High Adhesive Force Research Articles

Change of Characterization and Film Morphology Based on Acrylic Pressure Sensitive Adhesives by Hydrophilic Derivative Ratio.

Hydrophilic acrylic pressure-sensitive adhesives (PSAs) were synthesized by controlling the contents of 2-ethylhexyl acrylate (EHA), isobornyl acrylate (IBOA), and 2-hydroxyethyl acrylate (HEA); especially, the characteristic change of the HEA content was analyzed. Surface contact angle of acrylic PSA film decreased from 77.87° to 70.23° in the case of Acryl-2 to Acryl-8 (below HEA 10 wt %). However, the surface contact angle of Acryl-10 to Acryl-40 (HEA 10 wt % to 40 wt %) increased up to 92.29°, indicating hydrophobicity. All acrylic PSA films showed high adhesive force above 1800 gf/25 mm. According to X-ray diffraction (XRD) measurement, hydrophilic acrylic PSAs exhibited amorphous property and it was confirmed that the morphology of acrylic PSA film was significantly affected by the flexibility of the polymer chain and the strength of hydrogen bonding. The affinity with hydrophilic materials for acrylic PSA films was evaluated by T-type peel test, confirming that the affinity with hydrophilic materials is determined by the hydrophilicity of the acrylic PSA film. The synthesized acrylic PSA film is non-toxic regardless of the hydrophilicity.

Wear and Adhesion Properties of High-Pressure Torsion Processed Carbon Steel

High-pressure torsion (HPT) is one of the most promising methods employed to fabricate ultra-fine grained (UFG) materials for use in industrial applications. The aim of this work is to investigate the tribological behavior of UFG carbon steels produced by an HPT. In cases where the counter ball material was tungsten and cobalt cemented carbide (WC-Co), the wear rate (0.2~2.0x10-7 mm2/N) decreased with increasing the Vickers hardness (Hv200~650) for both HPT processed and quenched-tempered (QT) steels. On the other hand, in cases where the counter ball material was high carbon-chromium bearing steel (SUJ2), the wear rate of HPT (1.0~2.5x10-6 mm2/N) increased with increasing the hardness, which was an abnormal wear behavior. There was a tendency that the wear rate increased with an increase of the coefficient of friction, and that the coefficient of friction of HPT was 13-18 % higher than that of QT. Moreover, the adhesion force of HPT was 6-7 times higher than that of QT. Thus we have concluded that the high wear rate of HPT steels in the case of the SUJ2 ball wear tests were due to the high coefficient of friction as a result of the high adhesion force, which was caused by the high density of the grain boundaries in the UFG materials.

Fabrication methods of dry adhesive with various shaped microsuction cups

Bio-inspired micro- and nanostructures are emerging as novel dry adhesives owing to their high aspect ratio micropillar structure, resulting in collective van der Waals attraction between the adhesive and the substrate. Specifically, gecko-inspired structures exhibit great adhesive properties on smooth surfaces; however, the pull-off strength of micropillars in gecko-inspired surfaces can be decreased by applying a preloading force. Therefore, octopus suckers or suction cup-like structures have been considered as alternative microstructures providing high adhesion force. The fabrication of both microsuckers and micropillar structures is complicated and requires sophisticated control of the microstructure using photolithography and sequential polymer-based replica molding. Therefore, in this study, a fabrication method for octopus-like and suction cup-like micropatterns on polymer matrix is suggested by simple replica molding using a single master wafer. The relationship between the total adhesion force and the effective surface area of micropatterns was established and calculated by summing the preloading force, the suction force in the normal direction, and the shear force induced by van der Waals attraction. The results of adhesion force measurement and the repeatability test show that the micropatches with square microholes have high adhesion force (16 N/cm2) and good repeatability of attachments/detachments over 100 cycles.

Air assisted impact of drops: The effect of surface wettability

The airflow assisted impact of water drops on surfaces with various wettabilities is studied to understand the effect of shear force and normal imposed pressure provided by the incident airflow. Results show that the maximum spreading factor increases with the impact Weber number for the drops impacting a hydrophilic surface. For other surfaces, the spreading increases with the airflow for a given Weber number. However, the factor is observed to suddenly decrease at higher Weber numbers and airflow and for the less wetting surfaces. For the hydrophilic surface, as the drop continues spread, higher adhesive force between the drop and surface causes the rim to become thinner. The shear force pushes the rim outward. As the wettability decreases, a deceleration is observed at the early stage of spreading, forming fingers and thicker rim at the last stage. The thicker rim causes the viscous dissipation to decrease suddenly for the highest Weber number and airflow tested. The thicker rim resists the drop to spread. Detachment of the satellite drops on a hydrophilic surface increases with the airflow since the shear force increases. The normal imposed pressure applies pressure on the fingers and gives momentum to the lamella in the radial direction. A comparison of the measured maximum spreading with the one obtained from an existing model, is provided. Better comparison is found for the cases of less wetting surfaces, whereas good comparison is observed only at higher impact Weber numbers for the hydrophilic surface.

Mechanical properties and friction−wear characteristics of VN/Ag multilayer coatings with heterogeneous and transition interfaces

Abstract The heterogeneous multilayer interface of VN/Ag coatings and transition multilayer interface of VN/Ag coatings were prepared on Inconel 781 and Si(100), and the microstructures, mechanical and tribological properties were investigated from 25 to 700 °C. The results showed that the surface roughness and average grain size of VN/Ag coatings with transition multilayer interface are obviously larger than those of VN/Ag coatings with heterogeneous multilayer interface. The coatings with transition multilayer interface have higher adhesion force and hardness than the coatings with heterogeneous multilayer interface, and both coatings can effectively restrict the initiation and propagation of microcracks. Both coatings have excellent self-adaptive lubricating properties with a decrease of friction coefficient as the temperature increases, but their wear rates reveal a drastic increase. The phase composition of the worn area of both coatings was investigated, which indicates that a smooth Ag, Magneli phase (V2O5) and bimetallic oxides (Ag3VO4 and AgVO3) can be responsible to the excellent lubricity of both coatings. To sum up, the coatings with transition multilayer interface have excellent adaptive lubricating properties and can properly control the diffusion rate and release rate of the lubricating phase, indicating that they have great potential in solving the problem of friction and wear of mechanical parts.

Real-time monitoring the spatial distribution of organic fouling using fluorescence imaging technique

Many studies have demonstrated a close relationship between fouling and fluid dynamics to control fouling formation. However, few have been carried out to validate the relationship in practice, owing to the lack of techniques to evaluate fouling with hydrodynamics. We investigated the organic fouling of humic acid (HA) and tannic acid (TA) at three crossflow velocities using a fluorescence-labelled organism bioimaging instrument (FOBI). Higher crossflow velocity generally enhanced filtration performance; however, the type of foulants induced different fouling formation patterns on the membrane. The monitoring system and computational model revealed that HA fouling had strong (R2 = 0.82) correlation with the shear rate (obtained from a velocity of 10.42 cm/s), while TA had weak correlation (R2 = 0.13). HA fouling showed a high correlation with velocity profile at 10 cm/s, but TA fouling occurred in the over 20 cm/s velocity zone. This is because TA had relatively high adhesive force acting to the membrane, resulting in irreversible fouling that was hardly mitigated by crossflow control. Therefore, this study demonstrated that fouling development was predominantly controlled by hydrodynamic conditions, but the actual fouling distribution could be influenced by the physicochemical properties of dissolved organic matters.

Multifunctional mandibles of ants: Variation in gripping behavior facilitated by specific microstructures and kinematics

The elongated mandibles of certain ant species are dexterous grippers that can output a wide range of forces as needed for various tasks. Our combined experimental and theoretical research reveals the multifunctionality of the mandibles of Harpegnathos venator that is facilitated by specific microstructures and characteristic kinematics. First, we found that H. venator can pull off a spider’s (Heteropoda venatoria) leg by closing its long mandibles. We observed that the ant usually clamps the spider’s leg using the distal or middle part of its mandibles. In contrast, the ant can grip its egg with the proximal parts of its mandibles without causing damage. Our results showed that the spider’s legs are always fractured at the coxa-trochanteral joint. Second, we found that the force required to fracture the spider’s leg can be up to 500 times the ant’s body weight. On the other hand, the maximum force can be controlled to less than 2×10- 6N while gripping an egg. By combining microstructure imaging, kinematic tracking and mathematical modeling, we uncovered that the sharp teeth and dense bristles on the internal side of the mandibles determine the high adhesion force, while the concave teeth and biaxial rotation of the mandibles facilitate gentle gripping. We validated our findings by constructing an artificial mandible pair. This work expands the knowledge of the physiological multifunctionality in ant mandibles, and provides novel ways to reveal the multifunctionality in insect appendages by applying the tools of mechanical analysis and related experimental devices.

Synthesis, structure, and properties of the high Nb–TiAl alloy after Ni coatings by plasma surface alloying technique

Ni coatings were prepared on the high Nb–TiAl alloy by the plasma surface alloying technique. The results found that surface morphology and microstructure exhibited a strong dependence on the deposited temperature. The elements diffusion during the metalizing stage leaded to the high hardness value and adhesion force between the Ni coating and substrate. The corrosion resistance of the Ni-coated specimens depended on the fabrication temperature related to the deposition and diffusion layers. For the oxidation, the weight gain rate was involved in the chemical reaction in the initial oxidation stage. The inter-diffusion among elements such as the nickel, titanium, and aluminum resulted in the high adhesion force after the oxidation, improving the bonding force between the Ni coating and substrate.

Local experimental methodology for the study of microparticles resuspension in ventilated duct during fan acceleration

The purpose of this study is to develop an experimental methodology with relevant space and time resolutions to track the velocity properties responsible for the resuspension of microparticles during the acceleration stage of a fan start. Microparticles release is investigated over a time period of several seconds, i.e. at short time. This methodology involves velocity signal measurements thanks to Hot Wire Anemometry, and an optical counting method to build resuspension kinetics curves. During the fan acceleration the velocity evolution is characterized by two stages: a first increase without fluctuations, and then the acceleration with fluctuations. The same behavior is observed whatever the distance to the wall at which velocity is considered. The resuspension phenomenon seems to be initiated by a threshold turbulent kinetic energy, i.e. by turbulent events powerful enough to release microparticles having the lowest adhesion forces. For the studied particles properties/wall properties/aeraulic conditions, a significant fraction of particles remains on the duct wall at the end of experiments, despite the fact that the remaining fraction is stabilized. This may reveal that the highest energy levels of flow events seen by microparticles were not powerful enough to release particles having the highest adhesion forces.

Another look at the role of trapped air in cell adhesion on superhydrophobic materials

Superhydrophobic materials have been widely applied in biomedical applications because of their ability to resist proteins/cells. But controversial results exist as some researches demonstrated enhanced cell adhesion on superhydrophobic materials and trapped air at the solid–liquid interface has been deemed to resist cell adhesion. However to date, the difficulty of keeping the solid–liquid interface from adsorbing air after air elimination hinders our understanding of the role of air in cell adhesion. To directly compare cell behavior on superhydrophobic materials with and without trapped air, an O-ring was fixed on the sample by metal paper clip and a certain amount of buffer was maintained on the surface after trapped air was removed by ultrasonication. The results revealed that the adsorption of BSA and serum proteins on superhydrophobic TiO2 nanopores (TNPs) only slightly increased when air was eliminated. There is no discernible difference in cell adhesion on superhydrophobic TNPs with and without trapped air, whereas cell adhesion was enhanced when basal media were utilized to replace serum-containing media. It implies that trapped air does not necessarily inhibit cell adhesion, whereas serum proteins dominate cell adhesion on superhydrophobic TNPs. The possible reason why air has no significant effect on cell adhesion is that the high adhesion force of superhydrophobic TNPs enables intimate contact of cell with the top of superhydrophobic TNPs and diminishes the effect of air inside naoporous structure.

Hydrosilane-Modified Poly(2-Hydroxyethyl Methacrylate) Brush as a Nanoadhesive for Efficient Silicone Bonding.

Leaching of chemicals from adhesion promoters is, in particular, problematic for the food, water, pharmaceutical, and MedTech industries where any chemical contamination is unacceptable. A solution to this issue is to employ covalently attached nanoscale polymer brushes as adhesive layers for plastics. One of the industrially most relevant adhesion targets in that respect is poly(dimethylsiloxane) (PDMS), being used for many high-end applications such as catheters and breast implants. In this work, we have synthesized a novel surface-immobilized poly(2-hydroxyethyl methacrylate)-based brush adhesive containing reactive hydrosilane groups that can bond directly to PDMS. Two different medical grades of addition-cured PDMS were molded on top of titanium substrates already coated with the polymer brush. Titanium plates were used for the chemical analysis, and titanium rods were used for adhesion testing. Adhesion testing revealed a high adhesive force, in which cohesive failure was observed in the bulk PDMS. The necessity of the hydrosilane group in the polymer brush adhesive layer was demonstrated in comparative studies using similar brushes lacking this functionality.

Corrosion Resistance of ZnO Nanorod Superhydrophobic Coatings with Rose Petal Effect or Lotus Leaf Effect.

Superhydrophobic ZnO nanorods coatings with a strong adhesive force to the surface (rose petal effect) or a low sliding angle (lotus leaf effect) were fabricated on the zinc plate by the hydrothermal plus sol-gel method. The corrosion resistance and durability of the superhydrophobic coatings in 5 wt% NaCl solution were investigated. The coating with loose ZnO nanostructure on ZnO nanorods shows a high adhesive force to water with low corrosion resistance, while the coating with a layer of dense nanotubes on nanorods exhibits a low adhesive to water with a high corrosion resistance due to a layer of trapped air among micro/nanostructures, which can delay the penetration of corrosive media. It can be found that the nanorods coating with lotus leaf effect lost its superhydrophobicity after 5150 s immersion in salt solution and the water repellency model is transformed from Cassie state to Wenzel state.

Sustainable micro-manufacturing of superhydrophobic surface on ultrafine-grained pure aluminum substrate combining micro-embossing and surface modification

A hybrid process combining hot micro-embossing process with subsequent surface modification was proposed to realize an economic, environmental-friendliness and reusable sustainable production of superhydrophobic surfaces on ultrafine-grained (UFG) pure aluminum substrate. Hot micro-embossing was executed using a silicon die at 523 K with the force of 4.5 kN, where an array of micro hexagonal pillar patterns was formed with feature side length ranging from 75 μm to 165 μm. The embossed micro array structures were clearly printed well, with a good geometric transitivity and no obvious disfigurement. After surface modification, the water contact angle of the embossed surface, following by immersed in boiling water with micro/nano hierarchical structures, reached ∼160° which increased by 142% compared with original UFG pure aluminum. Moreover, the mechanism of the obtained superhydrophobic surface with high adhesive force was analyzed, which would be attributed to the Cassie impregnating wetting regime. The research indicates that there is a potential application by using hot micro-embossing process in the mass and sustainable production of superhydrophobic surfaces with excellent adhesive property without pollution.

Wetting Behavior and Maximum Retention of Aqueous Surfactant Solutions on Tea Leaves.

In this research, the maximum retention and wetting behavior of surfactant solutions (N-200, N-300, Tween-80, Morwet EFW, DTAB, SDS) on the surfaces of tea leaves was investigated based on surface free energy, surface tension, the contact angle, adhesion work, and adhesion force. The results showed that the contact angles of all surfactant solutions were kept constant with low adsorption at the tea leaf–liquid interfaces below 0.005%. With an increase in concentration, the contact angle of Tween-80 decreased sharply because the adsorption of molecules at the solid–liquid interfaces (ΓSL’) was several times greater than that at the liquid–air interfaces (ΓLV). Adhesion work decreased sharply and then reached a minimum at the critical micelle concentration (CMC), but then increased until reaching a constant. Moreover, a high adhesion force did not indicate better wettability, as it does with rose petals and peanut leaves. For tea leaf surfaces, an increase in the contact angle brought about an increase in the adhesion force. In addition, the maximum retention for Morwet EFW is at different concentrations compared to N-200, N-300, Tween-80, DTAB, and SDS, where the maximum retention of Morwet EFW on tea leaves was 6.05 mg/cm2 at 0.005%.According to the mechanisms of wetting behavior on plant surfaces, a recipe for pesticide formulation can be adjusted with better wettability to reduce loss, improve utilization efficiency, and alleviate adverse effects on the environment.

Influence of Endodontic Procedure on the Adherence of Enterococcus faecalis

IntroductionThe purpose of this study was to investigate the effects of instrumentation and irrigation on the initial adherence of Enterococcus faecalis to root canal dentin and to explore initial microbial adhesion to root filling materials. MethodsThe following specimens were prepared: instrumented and uninstrumented dentin, dentin treated with different irrigation protocols, and root filling materials. The number of E. faecalis cells adhered on dentin was measured. The adhesion force of E. faecalis cells on different materials and the roughness of different surfaces were measured. The contact angle of the surfaces was recorded. The results were analyzed using the t test. ResultsInstrumented dentin specimens had a significantly higher amount of E. faecalis adherence than uninstrumented dentin. There were higher numbers of adhering bacteria on the dentin when EDTA was used alone (P < .05) compared with other irrigants alone. The use of chlorhexidine (CHX) as the last irrigant for a certain time resulted in a reduced number of adhering bacteria when the specimens were first exposed to sodium hypochlorite (NaOCl) followed by EDTA. EDTA used alone had the highest adhesion force followed by NaOCl alone and CHX alone (P < .05). Dentin treated with EDTA alone had the highest roughness and contact angle followed by NaOCl alone and CHX alone (P < .05). CHX added as the final irrigant after NaOCl with EDTA irrigation reduced the contact angle (P < .05). Larger amounts of adhering bacteria and higher adhesion force were detected on the surface of gutta-percha and sealer than on the dentin surface (P < .05). ConclusionsInstrumentation and irrigation alter the initial adherence of E. faecalis to root canal dentin and the surface properties of the dentin as well.

Enhanced Directional Adhesion Behavior of Mushroom-Shaped Microline Arrays

We report directional switchable adhesion behavior inspired by the locomotion mechanism of gecko lizard. The robust mushroom-like polydimethylsiloxane microline arrays are fabricated by using silicon based over-etching process and replica molding. The line gecko patterns attached to the glass substrate exhibit strong shear adhesion forces in parallel and perpendicular directions with respect to the line direction and high adhesion hysteresis property only in the parallel direction. We have explained the directional adhesion behavior of the line gecko pattern by comparing peeling propagation and normal adhesion phenomenon. Then, we have successfully demonstrated silicon wafer transportation with the line gecko pattern by using directional adhesion behavior of the pattern, which is high shear adhesion force and low peeling force in the parallel direction with respect to the line direction.

Fabrication of superhydrophobic surfaces with tunable water droplet adhesion force by a two-step method

Abstract In this paper, we present a convenient approach to prepare hierarchical structured superhydrophobic coatings with tunable adhesion force, composed of micro-size glass beads, nano-size SiO2 particles and epoxy resin. Surfaces of two types with different roughness were fabricated, one type is only with single-scale roughness demonstrating lotus effect with low sliding angle, the other type is hierarchically micro-nano-structured roughness exhibiting petal effect with high adhesion force. The surface roughness is pivotal for controlling the wetting behavior and regulating the contact angle including the contact angle hysteresis. Varying the density of micro-size glass beads could adjust the roughness of the surface, which means the adhesion force of the prepared surface could be easily controlled based on the proposed method. Through variation of glass beads’ amount, the surface could be designed to pin the water droplet with different adhesion force when the surface turned upside down. The surface wettability, surface morphology, adhesion force of the prepared samples are investigated and mechanism of the Cassie-to-Wenzel state transition are discussed in detail. Furthermore, the convenient method provides a possibility for controlling surface morphology, composition and corresponding surface adhesion which could be applied to various substrates such as tile, wood, steel and fabric.

Carboxymethyl Cellulose Binder Greatly Stabilizes Porous Hollow Carbon Submicrospheres in Capacitive K-Ion Storage.

On account of the large radius of K-ions, the electrodes can suffer huge deformation during K-ion insertion and extraction processes. In our work, we unveil the impact of using carboxymethyl cellulose (CMC) instead of poly(vinylidene fluoride) (PVDF) as binders for K-ion storage. Our porous hollow carbon submicrosphere anodes using the CMC binder exhibit a reversible capacity of 208 mA h g-1 after 50 cycles at 50 mA g-1, and even at a high current density of 1 A g-1, they achieve a reversible capacity of 111 mA h g-1 over 3000 cycles with almost no decay, demonstrating remarkably improved reversibility and cycling stability than those using PVDF (18 mA h g-1 after 3000 cycles at 1 A g-1). It is showed that the CMC binder can result in higher adhesion force and better mechanical performance than the PVDF binder, which can restrain the crack during a potassiation/depotassiation process. According to the test of adhesion force, the hollow carbon submicrospheres using the CMC binder show above three times of average adhesion force than that using the PVDF binder. Furthermore, based on the rational design, our hollow carbon submicrospheres also exhibit 62.3% specific capacity contribution below 0.5 V vs K/K+ region, which is helpful to design the full cell with high energy density. We believe that our work will highlight the binder effect to improve the K-ion storage performance.

10-MDP Based Dental Adhesives: Adhesive Interface Characterization and Adhesive Stability-A Systematic Review.

The incorporation of functional monomers in dental adhesive systems promotes chemical interaction with dental substrates, resulting in higher adhesion forces when compared to micromechanical adhesion only. The 10-MDP monomer, whose chemical structure allows for a polar behavior which is favorable to adhesion, also promotes the protection of collagen fibers through the formation of MDP-calcium salts. This systematic review aimed to characterize the interface created by 10-MDP containing adhesive systems through an evaluation of the following parameters: Formation of nano-layered structures, capacity to produce an acid-base resistant zone, and adhesion stability. The research was conducted using PubMed, Cochrane Library, Web of Science and Embase, limited to English, Spanish, and Portuguese articles. The research was done according to the PICO strategy. The 10-MDP monomer has the capacity to produce an acid-base resistant zone on the adhesive interface, which increases the response to acid-base challenges. The adhesion established by these systems is stable over time. To have the best of these adhesive solutions, a scrubbing technique must be used to apply the adhesive system on dental substrates, in order to improve monomers infiltration and to create a stable bond. Time must be given for the solution to infiltrate, hybridize and form the MDP-Ca, improving adhesive stability.

Influences of cellular characteristics and media properties on membrane microalgal harvesting: a comparative study using Scenedesmus acuminatus cultivated at a pilot scale

AbstractBACKGROUNDIn order to reveal the influence of cellular characteristics and media properties on membrane microalgal harvesting, changes in the cellular characteristics and media properties of Scenedesmus acuminatus culture contaminated by microzooplankton were characterized, and their influences on membrane harvesting were compared with the control culture. Cells and algogenic organic matter (AOM) in the contaminated and control cultures were fractionated to evaluate the membrane fouling potential.RESULTSThe contaminated culture had a 32% lower average flux than control culture. Both the fractionated cells and AOM in the contaminated culture with or without concentration adjustment had higher membrane fouling potentials. Microzooplankton contamination caused more cell aggregates and transparent exopolymer particles, which formed less permeable cake layer. Increased AOM in contaminated culture contained more carbohydrates and humic/fulvic acid‐like substances, which caused a 15.5‐fold higher adhesion force between AOM and the membrane surface, and thus resulted in higher flux declining rates and lower backwashing recovery rates.CONCLUSIONMicrozooplankton contamination caused the formation of cell aggregates and high concentration of AOM in S. acuminatus culture. AOM played a more important role than microalgal cells in flux declining and backwashing recovery. It is necessary to develop cultivation practice and culture pretreatment techniques to improve membrane harvesting efficiency. © 2019 Society of Chemical Industry