Large Adhesion Forces Research Articles

Peeling-induced interfacial roughness and charging for enhanced triboelectric power generation

To date, there have been a lot of efforts to enhance the conversion efficiency of triboelectric nanogenerators (TENGs) via physical and chemical modifications of the polymer surface. Herein, we report that a facile peeling of polymer from a substrate can enhance the triboelectric power output. The peeling of spin-coated polydimethylsiloxane (PDMS) from glass and polytetrafluoroethylene (PTFE) substrates has revealed a considerable increase in interfacial roughness and lateral friction. Surface-sensitive X-ray photoemission spectroscopy and non-contact current measurements have also revealed the transfer of counter-material and interfacial charging. The surface roughness of peeled PDMS is significant for the PTFE substrate, while the surface charge is significant for the glass substrate. The triboelectric output power density for peeled PDMS from the substrate is similar, 10.3 µW/cm2, but significantly larger than that for as-grown PDMS (2.2 µW/cm2). The peeling strength of PDMS significantly increases for glass compared to PTFE after the oxygen plasma treatment of substrates. The triboelectric charge of peeled PDMS from a plasma-treated glass substrate is almost 1.3 times larger than that from a PTFE substrate. This work implies that peeling polymer from a rough substrate with a large adhesion force would be a facile and effective way to increase the triboelectric power output, without any delicate surface treatments.

Mechanical and failure behaviors of adhesively bonded dissimilar materials joints incorporating bio-inspired morphological irregularities

Adhesive dissimilar material joints between stainless steel grade 316L and polyethylene terephthalate glycol (PETG) plastic were examined, in which irregular interface morphologies inspired by natural sutures were incorporated. The joint interfaces exhibited various teeth-like, non-repetitive zigzag patterns based on a pseudo-randomization method and sutural interdigitation index. Effects of their irregularities on mechanical and failure characteristics of adhesive butt joints were studied by means of experiments and FE simulations. The cohesive zone model, Drucker-Prager plasticity model and ductile failure criterion were applied for the interface and PETG, respectively. Predicted load-displacement curves of joints with different teeth profiles were well validated. The degree of irregularity became higher to 20%, 40%, and 60%, the joint strengths decreased by 1.47%, 5.39%, and 11.95%, while the total energies to failure increased by 110.74%, 129.33%, and 161.23%, accordingly. More inhomogeneous morphologies led to earlier local damage initiation, but enhanced damage evolution range by impeding abrupt joint separation. Smaller teeth angles provided higher joint strength, whereas significant declines of bonding strength were observed by too acute teeth angle due to excessive stress localization and resulting teeth breakage. The teeth angle of 45º enabled the superior joint performance owing to a proper combination of interlocking and large adhesive force under shear stress state. Finally, a key insight for designing an optimal dissimilar joint with morphological irregularities was provided.

On the Adhesive Interaction Between Metals in Atomistic Simulations of Friction and Wear

Atomistic simulations are performed to assess how the main characteristics of a pairwise interatomic potential function can affect the occurrence of wear. A Morse-like potential is tailored in its attractive part such as to vary independently the cut-off radius and the maximum value of the attractive (adhesive) force. An ideal numerical experiment is then performed where the interaction between a metal crystal and a probe changes, while their material properties are not affected, to isolate the behavior of the interface. Force functions with larger adhesive force can loosely be interpreted as describing dry contacts while those with smaller adhesive force can be interpreted as describing lubricated contacts. Results demonstrate that the occurrence of wear is strongly dependent on the shape of the interatomic force field, and more specifically on the combination of maximum adhesive force and effective length of the interatomic attraction. Wear can initiate also at small adhesive energy, provided that the maximum adhesive force between atoms is large. When the surface of the crystal is taken to be rough instead of flat, the effect of the interatomic potential function on friction and wear becomes smaller, as the atoms belonging to the roughness are weakly bound to the rest of the crystal and are easily dislodged with any of the force functions we used.

Hitchhiker: A Quadrotor Aggressively Perching on a Moving Inclined Surface Using Compliant Suction Cup Gripper

Perching on the surface of moving objects, like vehicles, could extend the flight time and range of quadrotors. Suction cups are usually adopted for surface attachment due to their durability and large adhesive force. To seal on a surfaces, suction cups must be aligned with the surface and possess proper relative tangential velocity. However, quadrotors’ attitude and relative velocity errors would become significant when the object surface is moving and inclined. To address this problem, we proposed a real-time trajectory planning algorithm. The time-optimal aggressive trajectory is efficiently generated through multimodal search in a dynamic time-domain. The velocity errors relative to the moving surface are alleviated. To further adapt to the residual errors, we design a compliant gripper using self-sealing cups. Multiple cups in different directions are integrated into a wheel-like mechanism to increase the tolerance to attitude errors. The wheel mechanism also eliminates the requirement of matching the attitude and tangential velocity. Extensive tests are conducted to perch on static and moving surfaces at various inclinations. Results demonstrate that our proposed system enables a quadrotor to reliably perch on moving inclined surfaces (up to <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$1.07m/s$</tex-math> </inline-formula> and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$90^\circ$</tex-math> </inline-formula> ) with a success rate of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$70\%$</tex-math> </inline-formula> or higher. The efficacy of the trajectory planner is also validated. Our gripper has larger adaptability to attitude errors and tangential velocities than conventional suction cup grippers. The success rate increases by 45% in dynamic perches. <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Note to Practitioners</i> —This paper was motivated by the problem of perching on moving inclined surfaces using quadrotors. It can be used for perching on the various angled surfaces of an automobile to save energy and enlarge flight distance. It can also be exploited in air-ground cooperative tasks. In recent years, various grippers and trajectory planning methods have been devised to enable quadrotors to perch on static inclined surfaces. These strategies can not be used for perching on moving inclined surfaces. The task poses high requirements for the efficiency of trajectory planning and the grippers’ adaptability to pose errors. This paper proposes a real-time planning method to generate trajectories. The trajectories respect kinematic and motor lift constraints. They allow large attitude maneuvering of quadrotors. A multimodal search in a dynamic time-domain is developed to seek the minimum feasible time for the trajectory planner. Considering large pose errors in dynamic perching, a compliant gripper based on multiple independent suction cups is designed. The wheel and multidirectional layout of cups increase the adaptability to attitude and velocity errors. Results suggest that the proposed system is effective and reliable. In practice, our multiple cups would add weight penalty and increase the drag. The suction cups should be placed close to a quadrotor’s central axis to reduce the drag and disturbance in flow. The proposed system relies on an external motion capture system. In future research, we will focus on onboard sensing and control methods to achieve perching on moving inclined surfaces outdoors.

Dynamic traction force in trabecular meshwork cells: A 2D culture model for normal and glaucomatous states

Glaucoma, which is associated with intraocular pressure (IOP) elevation, results in trabecular meshwork (TM) cellular dysfunction, leading to increased rigidity of the extracellular matrix (ECM), larger adhesion forces between the TM cells and ECM, and higher resistance to aqueous humor drainage. TM cells sense the mechanical forces due to IOP dynamic and apply multidimensional forces on the ECM. Recognizing the importance of cellular forces in modulating various cellular activities and development, this study is aimed to develop a 2D in vitro cell culture model to calculate the 3D, depth-dependent, dynamic traction forces, tensile/compressive/shear strain of the normal and glaucomatous human TM cells within a deformable polyacrylamide (PAM) gel substrate. Normal and glaucomatous human TM cells were isolated, cultured, and seeded on top of the PAM gel substrate with embedded FluoSpheres, spanning elastic moduli of 1.5 to 80 kPa. Sixteen-hour post-seeding live confocal microscopy in an incubator was conducted to Z-stack image the 3D displacement map of the FluoSpheres within the PAM gels. Combined with the known PAM gel stiffness, we ascertained the 3D traction forces in the gel. Our results revealed meaningfully larger traction forces in the glaucomatous TM cells compared to the normal TM cells, reaching depths greater than 10-µm in the PAM gel substrate. Stress fibers in TM cells increased with gel rigidity, but diminished when stiffness rose from 20 to 80 kPa. The developed 2D cell culture model aids in understanding how altered mechanical properties in glaucoma impact TM cell behavior and aqueous humor outflow resistance. Statement of significanceGlaucoma, a leading cause of irreversible blindness, is intricately linked to elevated intraocular pressures and their subsequent cellular effects. The trabecular meshwork plays a pivotal role in this mechanism, particularly its interaction with the extracellular matrix. This research unveils an advanced 2D in vitro cell culture model that intricately maps the complex 3D forces exerted by trabecular meshwork cells on the extracellular matrix, offering unparalleled insights into the cellular biomechanics at play in both healthy and glaucomatous eyes. By discerning the changes in these forces across varying substrate stiffness levels, we bridge the gap in understanding between cellular mechanobiology and the onset of glaucoma. The findings stand as a beacon for potential therapeutic avenues, emphasizing the gravity of cellular/extracellular matrix interactions in glaucoma's pathogenesis and setting the stage for targeted interventions in its early stages.

Preparation and properties of alcohol‐resistant thermal transfer printing inks for multifunctional label printing via physical blending of resins

AbstractDue to the rise of the logistics industry and the widespread use of ink labels, problems such as the narrow operating temperature range of ink, poor alcohol resistance, and insufficient scratch resistance need to be solved urgently. In this work, creates alcohol‐resistant thermal transfer inks by mixing polypropylene chloride (VP‐365) and epoxidized hydrogenated bisphenol A (P) resin and incorporating them into the ink formulation. The synthetic ink has a lower glass transition temperature (118.2°C), allowing the ink to print at lower temperatures. It has small wetting angles (68°, 63°, 58°, 46°, and 40°) and a large adhesion force (10.44 – 14.4 N) for different labels. Further, to evaluate the printing performance of the ink, the ink was scratched under 1000 g pressure and in the environment of isopropyl alcohol to evaluate its printing performance. The produced ink has high scratch resistance (300 times) and good alcohol resistance (140 times). Moreover, the developed ink showed good printability, printing media versatility, high adhesion, and excellent alcohol resistance. The synthesis method is facile and cost‐effective, which paves a novel way towards high‐performance ink printing and thermal transfer technology industries.

Stretchable Strain Sensor with Small but Sufficient Adhesion to Skin.

Stretchable strain sensors that use a liquid metal (eutectic gallium-indium alloy; E-GaIn) and flexible silicone rubber (Ecoflex) as the support and adhesive layers, respectively, are demonstrated. The flexibility of Ecoflex and the deformability of E-GaIn enable the sensors to be stretched by 100%. Ecoflex gel has sufficiently large adhesion force to skin, even though the adhesion force is smaller than that for commercially available adhesives. This enables the sensor to be used for non-invasive monitoring of human motion. The mechanical and electrical properties of the sensor are experimentally evaluated. The effectiveness of the proposed sensors is demonstrated by monitoring joint movements, facial expressions, and respiration.

Agile and versatile climbing on ferromagnetic surfaces with a quadrupedal robot.

A climbing robot that can rapidly move on diverse surfaces such as floors, walls, and ceilings will have an enlarged operational workspace compared with other terrestrial robots. However, the climbing skill of robots in such environments has been limited to low speeds or simple locomotion tasks. Here, we present an untethered quadrupedal climbing robot called MARVEL (magnetically adhesive robot for versatile and expeditious locomotion), capable of agile and versatile climbing locomotion in ferromagnetic environments. MARVEL excels over prior climbing robots in terms of climbing speed and ability to execute various motions. It demonstrates the fastest vertical and inverted walking speed, whereas its versatile locomotion ability enables the highest number of gaits and locomotion tasks. The key innovations are an integrated foot design using electropermanent magnets and magnetorheological elastomers that provide large adhesion and traction forces, torque control actuators, and a model predictive control framework adapted for stable climbing. In experiments, the robot achieved locomotion on ceilings and vertical walls up to 0.5 meter (1.51 body lengths) per second and 0.7 meter (2.12 body lengths) per second, respectively. Furthermore, the robot exhibited complex behaviors such as stepping over 10-centimeter-wide gaps; overcoming 5-centimeter-high obstacles; and making transitions between floors, walls, and ceilings. We also show that MARVEL could climb on a curved surface of a storage tank covered with up to 0.3-millimeter-thick paint with rust and dust.

Characterization of adhesivity of organic enriched sea spray aerosols by atomic force microscopy

Aerosol particles can trigger various environmental issues, not only when they are airborne but even after their deposition. For example, highly corrosive sea spray aerosols (SSA) can be deposited on surfaces and cause damage to steel- or concrete-based infrastructure, especially in coastal areas. However, the extent to which the adhesive behavior of SSA is affected by different degrees of organic mixing has not been sufficiently studied. The goal of this study was to evaluate the adhesion forces of both laboratory-generated and ambient SSA with a variety of organic contents on an individual particle basis using atomic force microscopy. Aerosols were also generated using a bulk sea foam sample collected from the coast of Noto Peninsula, Japan to simulate SSA enriched in a complex mixture of marine organics. The adhesion force of the sea foam particles was compared with that of two types of standard monosaccharides (glucose and fucose), artificial inorganic sea salt (ASS), glucose and ASS mixtures at different mass ratios, and ambient sea salt (SS) particles. Pure monosaccharide or its mixtures showed substantially larger adhesion forces than predominantly inorganic particles such as ASS and SS. In addition, it was found that a fraction of sea foam particles showed similarly large adhesion forces, suggesting that organic (e.g., monosaccharides)-enriched SSA can be considerably more adhesive than inorganic salts. Furthermore, a few but surprisingly adhesive particles were also identified among ambient aerosols. Therefore, it is necessary to consider the abundance of organics such as saccharides to correctly evaluate the adhesivity of SSA.

Fabrication of bionic hydrophobic micropillar arrays by femtosecond lasers for droplet manipulation

<p indent="0mm">Nature is the source of inspiration for human design and manufacture. The preparation of biomimetic functional surfaces is a hot research topic, especially in the preparation of biomimetic hydrophobic surfaces. Common preparation methods include plasma etching, lithography, and so on. But those preparation methods are complex. In this article, a simple strategy for the preparation of hydrophobic micropillar arrays is proposed based on femtosecond laser micro-nano fabrication and replica-mold technology, and the relationship between structural parameters, surface chemical modification, and wettability is systematically investigated. It was found that structural parameters, such as spacing, diameter, and height, had a large effect on the wettability of the chemically modified micropillar arrays. When the spacing of the micropillars increases from 400 to <sc>600 μm,</sc> the droplet sliding angle increases from 31° to 76°. This is because as the spacing increases, the droplets gradually penetrate the gaps between the micropillars. As the droplet slides across the surface, it creates a larger energy potential barrier, so the larger the spacing, the greater the sliding angle, which means the greater adhesion force on the surface. Similarly, when the diameter increases from 100 to <sc>300 μm,</sc> the droplet sliding angle increases from 40° to 80° accordingly. The contact area between the droplet and the micropillar array increases with increasing diameter, that is, the adhesion force between the droplet and the micropillar array increases gradually. Therefore, the sliding angle of the droplet is increased on a larger diameter micropillar array, i.e., the adhesion force is relatively high. The height of the micropillar also affects wettability. When the height is below <sc>100 μm,</sc> the droplet will fall into the structure under the action of its gravity, and contact with the substrate, resulting in a larger adhesion force. Even when the sample is turned over 90°, the droplets do not slip off. When the height is greater than <sc>200 μm,</sc> there is an air layer between the droplet and the substrate, which becomes increasingly visible as the height increases. The sliding angle of the droplet on the micropillar array maintains at ~50° and does not change significantly with increasing height. This is because the contact state between droplets and microcolumns will not be changed after the height increases to a certain extent (≥200 μm). Furthermore, the prepared samples exhibit excellent fatigue resistance. After testing, the maximum tensile rate of the sample can reach 400%, and the micropillar array can still recover to the original morphology. Based on the above experimental results, the surface adhesion force of the micropillar array can be controlled by adjusting the structural parameters, such as diameter and spacing. We designed a micropillar array with different spacings (400 and <sc>600 μm)</sc> to realize the control of droplet sliding behavior by using this property. In addition, the micropillar arrays with different spacings can be combined into specific patterns to realize the micro-reaction of droplets. This preparation method of biomimetic hydrophobic micropillar arrays is not only simple but also widely applicable. The prepared hydrophobic micropillar arrays have potential applications in microfluidic chips, biomedicine, and chemical micro-reactions.

Modeling and Analysis of Magnetic Adhesion Module for Wall-climbing Robot

Magnetic wall-climbing robots have wide applications due to their large adhesive force and loading capacity. However, researches have seldom focused on the magnet patterns and magnetic characteristics of the adhesive module, which may influence the output performance of the robot greatly. Therefore, the purpose of this study is to analyze the magnet array, flux distribution and magnetic adhesive force of wall-climbing robot in both quantitative and qualitative ways. It helps to improve the magnetic force and loading capacity significantly. The concept design of the wall-climbing robot is introduced and the system stability is analyzed. Following that, four magnet patterns are presented and the magnetic flux distribution is numerically simulated. The comparison among them shows that the alternatively magnetization pattern can generate larger magnetic flux density relatively. Subsequently, the magnetic field and adhesive force are both formulated analytically. It is worth noting that the curved surface is considered for the analytical modeling in this study. Thus, the modeling approach can be implemented to the magnetic characteristic analysis of other similar magnetic adhesive robots. Then, the numerical simulation is conducted on the magnetic field and force output to validate the analytical models. One research prototype of the magnetic wall-climbing robot is developed, and the system hardware architecture is introduced. Experiments are carried out to validate the analytical model and output performance of the robot system. The experimental result is consistent with the analytical model and numerical computation.

Characteristics of bio-CaCO3 from microbial bio-mineralization with different bacteria species

Nowadays, MICP (Microbially Induced Calcite Precipitation) technology has broad application prospects in civil engineering, such as sand consolidation, crack healing in cement-based materials, solid waste treatment, etc. Nevertheless, there were no systematic studies on the difference of bio-CaCO3 produced by different microbial strains. In this study, XRD, TEM, SEM, STA and AFM were used to investigate the differences in crystalline form, morphology, size, decomposition temperature, and adhesion force of mineralized products. Those products were produced by Photosynthetic bacteria, Bacillus mucilaginosus, Bacillus alcalophilus, Bacillus pasteurii and chemical pathway. The results showed that all four microbial pathways were more productive than the chemical pathway. The calcite crystals formed by the chemical pathway presented an oblique hexagonal lattice structure, while calcite crystals formed by four microbes presented a spherical or irregular polyhedral structure under the action of organic substrate. The calcite crystals formed by Bacillus pasteurii were smallest in size and those formed by Photosynthetic bacteria were the largest, and their crystalline sizes were smaller than that of calcite produced by chemical pathway. The decomposition temperature and adhesion force of chemical CaCO3 were lower than that of bio-CaCO3, with the highest decomposition temperature (765.80 ℃) and the largest adhesion force (68.91 nN) of calcite induced by Bacillus pasteurii.

Acarid Suction Cup‐Inspired Rapid and Tunable Magnetic Adhesion

AbstractAdhesion appears in nature as a kind of clinging strategy for living creatures to survive in a complex environment. Nevertheless, the artificial counterpart applications are limited by many factors, such as slow responding rate and high driving voltage. In this paper, a novel magnetic adhesion achieved by the actuation of Ecoflex embedded with iron particles is presented, which is demonstrated by a magnetic suction cup (MSC) that can switch the adhesion state within 500 ms. Compared with suction cups made of the dielectric elastomer in existing literature, the present work's driving voltage is safe for humans. Furthermore, a mechanical model is developed and verified to optimize the design of the MSCs. By applying an altering magnetic field, the adhesive force varying with time exhibits complex waveforms such as sinusoidal wave, triangle wave, square wave, and even pulse wave can be achieved. For some situations that large adhesion force is not necessarily considered while the adhesion requires to be accurately and quickly controlled, such as transfer printing and intelligent sensing, the magnetic adhesion demonstrated in this article will enrich the future available applications.

The Resistance of TiN Coatings to Solid Particle Erosion Using Different Deposition Methods

It was found that the corrosion resistance of WC was significantly improved with the addition of a TiN coating. Erosion testing was done using solid particles to quantify dynamic erosion processes in TiN-coated specimens. TiN coatings were deposited on different specimens using physical vapor deposition (PVD), chemical vapor deposition (CVD), or plasma chemical vapor deposition (PCVD). Results from the erosion tests indicated that the corrosion resistances of the WC-Co cemented carbide samples were improved following all three coating processes. The order of corrosion resistance in terms of strength was TiN-PVD > TiN-CVD > TiN-PCVD > uncoated specimen. The TiN-PVD sample also had the highest resistance to erosion of the three sample types. The principal factors that influence erosion resistance are adhesion forces and the ratio of the hardness (H) of a material to the elastic modulus (E) of the material. Experimental results from this study demonstrated that the TiN-PVD sample had a large adhesion force (42 N) and higher H/E and H3/E2 values relative to the other sample types.

Adaptive Aerial Grasping and Perching With Dual Elasticity Combined Suction Cup

To perch on or grasp the objective surface using the suction cup-based manipulator, the precise contact control is commonly required. Improper contact angle or insufficient contact force may cause failure. To enhance the tolerance to flight control insufficiency, a suction cup that comprises an inner soft cup and an outer firm cup to facilitate its engagement without reducing the adhesion stiffness is investigated. The soft cup is adaptable to the angular error induced by the multicopter and the resulting adhesion force can draw the firm cup and correct the angular error between the firm cup and the surface. These effects increase the engagement rate and reduce the dependence on precise control. The outer firm cup is devoted to providing a large adhesion force and a stiff base for subsequent tasks. To reduce the air evacuation time in the firm cup, a novel self-sealing structure is designed. Based on the combined cup, we build a multifunctional aerial manipulation system which can execute perching or lateral aerial grasping tasks. With the proposed prototype, the comparative flight experiments involving perching on a wall under disturbance and grasping an object are conducted. The results demonstrate that our proposed suction cup outperforms the conventional cup.

Thickness-dependent frictional behavior of topological insulator Bi2Se3 nanoplates

Two-dimensional Bi2Se3 TIs were recently found to be the most promising room-temperature topological insulators for its relatively large bulk gap, but its surface frictional response is little investigated. Here, we prepared single-crystalline Bi2Se3 nanoplates with a lateral dimension up to ~ 1 μm and a thickness of less than 200 nm via a simple polyol method, and the molecular structure and morphology were characterized in detail using different methods. The micro-frictional behavior of Bi2Se3 nanoplates with different thickness is inventively investigated with AFM technique. The atomic stick–slip friction stemming from periodic crystal lattice, and the larger friction force of thinner nanoplates is attributed to the larger adhesion force and enhanced energy dissipation. This work has, for the first time, built the link of the behavior of topological protected surface and mechanical friction behavior of Bi2Se3.

Adhesion-force micro-scale study of desiccating granular material

Experiments on five-, four-, three- and two-wet-hydrophilic-grain clusters were performed to investigate evolution of adhesion of granular media during drying on the micro-scale. The experiments show that the adhesion-force of a cluster initially grows at most to three times the original value before decreasing to zero by the end of evaporation. The adhesion-force is composed of capillary pressure force acting over the liquid/solid contact surface area, and surface tension forces acting over the three-phase contact perimeter length. This is in contrast with most macro-scale phenomenological models, in which the only desaturation process variables affecting strength are suction and saturation. Both the contact surface area and contact perimeter length are reduced to zero upon complete liquid evaporation. The morphology of an evaporating water body evolves through slow flow controlled by evaporation rate, interrupted by various modes of fast air entry, which are non-equilibrium jumps of liquid/gas interfaces (Haines jumps). The instabilities involve large adhesion force discontinuities and substantial water mass reconfiguration with water flow in an extremely short time, which makes the process transient. The reconfigurations can reduce the original multi-grain water clusters to four-, three- and two-grain clusters by way of three different instability modes: of thin-sheet instability, or meniscus snap-through instability, depending on the sign of the Gauss curvature of the liquid surface, or finally, for two-grain bridges only, a liquid wire pinch-off. For larger meso-scale assemblies, however, the global adhesion-force evolution is little affected by the jumps. The air entries are potential sites for drying cracks. The (approximately) calculated capillary pressure for two- and three-grain clusters, in no cases is seen to reach high values, predicted from water retention curves.

Abnormally large and small adhesion forces between plasma-treated silicon surfaces studied on AFM

ABSTRACT Surface hydrophilicity has a crucial effect on adhesion forces in air. However, the influence demands clarification. A spherical tip was used to measure adhesion forces on silicon samples with different treatment methods on an atomic force microscope at high relative humidity. The treatment methods were plasma treatment with storage for a time and ultrasonic cleaning in alcohol and water. Both abnormally large and small adhesion forces were observed, and the adhesion force behavior is closely related to surface hydrophilicity. With plasma treatment, the maximum force can be as large as ~4.8 μN, which was attributed to the formation of siloxane bonds (Si-O-Si) between opposing surfaces and the capillary force due to a water bridge. However, the abnormally large adhesion force can only last for a few hours, and then either decreases gradually or decreases suddenly to an abnormally small value. The decrease was attributed to the displacement of hydroxyl groups by organic molecules and the adsorption of some other airborne contaminants on the surface. The possible reasons for abnormally small forces were also presented. However, the abnormal values were not observed on samples with ultrasonic cleaning. These results may help facilitate the anti-adhesion design for silicon-based small-scale systems.

Promoting effect of water vapor on particle matter combustion in a low-temperature continuous regeneration type PM removal device using a fluidized bed

A fluidized bed type particulate matter (PM) removal device has been developed by focusing on the adhesion force under condition of non-water vapor. This device efficiently collects fine PM and can be operated as a low-temperature continuous regeneration device. The exhaust gas of a combustor includes water vapor at concentrations of 5–15 vol%. To further develop this device, the effect of water vapor on the continuous regeneration was investigated. The collection efficiency increases due to the water vapor. The reaction rate constant increases with increasing water vapor and with decreasing PM diameter. It is shown that water vapor promotes PM combustion at 250–400 °C. A smaller PM suits PM collection and combustion because smaller PM results in relatively larger adhesion force and well contacts the oxidant by dispersing it on the bed particles. The continuous regeneration temperature decreases to 380 °C due to the water vapor under optimal conditions.

Skin Layer Effects on Adhesion Forces of PVA Brushes and Its Temperature Dependence

In this study, the adhesion forces between PVA (PolyVinyl Acetal) brushes and solid surfaces were measured directly using a highly responsive load cell. The adhesion forces were compared based on contact time, and the influence of skin layer existence on PVA brush surface was investigated. In addition, the surface temperature dependence of the adhesion forces was also studied. Results showed that the adhesion force increased with increasing surface contact time. For a PMMA surface, significantly large adhesion forces were observed. It was also seen that the adhesion force decreased with increasing temperature. However, by using the present setup, the adhesion forces in all experimental conditions without skin layer brush cases could not be measured.