS膜低成本实现阻聚区的方案,并围绕阻聚区形成的两个关键因素-基底透光性和气体渗透性及其影响阻聚区和黏附力的规律进行研究。通过激光加工方法制备了具有微孔阵列的石英玻璃基底,通过对基底透光性、透氧性以及氧阻聚区厚度的实验测量,研究了基底微观几何特征及光照强度、氧气浓度等工艺要素对阻聚区厚度的影响规律,并通过3D打印试验,初步研究了不同基底条件下固化层在基底的黏附力。结果表明,基底微孔影响基底的透光率以及透氧性能,所制备的具有不同几何特征微孔的基底透光率均大于84%;通过调控氧浓度、光照强度以及基底微结构特征可以控制氧阻聚区的厚度;基底及供氧条件影响阻聚区的厚度从而影响剥离力。采用本文制备的约束基底打印零件过程中可以形成阻聚区,从而显著减小剥离力,在本文的实验条件下,固化层从基底的平均剥离力由26.4 N降至5.4 N。     

Effect of interlayer on structure and performance of anode-supported SOFC single cells

To lower the operating temperatures in solid oxide fuel cell (SOFC) operations, anode-supported SOFC single cells with a single dip-coated interlayer were fabricated and the effect of the interlayer on the electrolyte structure and the electrical performance was investigated. For the preparation of SOFC single cells, yttria-stabilized zirconia (YSZ) electrolyte, NiO-YSZ anode, and 50% YSZ-50% strontium-doped lanthanum manganite (LSM) cathode were used. In order to characterize the cells, scanning electron microscopy (SEM) and atomic force microscopy (AFM) were utilized and the gas (air) permeability measurements were conducted for gas tightness estimation. When the interlayer was inserted onto NiO-YSZ anode, the surface roughness of anode was diminished by about 40% and dense crack-free electrolytes were obtained. The electrical performance was enhanced remarkably and the maximum power density was 0.57W/cm(2) at 800 degrees C and 0.44W/cm(2) at 700 degrees C. On the other hand, the effect of interlayer on the gas tightness was negligible. The characterization study revealed that the enhancement in the electrical performance was mainly attributed to the increase of ion transmission area of anode/electrolyte interface and the increase of ionic conductivity of dense crack-free electrolyte layer.     

Effects of adsorbed water and sample aging in air on the μN level adhesion force between Si(100) and silicon nitride

The microscale adhesion force of single crystal silicon (100) to silicon nitride was studied using a newly developed micro/nanoadhesion measurement apparatus. The effect of water adsorption on adhesion between clean surfaces and surfaces aged in air was determined. During experiments, varying relative humidity (RH) controlled water adsorption. Clean and aged samples showed measurably changed water adsorption and adhesion above 60% RH only, and aged samples showed more water adsorption and adhesion than clean ones above 90% RH. A contaminant film grew to a saturated thickness of about 6 Å over 50 days of aging, and the film changed surface chemistry which resulted in higher contact angle. The contaminated surface with higher contact angle exhibited more affinity for water and microadhesion on the molecular scale, which is contrary to the common interpretation of contact angle data. The divergence of water adsorption and adhesion force behavior between clean and aged samples above 90% RH may indicate that the Kelvin radius became comparable to a characteristic length on the contaminated surface at high RH. A molecular model is proposed in which the contaminant film provides porosity, which allows capillary condensation and the growth of a multilayer water film.     

Effect of Zn doping on the sublimation rate of pentaerythritol tetranitrate using atomic force microscopy

A series of Zn ion‐doped pentaerythritol tetranitrate (PETN) nanoislands in the form of thin films were prepared on Si substrates using spin coating. The effect of Zn concentrations on the sublimation energy was investigated by atomic force microscopy (AFM). The pure and Zn‐doped nanoislands are imaged by AFM in contact mode at room temperature after annealing isothermally for a given time. The volume of the islands starts to decrease after annealing at 45°C for pure PETN, whereas Zn‐doped nanoislands start to decrease in height and volume after annealing at 55–58°C. The minimum activation energy is found to be 29.7 Kcal/mol for 1,000 ppm Zn concentration. These studies are important for the long‐term stabilization of PETN. SCANNING 31: 181–187, 2009. © 2009 Wiley Periodicals, Inc.     

Effect of hole perpendicularity error and squeeze force on the mechanical behaviors of riveted joints

In the automatic drilling and riveting process, the perpendicular error of the hole is inevitable, which has a great influence on the assembly quality. In the current research, the shear and pull-out behaviors of riveted joints under different perpendicularity errors and squeeze forces were investigated and compared by the quasi-static tests. The fracture of the failed samples was characterized by a scanning electron microscope and the formation process of fracture was discussed. The failure mechanisms of riveted joints were analyzed in detail to guide engineering applications. The test results demonstrated that the shear load and pull-out load of riveted joints increased slightly with the increase of the tilt angle from 0° to 4°. The perpendicularity error did not affect the shear and pull-out failure modes of the riveted joints. However, the squeeze force had a significant effect on the failure modes of the pull-out samples. Fracture analysis showed that the failure of all shear samples occurred at the rivet shaft. Besides, when the squeeze force increased from 15 kN to 23 kN, the failure modes of the pull-out samples changed from the sheet to the rivet itself.     

Analysis of force curves obtained on the live cell membrane using chemically modified AFM probes

Force curves were obtained on the live cell surface using an atomic force microscope mounted with a modified tip with the bifunctional covalent crosslinker, disuccinimidyl suberate, which forms a covalent bond with amino-bearing molecules on the cell surface. A ramp delay time of 1.0 s was introduced before the start of the retraction regime of the force curve to increase the stationary reaction time between the crosslinkers on the tip and the amino groups on the cell surface. While live cell surface responses to forced contact with a non-functionalized tip rarely showed evidence of tip–cell interaction, those obtained with modified tips gave clear indication of prolonged adhesion which was terminated by a single step release of the tip to its neutral position. Under the given experimental conditions of this work, 58% of a total of 198 force curves gave only one jump and 70% of those with one jump gave the final rupture force of 4.5±0.22 nN. The result emphasized the uniqueness of the observed mechanical response of the cell surface when probed with chemically modified tips.     

调心托辊和带式输送机参数对纠偏力的影响

对调心托辊进行了受力分析,得出了纠偏力的理论计算公式,并分析了调心托辊和带式输送机的参数对纠偏力的影响,为带式输送机的设计与安装提供了理论依据。     

Investigation on the liquid water droplet instability in a simulated flow channel of PEM fuel cell

To investigate the characteristics of water droplets on the gas diffusion layer from both top-view and side-view of the flow channel, a rig test apparatus was designed and fabricated with prism attached plate. This experimental device was used to simulate the growth of a single liquid water droplet and its transport process with various air flow velocity and channel height. Not only dry condition but also fully humidified condition was also simulated by using a water absorbing sponge. The detachment height of the water droplet with dry and wet conditions was measured and analyzed. It was found that the droplet tends towards becoming unstable by decreased channel height, increased flow velocity or making a gas diffusion layer (GDL) dryer. Also, peculiar behavior of the water droplet in the channel was presented like attachment to hydrophilic wall or sudden breaking of droplet in case of fully hydrated condition. The simplified force balance model matches with experimental data as well.     

Effect of friction and adhesion on the load–displacement of a spherical probe in contact with a compliant incompressible elastic coating

The mechanical properties of thin films are extracted from the measured load displacement relation in a contact test conducted using micro or nano instruments. At this micro or nano force scale, the adhesion and friction operating between the test tip and thin film surface will contribute to the deformation. The well established Johnson–Kendall–Roberts (JKR) theory provided a relationship between the normal load and elastic central displacement for the adhesion contact. But because of its semi-infinite half-space hypothesis, the standard JKR theory is not applicable to thin film contact problem. Experimental verification demonstrates the numerical version of JKR theory is suitable for compliant thin film adhesion analysis, but it does not include the friction effect. In this paper, the load–displacement relation of totally bonded friction contact with adhesion is studied and compared with that of frictionless case. The practical thin film contact will lie in these two limits. The effect of friction to load and displacement seems very small except for the transition range from film to substrate response. Empirical expressions for the contact compliance are obtained from the detailed finite element study.