Numerical Analysis of the Adhesive Forces in Nano-Scale Structure

Nanohairs, which can be found on the epidermis of Tokay gecko＇s toes, contribute to the adhesion by means of van der Waals force, capillary force, etc. This structure has inspired many researchers to fabricate the attachable nano-scale structures. However, the efficiency of artificial nano-scale structures is not reliable sufficiently. Moreover, the mechanical parameters related to the nano-hair attachment are not yet revealed qualitatively. The mechanical parameters which have influence on the ability of adhesive nano-hairs were investigated through numerical simulation in which only van der Waals force was considered. For the numerical analysis, finite element method was utilized and van der Waals force, assumed as 12-6 Lennard-Jones potential, was implemented as the body force term in the finite element formulation.

Silk fibroin-based biopolymer composite binders with gradient binding energy and strong adhesion force for high-performance micro-sized silicon anodes

Micro-sized silicon anodes have shown much promise in large-scale industrial production of high-energy lithium batteries.However,large volume change(>300%)of silicon anodes causes severe particle pulverization and the formation of unstable solid electrolyte interphases during cycling,leading to rapid capacity decay and short cycle life of lithium-ion batteries.When addressing such issues,binder plays key roles in obtaining good structural integrity of silicon anodes.Herein,we report a biopolymer composite binder composed of rigid poly(acrylic acid)(PAA)and flexible silk fibroin(SF)tailored for micro-sized silicon anodes.The PAA/SF binder shows robust gradient binding energy via chemical interactions between carboxyl and amide groups,which can effectively accommodate large volume change of silicon.This PAA/SF binder also shows much stronger adhesion force and improved binding towards high-surface/defective carbon additives,resulting in better electrochemical stability and higher coulombic efficiency,than conventional PAA binder.As such,micro-sized silicon/carbon anodes fabricated with novel PAA/SF binder exhibit much better cyclability(up to 500 cycles at 0.5 C)and enhanced rate capability compared with conventional PAA-based anodes.This work provides new insights into the design of functional binders for high-capacity electrodes suffering from large volume change for the development of nextgeneration lithium batteries.

Direct measurement and theoretical prediction model of interparticle adhesion force between irregular planetary regolith particles

Interparticle adhesion force has a controlling effect on the physical and mechanical properties of planetary regolith and rocks.The current research on the adhesion force of planetary regolith and rock particles has been primarily based on the assumption of smooth spherical particles to calculate the intergranular adhesion force;this approach lacks consideration for the adhesion force between irregular shaped particles.In our study,an innovative approach was established to directly measure the adhesion force between the arbitrary irregular shaped particles;the probe was modified using simulated lunar soil particles that were a typical representation of planetary regolith.The experimental results showed that for irregular shaped mineral particles,the particle size and mineral composition had no significant influence on the interparticle adhesion force;however,the complex morphology of the contact surface predominantly controlled the adhesion force.As the contact surface roughness increased,the adhesion force gradually decreased,and the rate of decrease gradually slowed;these results were consistent with the change trend predicted via the theoretical models of quantum electrodynamics.Moreover,a theoretical model to predict the adhesion force between the irregular shaped particles was constructed based on Rabinovich’s theory,and the prediction results were correlated with the experimental measurements.

Adhesion forces for water/oil droplet and bubble on coking coal surfaces with different roughness

Surface roughness plays a significant role in floatability of coal.In the present paper,coking coal surface was polished by three different sandpapers and the surface properties were characterized by contact angle and roughness measurements.The effect of surface roughness on floatability was investigated by adhesion force measurement system for measuring interaction forces between droplets/bubbles and coking coal surfaces with different roughness.The results showed that the contact angle decreased with increasing roughness yet the adhesion force between the water droplet and coal surface increased owing to the increased contact line and the appearance of line pinning.Maximum adhesion forces between water and surfaces were 111.70,125.48,and 136.42μN when the roughness was 0.23,0.98,and 2.79 μm,respectively.In contrast,under a liquid environment,the adhesion forces between air bubble/oil droplet and coal surfaces were decreased with increasing roughness because of the restriction by water.Maximum adhesion forces of increasing roughness were 97.14,42.76,and 17.86 μN measured at interfaces between air bubble and coal surfaces and 169.48,145.84,and 121.02 lN between oil droplet and surfaces,respectively.Decreasing roughness could be beneficial to the spreading of oil droplets and the adhesion of bubbles which is conducive to flotation separation.

Influence of atomic force microscope(AFM) probe shape on adhesion force measured in humidity environment

In micro-manipulation, the adhesion force has very important influence on behaviors of micro-objects. Here, a theoretical study on the effects of humidity on the adhesion force is presented between atomic force microscope （AFM） tips and substrate. The analysis shows that the precise tip geometry plays a critical role on humidity depen- dence of the adhesion force, which is the dominant factor in manipulating micro-objects in AFM experiments. For a blunt （paraboloid） tip, the adhesion force versus humidity curves tends to the apparent contrast （peak-to-valley corrugation） with a broad range. This paper demonstrates that the abrupt change of the adhesion force has high correla- tion with probe curvatures, which is mediated by coordinates of solid-liquid-vapor contact lines （triple point） on the probe profiles. The study provides insights for further under- standing nanoscale adhesion forces and the way to choose probe shapes in manipulating micro-objects in AFM experiments.

Efficient Preparation of Nanoparticle-Reinforced Nickel-based Composite Coating with Highly Preferred(220)Orientation

Nanoparticle-reinforced metal matrix composite coatings have significant potential in mechanical part surface strengthening owing their excellent mechanical properties.This paper reports a phenomenon in which the grain orientation gradually evolves to(220)as the deposition current density increases when preparing nanoparticle-reinforced nickel-based composite coatings through jet electrodeposition(JED).During the preparation of the Ni-SiC composite coatings,the deposition current density increased from 180 A/dm2 to 220 A/dm2,and TC(220)gradually increase from 41.4%to 97.7%.With an increase of TC(220),the self-corrosion potential increases from−0.575 to−0.477 V,the corrosion current density decreases from 9.52μA/cm^2 to 2.76μA/cm^2,the diameter of the corrosion pits that after 10 days of immersion in a 3.5 wt%NaCl solution decreases from 278–944 nm to 153–260 nm,and the adhesion of the coating increases from 24.9 N to 61.6 N.Compared a conventional electrodeposition(CED),the Ni-SiC composite coating using JED has the advantages of a smooth surface morphology,high corrosion resistance,and strong adhesion,which are more obvious with an increase in TC(220).

Stability of focal adhesion enhanced by its inner force fluctuation

Cells actively sense and respond to mechanical signals from the extracellular matrix through focal adhesions. By representing a single focal adhesion as a cluster of slip bonds, it has been demonstrated that the cluster often became unstable under fluctuated forces. However, an unusual case was also reported, where the stability of the cluster might be substantially enhanced by a fluctuated force with a relatively low fluctuation frequency and high fluctuation amplitude.Such an observation cannot be explained by the conventional fracture theory of fatigue. Here, we intensively investigate this intriguing observation by carrying out systematic parametric studies. Our intensive simulation results indicate that stability enhancement of this kind is in fact quite robust, which can be affected by the stochastic features of a single bond and the profile of the fluctuated forces such as the average value of bond force. We then suggest that the fluctuation of traction force within a focal adhesion might enhance its stability in a certain way.

FPGA Implementation of Extended Kalman Filter for Parameters Estimation of Railway Wheelset

It is necessary to know the status of adhesion conditions between wheel and rail for efficient accelerating and decelerating of railroad vehicle.The proper estimation of adhesion conditions and their real-time implementation is considered a challenge for scholars.In this paper,the development of simulation model of extended Kalman filter(EKF)in MATLAB/Simulink is presented to estimate various railway wheelset parameters in different contact conditions of track.Due to concurrent in nature,the Xilinx®System-on-Chip Zynq Field Programmable Gate Array(FPGA)device is chosen to check the onboard estimation ofwheel-rail interaction parameters by using the National Instruments(NI)myRIO®development board.The NImyRIO®development board is flexible to deal with nonlinearities,uncertain changes,and fastchanging dynamics in real-time occurring in wheel-rail contact conditions during vehicle operation.The simulated dataset of the railway nonlinear wheelsetmodel is tested on FPGA-based EKF with different track conditions and with accelerating and decelerating operations of the vehicle.The proposed model-based estimation of railway wheelset parameters is synthesized on FPGA and its simulation is carried out for functional verification on FPGA.The obtained simulation results are aligned with the simulation results obtained through MATLAB.To the best of our knowledge,this is the first time study that presents the implementation of a model-based estimation of railway wheelset parameters on FPGA and its functional verification.The functional behavior of the FPGA-based estimator shows that these results are the addition of current knowledge in the field of the railway.

A MODEL FOR COMPUTATIONAL INVESTIGATION OF ELASTO-PLASTIC NORMAL AND TANGENTIAL CONTACT CONSIDERING ADHESION EFFECT

With the rapid development of Micro-Electro-Mechanical System(MEMS),we enter a field in which the surface effects have dominated many of the micro-scale phenomena,and the adhesive contact is one of the focuses.In this paper,a feasible model for finite element computation is presented via a macroscopic and microscopic combination approach,in which the adhesive forces are simulated by some non-linear spring elements considering the softening stage.Two basic problems concerning the adhesion effect were considered;through specific quantitative analysis,the results show a consistency with the current elastic continuum theories of adhesion and a brief investigation into the effects of adhesion on plastic deformation and tangential contact will be carried out as well.

Internal limiting membrane dragging and peeling:a modified technique for macular holes closure surgery

AIM:To introduce a modified technique of internal limiting membrane(ILM)centripetal dragging and peeling to treat idiopathic macular hole(IMH)and to observe the ILM-retina adhesive forces.METHODS:Twenty-six consecutive patients with stage 3 to 4 IMH and followed up at least six months were enrolled.All patients underwent complete par plana vitrectomy,ILM dragging and peeling,fluid and gas exchange,15%C3 F8 tamponade and 2-week prone position.The best corrected visual acuity,macular hole evaluation by optical coherence tomography,and complications were evaluated.RESULTS:The mean diameter of IMH was 524±148μm(range:201-683μm),with 21 cases(80.8%)greater than 400μm.ILM dragging and peeling were successfully performed in all cases.Most of the ILM-retina adhesive forces are severe(42.3%,11/26),followed by mild(38.5%,10/26),and moderate(19.2%,5/26).The mean follow-up duration was 21.2±6.1 mo.The IMH was closed in 25(96.3%)eyes.Visual acuity(logMAR)improved significantly from 1.2±0.6 preoperatively to 0.7±0.5 postoperatively(P<0.001).CONCLUSION:Preexisting ILM-retina adhesive force is found in IMH patients.With assistance of this force,this modified technique may help to release the IMH edges and improve the closure rate of large IMH.

Morphology and Mechanical Characteristics of Monolayer and Multilayer Ir Coating by Double Glow Plasma

Multilayer iridium coating was manufactured on tungsten carbide substrates by a double glow plasma process.As comparison,monolayer was also produced.The microstructure and morphology were observed using scanning electron microscopy.Grain orientation and phase were determined using X-ray diffraction.The residual stress of the coating was studied by glancing incidence X-ray diffraction.The adhesive force of the coating was measured by a scratch tester.The results showed that both monolayer and multilayer had a polycrystalline phase with a strong（110） reflection.The coating had an excellent adhesion with no evidence of delamination.The adhesive force of the monolayer and multilayer was about 50 and 43 N,respectively.The interfacial reaction between the substrate and the layer occurred and a new WIr phase was found due to the high-temperature deposition process.The residual stress in the monolayer and multilayer was-1.6 and-1.1 GPa,respectively.

Exploration of the enhanced performances for silk fibroin/sodium alginate composite coatings on biodegradable Mg-Zn-Ca alloy

To expand the future clinic applications of biodegradable magnesium alloy,polymer coatings with excellent biocompatibility are the keys to solve the local alkalinity and rapid hydrogen release.Natural-organic silk fibroin provides an approach to fabricate a protective coating on biomedical Mg-Zn-Ca alloy,however,the adhesion force and mechanical properties of the coating on substrates are ought to be further improved without any chemical conversion/intermediate layer.Hereby,based on VUV/O;surface activation,a hybrid of silk fibroin and sodium alginate is proposed to enhance the adhesion force and mechanical properties of the composite coatings on hydrophilic Mg-Zn-Ca alloy surfaces.Various mass ratios of sodium alginate addition were investigated to achieve the optimum coating strategy.The nanoscratch test and nanoindentation test confirmed that the adhesion force was tripled and mechanical properties index was significantly improved when the mass ratio of silk fibroin/sodium alginate was 70/30 compared to pure silk fibroin or sodium alginate coatings.Meanwhile,the corrosion rate of the coated Mg-Zn-Ca alloy was significantly delayed with the addition of sodium alginate,resulting in a reaction layer during corrosion process.Furthermore,the mechanisms for both adhesion and corrosion processes were discussed in detail.Our findings offer more possibilities for the controllable surface performance of degradable metals.

NEW MECHANISM OF LIMITED-SLIP DIFFERENTIAL

According to property requirement of differential, create a new mechanism, which is a combination of a paralleogram linkage and a inverse parallelogram linkage,to replace conventional bevel gears of differential and point out that using the new mechanism the differential can meet the needs of the requirements of torque and speed of the two axle shafts. The instantaneous speed ratio (ISR) which is the left and right half-shaft with respect to differential shell is variable. The calculating result of the locking factor of the new mechanism is up to 3. The limited-slip capability increase twice. The mechanism is an ideal new type of mechanism of differential.

Effect of dilute acid treatment on adhesion properties of Longmaxi black shale

Properties of shale in an acid environment are important when acid or CO2 is injected into geologic formations as a working fluid for enhanced oil and gas recovery,hydraulic fracturing and reduced fracture initiation pressure.It has previously been shown that acid fluids can enhance the formation conductivity and decrease the hardness of shale.However,less is known about the effect of dilute acid on the adhesion properties of shale.In the study,shale samples are characterized in detail with advanced analysis.Adhesion properties of shale via dilute acid treatment were revealed by atomic force microscopy(AFM)for the first time.Results indicate that acid treatment can greatly enhance adhesion forces of the shale surface.After acid treatment,the average adhesion forces show a platform-like growth with an increase in loading force.Through analysis of results from AFM,scanning electron microscopy,and X-ray diffraction,we affirm that the enhanced adhesion forces are mainly from increased specific surface area and reduced elastic modulus.The results presented in this work help understand the adhesion properties of shale oil/gas present in an acidic environment,which have great significance in unconventional resources development.

Self-healing elastomer modified proppants for proppant flowback control in hydraulic fracturing

To address proppant flowback issues during post-fracturing treatments and production,self-healing elastomer modified proppants(SMPs)are proposed.Owing to their inherent self-aggregation behavior,the SMPs can aggregate together spontaneously to prevent proppant flowback and increase the pack porosity.It is noteworthy that the SMPs have a firm and dry self-healing elastomer(SE)coating,making their storage,transport and use as conventional proppants possible.The SE synthesized through polymerization is rich in amidogens and carbonyl groups as characterized by Fourier transform infrared spectroscopy and the proton nuclear magnetic resonance.Thermal and thermomechanical properties of the SE coating are revealed by the thermogravimetric analysis,the differential scanning calorimetry and the rheological tests.The self-aggregation behavior of the SMPs is demonstrated by the adhesion force tests.The reversible hydrogen bonding interactions in SE coating contribute to the self-aggregation behavior of the SMPs,which is revealed by the thixotropy test and the FTIR analysis at different temperatures.With the self-aggregation behavior,the crushed proppants can aggregate in situ to form a stable structure again and therefore reduce the threat of narrowing down the fracture and proppant flowback,which has an important practical significance during oil and gas production.

Effects of Substrate Hydrophobicity/Hydrophilicity on Height Measurement of Individual DNA Molecules

Effects of substrate hydrophobicity/hydrophilicity on height measurement of individual ds-DNA molecules are investigated with tapping mode atomic force microscopy （TMAFM） and vibrating mode scanning polarization force microscopy （VSPFM）. The measured heights of ds-DNA on hydrophobic highly oriented pyrolytic graphite （HOPG） are remarkably less than those on hydrophilic bare mica and Ni^2＋ treated mica in both TMAFM and VSPFM. By analysing the results, we propose that the hydrophobicity/hydrophilicity of substrate can greatly influence the height measurement of DNA molecules.

Silver Film Growth on Glass Ceramic by Radio Frequency Magnetron Sputtering

Thin silver films are deposited by radio frequency magnetron sputtering on glass ceramic at room temperature.Variations of sputtering power,bios voltage and power density are carried out for each deposition,then parts of as-deposited samples are subjected to annealing at 600 ℃ within a vacuum chamber.Structural properties are studied by X-ray diffraction(XRD),scanning electron microscope(SEM)and laser scanning confocal microscope(LSCM).It is shown that structural properties have a strong dependency on sputtering power and annealing temperature.Electrical contact resistance measured by a four point probe instrument is directly affected by the thickness of films.It is also found that the film conductivity,especially in thinner films,is improved by the increasing grain size.Finally,the film adhesion is observed by scratch tests.And the adhesive ability deposited by radio frequency magnetron sputtering shows a better performance than that produced by traditional methods.

Analysis of Mechanical Adhesion Climbing Robot Design for Wind Tower Inspection

Maintenance of wind turbine farms is a huge task,with associated significant risks and potential hazard to the safety and well-being of people who are responsible for carrying the tower inspection tasks.Periodic inspections are required for wind turbine tower to ensure that the wind turbines are in full working order,with no signs of potential failure.Therefore,the development of an automated wind tower inspection system has been very cnucial for the overall performance of the renewable wind power generation industry.In order to determine the life span of the tower,an investigation of robot design is discussed in this paper.It presents how a mechanical spring-loaded climbing robot can be designed and constructed to climb and rotate 360°around the tower.An adjustable circular shape robot is designed that allows the device to fit in different diameters of the wind generator tower.The rotational module is designed to allow the wheels to rotate and be able to go in a circular motion.The design further incorporates a suspension that allows the robot to go through any obstacle.This paper also presents a finite element spring stress analy sis and Simulink control system model to find the optimal parameters that are required for the wind tower climbing robot.

Investigation on the adhesive contact and electrical performance for triboelectric nanogenerator considering polymer viscoelasticity

The triboelectric nanogenerator(TENG)is a new mechanical energy harvesting technology in which the typical viscoelastic material polydimethylsiloxane(PDMS)is widely used.Micro-/nano-textures are often fabricated on the PDMS surface to enhance the electrical performance of TENG.As the contact region decreases to micro/nano scale,the adhesive forces become dominant.However,there is still a lack of contact mechanics model considering both material viscoelasticity and the adhesive forces to guide the surface texture design.In this paper,the explicit data-fitting formulas based on the fractional derivative Zener model are firstly derived to identify the viscoelastic constitutive parameters,which can not only avoid the influence of the initial contact point,but also ensure the accurate conversion between the creep compliance and the relaxation modulus function.Then a viscoelastic-adhesive contact model based on the fitted constitutive parameters is established,and the numerical algorithms such as bi-conjugate stabilized(Bi-CGSTAB)method and fast Fourier transform(FFT)technique are employed to analyze the effects of material viscoelasticity and texture sizes on the contact and electrical performance.It is shown that,compared with results from the elastic-adhesive contact model,the contact area ratio based on the viscoelastic-adhesive contact model is significantly larger,which is much closer to the experimental results.Among the selected sizes of pyramid texture,the higher electrical performance can be obtained from the textures with a smaller pitch and a larger width under the heavier applied load.This study can provide a theoretical reference for the design of viscoelastic surface texture of TENG.

MEASUREMENT OF ADHESION FORCES IN AIR WITH THE VIBRATION METHOD

The vibration method represents a practical method for the measurement of adhesion forces and adhesion force distributions. This method causes sinusoidally alternating stresses and yields detachment and contact forces between particles and substrate of the same order of magnitude. Alternating contact forces of the vibration method can cause an adhesion force intensification through flattening of asperities. The measuring principle of the vibration method and the analysis of experimental results are described in the article. Normal adhesion forces (pull-off forces) are measured using the vibration method and the colloidal probe technique. The results of both methods show good agreement for small particle sizes. The influence of the detachment force direction is shown by comparing tangential and normal adhesion forces measured using particle reentrainment in a turbulent air flow and the vibration method, respectively. The surface roughness of the substrate and the relative humidity are shown to significantly influence the measured adhesion forces. For the calculation of the adhesion forces, an approach by Rabinovich was combined with approximations of plastic micro asperity flattening. The Rabinovich approach accounts for roughness effects on the van der Waals force by incorporating the rms roughness of the interacting surfaces, rms-values of the particles and substrates were measured with atomic force microscopy at different scanning areas.