High Adhesive Force Research Articles

Effects of bulk viscoelasticity and surface wetting on the contact and adhesive properties of a soft material

Because of the wide practical applications of soft materials, the surface contact and adhesive behaviors need to be comprehensively understood. Here, we systematically investigated the effect of bulk viscoelasticity and surface wetting on the dynamic behavior of contact and adhesion of soft polydimethylsiloxane (PDMS) surfaces. Experimental results showed that during the indentation process, the relation between loads and contact radius were close to the Johnson-Kendall-Roberts (JKR) mode, but the load-penetration curves presented a roughly linear dependence with increasing preloads transferring from the JKR to Hertz mode; the detaching process exhibited a pronounced “stick-split” behavior, where the spherical probe first stuck to the soft PDMS without decreasing the contact area, and then the crack of the contact edge opened and split, providing high adhesive forces far exceeding the JKR prediction. The introduction of liquids between the probe and soft PDMS strongly decreased the contact area, reduced the stick time, and weakened the dry adhesive strength depending on the surface tension. The internal friction induced by the segmental motion of long-chain molecules and the interfacial resistance of liquid were suggested to be responsible for these phenomena.

Traction Force Measurements of Human Aortic Smooth Muscle Cells Reveal a Motor-Clutch Behavior

The contractile behavior of smooth muscle cells (SMCs) in the aorta is an important determinant of growth, remodeling, and homeostasis. However, quantitative values of SMC basal tone have never been characterized precisely on individual SMCs. Therefore, to address this lack, we developed an in vitro technique based on Traction Force Microscopy (TFM). Aortic SMCs from a human lineage at low passages (4-7) were cultured 2 days in conditions promoting the development of their contractile apparatus and seeded on hydrogels of varying elastic modulus (1, 4, 12 and 25 kPa) with embedded fluorescent microspheres. After complete adhesion, SMCs were artificially detached from the gel by trypsin treatment. The microbeads movement was tracked and the deformation fields were processed with a mechanical model, assuming linear elasticity, isotropic material, plane strain, to extract the traction forces formerly applied by individual SMCs on the gel. Two major interesting and original observations about SMC traction forces were deduced from the obtained results: 1. they are variable but driven by cell dynamics and show an exponential distribution, with 40% to 80% of traction forces in the range 0-10 µN. 2. They depend on the substrate stiffness: the fraction of adhesion forces below 10 µN tend to decrease when the substrate stiffness increases, whereas the fraction of higher adhesion forces increases. As these two aspects of cell adhesion (variability and stiffness dependence) and the distribution of their traction forces can be predicted by the probabilistic motor-clutch model, we conclude that this model could be applied to SMCs. Further studies will consider stimulated contractility and primary culture of cells extracted from aneurysmal human aortic tissue.

Circular economy in RFID technology: analysis of recycling methods of RFID tags

Circular Economy (CE) is one of the approaches which are intensively developed and tested in different areas of industry and services. The aim of this solution is to use many kinds of resources in a closed flow and to achieve as a small amount of waste as it is possible.One of the potential areas of using CE is Radio Frequency Identification (RFID). In RFID systems tags are utilized in various forms. This paper addresses investigation of a recycling process of RFID tags. Different attachment methods of these tags were tested and then, a recycling procedure was prepared based on the obtained results in which adhesives are recommended to be used as an attaching material between a tag and an identified object. The mentioned procedure was evaluated with using paper-face RFID tags. It was confirmed applicability of the proposed solution. Moreover, the conducted research revealed that an adhesion force of the adhesive layers in the prepared RFID tags decreased in the most extent during the first recycling cycle. It was found that in order to preserve a high adhesion force of these layers it is suggested to place the tags on a clean surface.

Interactions between apolar, basic and acidic model oils and a calcite surface

In this study, the atomic force microscopy colloidal probe technique was employed to investigate the interaction between apolar, basic and acidic model oil probes and a calcite surface in solutions containing different concentrations of NaCl, CaCl2 and Na2SO4. In the presence of SO42−, hydration and structural forces were observed between apolar model oil probes and a calcite surface on approach. Relatively low adhesion forces were observed between the basic model oil probes and the calcite surface, while higher adhesion forces were observed between the acidic model oil probes and the calcite surface. Furthermore, the adhesion forces between the basic model oil probes and the calcite surface significantly increased in the presence of SO42−, while the adhesion force between the acidic model oil probes and the calcite surface decreased in the presence of Ca2+ or SO42−. The differences in the adhesion forces are related to electrostatic attraction and ion bridging forces between the model oil probes and the calcite surface.

Start-up evaluations and biocarriers transfer from a trickling filter to a moving bed bioreactor for synthetic mariculture wastewater treatment

Mariculture wastewater treatment by nitrification requires a long start-up time due to high salinity stress. This study aimed to verify the faster start-up of a trickling filter (TF) compared to a moving bed bioreactor (MBBR) treating synthetic mariculture wastewater, and to investigate the feasibility of transferring mature biocarriers from the TF to a new MBBR (TF-MBBR). The nitrogen removal performance, biofilm physicochemical properties and microbial communities were investigated. The results obtained showed that, the TF started up 41 days faster than the MBBR, despite the richer microbial diversity in the latter. Lower biofilm roughness and protein content as well as higher adhesive force and polysaccharide content in the TF were obtained compared to the MBBR. Adhesive force was found to be negatively correlated with roughness (r = −0.630, p = 0.069). Transmittance assigned to amide II (1538 cm−1) and amid III (1243 cm−1) through Fourier transform infrared spectroscopy (FTIR) determination was only obtained in the TF, which was likely related to the faster start-up. Nitrosomonas and Nitrospira were detected as the predominant nitrifiers in both reactors. In addition, the new MBBR, incubated with the mature biocarriers transferred from the TF, had a satisfactory nitrification performance with no lag time. Interestingly, the transfer action increased the microbial diversity and made the biofilm physicochemical characteristics shift toward those of the MBBR. Taken together, the study confirmed that MBBR nitrification start-up can be accelerated via TF and biocarrier transfer.

Robust raspberry-like all-polymer particles for the construction of superhydrophobic surface with high water adhesive force

In this work, we present a simplified versatile approach to synthesize monodisperse and robust entirely polymeric raspberry-like particles (RPs) via an in situ seeded polymerization method. The RPs with dual-scale hierarchical structure were prepared by absorption of monomer styrene, cross-linkable monomer ethylene glycol dimethacrylate (EDGMA) and azobisisobutyronitrile (AIBN) initiator into hollow P(styrene–divinylbenzene-trifluoroethyl methacrylate) [P(S-DVB-TFEMA)] nanoreactors, and then massive corona polymeric P(S-EDGMA) particles were in situ grafted onto the core hollow P(S-DVB-TFEMA) from the inside out, obtaining the robust all-polymer P(S-DVB-TFEMA)@P(S-EDGMA) RPs. The prepared RPs possess excellent mechanical and chemical stability toward long-term ultrasonic and acid/base treatment. Without post-modifications, the particulate film assembled by the RPs exhibited the static contact angle of 154° and high adhesion to water droplets. Theoretical model of the RPs and theoretical analysis, which corresponded well to experimental data, further reveal the high adhesive phenomenon. More importantly, the prepared sticky superhydrophobic surface colored by fluorescent dye can be utilized as “a mechanical hand” for micro-droplet transportation with high visibility in UV dark chamber. Thus, we anticipate that the sticky superhydrophobic surface constructed by the robust all-polymer RPs will offer great potential applications in micro-droplet manipulation and biological detection.

Gradient structure based dual-robust superhydrophobic surfaces with high-adhesive force

Dual-robust (mechanical and chemical robust) superhydrophobic surfaces with a high adhesive state have aroused lots of attention for their potential application in liquid transportation, biochemical separation and in situ detection devices. Herein, we design a gradient structure based multi-scale micro- and nano-structures (inorganic-organic interpenetrating structures, self-similar sacrificial structures and micro-nano structures) to realize dual robust superhydrophobic surfaces by spraying method. Upon changing the fabrication process, three kinds of superhydrophobic surfaces were made based on benzoxazine, mesoporous SiO2 and imidazole. A rigorous sandpaper abrasion test, chemical resistance test (pH = 1–14, 12 h) and anticorrosion test were carried out to exhibit the environmental stability of the system. High adhesive properties of surfaces were demonstrated by adhering water test. The clear multi-scale structures are showed and its relationship with properties is built. Scanning electron microscope was used to examine different structures and the gradient structure in system. The gradient structure based dual-robust superhydrophobic surfaces give a promising prospect for water transportation application in their large-scale and low-cost fabrication method and super mechanical and chemical robust.

The analysis of adhesion force at the interface of gas diffusion layer and channel in polymer electrolyte membrane fuel cell

The adhesion force of water droplet on the gas diffusion layer (GDL) is modeled based on the droplet deformation. The deformed droplet is represented as an ovoid shape. The adhesion force is calculated based on it and verified by the surface tilting experiment. The model predicts the shape of deformed droplet and adhesion force within 30% error, whereas previous models predict adhesion force with error larger than 30%. The modified model is used to compare the adhesion force among 3 types of GDL having pore gradient. The comparison result is well matched with the water distribution in polymer electrolyte membrane fuel cell (PEMFC) and water detachment phenomena at the GDL. High adhesion force makes more water accumulation at the interface of GDL and gas supplying channel. This makes different boundary condition and changes the water distribution in PEMFC.

The characteristics of organic matter influence its interfacial interactions with MnO2 and catalytic oxidation processes

The influence of dissolved organic matter (DOM) properties on its interfacial interactions with MnO2 and on catalytic oxidation processes was studied by Time-Resolved Dynamic Light Scattering (TR-DLS) and Atomic Force Microscopy (AFM) under varied solution conditions. Four DOM fractions of different characteristics (e.g., SUVA, hydrophobic character, structural properties) were selected. Bared-MnO2 nanoparticles readily aggregated in NaCl and CaCl2 solutions. Classic DLVO Theory successfully described critical coagulation concentrations and aggregation behaviors. In NaCl solution, DOM adsorbed on MnO2 nanoparticles and provided electrosteric stabilization. The two DOM fractions of higher hydrophobic (HPO) character were more efficient in decreasing the aggregation rates. Enhanced MnO2 aggregation was observed at high Ca2+ concentrations due to charge screening and cation bridging between carboxyl groups in DOM structures. The addition of oxidant (H2O2) induced a high aggregation of bared-MnO2 nanoparticles, possibly due to the release of Mn2+ (i.e., complexation mechanisms) and generation of reactive species (O2−, HO2−, and H). Contrasted with their hydrophilic (HPI) counterparts, HPO isolates adsorbed on MnO2 significantly decreased the catalytic oxidation processes between H2O2/MnO2; suggesting a more efficient and stronger DOM coating. Interfacial forces measured by AFM, showed weaker interactions between HPI isolates and MnO2; suggesting unfavorable polar interactions. Conversely, the high adhesion forces between MnO2/HPO isolate would indicate stronger bonds and hydrophobic interactions. This study provided a nanoscale understanding of the impact of DOM characteristics on: a) performance of the MnO2 coated ceramic membranes in water treatment, and b) biogeochemical cycle of Mn-oxides in the environmental.

Glass-particle adhesion-force-distribution on clean (laboratory) and contaminated (outdoor) surfaces

This paper explores whether laboratory-clean samples are representative of real outdoor surfaces – often covered in dust and other contaminants – with respect to adhesion properties, which ultimately affect particle resuspension. In this study, Atomic Force Microscopy (AFM) was used to measure the adhesion force between a clean, smooth glass particle (5 µm in diameter) and two glass slides, one prepared according to common laboratory practices (hereafter, clean glass) and a second one left outdoors for six weeks (hereafter, contaminated glass). It was found that the adhesion force distribution was bimodal for the clean glass while it showed three peaks for the contaminated glass. For both surfaces, the adhesion force showed a peak at very low adhesion values (< 100 nN) representing 1.2% of the measurements for the clean glass and 58% for the contaminated glass. This low-adhesion peak is important because it represents the particles that would be resuspended first even in light winds. The low adhesion-force measurements were associated with the presence of contaminants on the surface. Another notable difference between the adhesion force distributions was a long tail at high adhesion forces for clean glass (up to ~1900 nN) and the absence of the tail for the contaminated glass, which had a maximum adhesion force of 950 nN. The mean adhesion force on the contaminated glass was also lower than on the clean glass (206 ± 240 nN vs. 516 ± 354 nN). These observations indicate that the adhesion force distribution between a 5-µm smooth and clean glass sphere and the outdoor contaminated glass surface is quite different from that of the clean glass surface. Hence, one should be cautious when using adhesion force measurements from clean surfaces to estimate particle resuspension from outdoor surfaces.

Optimisation of the Adhesion of Polypropylene-Based Materials during Extrusion-Based Additive Manufacturing.

Polypropylene (PP) parts produced by means of extrusion-based additive manufacturing, also known as fused filament fabrication, are prone to detaching from the build platform due to their strong tendency to shrink and warp. Apart from incorporating high volume fractions of fillers, one approach to mitigate this issue is to improve the adhesion between the first deposited layer and the build platform. However, a major challenge for PP is the lack of adhesion on standard platform materials, as well as a high risk of welding on PP-based platform materials. This study reports the material selection of build platform alternatives based on contact angle measurements. The adhesion forces, investigated by shear-off measurements, between PP-based filaments and the most promising platform material, an ultra-high-molecular-weight polyethylene (UHMW-PE), were optimised by a thorough parametric study. Higher adhesion forces were measured by increasing the platform and extrusion temperatures, increasing the flow rate and decreasing the thickness of the first layer. Apart from changes in printer settings, an increased surface roughness of the UHMW-PE platform led to a sufficient, weld-free adhesion for large-area parts of PP-based filaments, due to improved wetting, mechanical interlockings, and an increased surface area between the two materials in contact.

Facile design of “sticky” near superamphiphobic surfaces on highly porous substrate

Several “sticky” near superamphiphobic surfaces were fabricated on naturally porous and rough substrate by simply deposing oligoamides solutions, needless of surface modification or integrating nano-materials. These surfaces exhibit very high water and oil contact angles (CA) (water CA > 150°, oil CA > 140°) together with high sliding angles (>90°). The nanomaterial-free coating compounds are well-defined, homologous partially fluorinated oligoamides (synthesized via condensation reactions) which have consistent but slightly varied properties, in terms of CA and CA hysteresis. These surfaces show very high adhesion force to water droplets; in essence, the strong adhesion force is owing to the combination of capillary force derived from newly generated micro-porosity of substrate and the interaction between amidic groups of coating and water molecules. Besides, they exhibit high stability and durability after water immersion test. This approach may provoke new ideas for creating superamphiphobic surfaces with special adhesion properties on porous substrates. Moreover, these materials could also be potentially employed as water repellents for porous building materials, since they are easy to handle and soluble in environmentally benign solvents. In addition to very high water inhibition efficiency, they manifest high residual vapor permeability and preserve the physical characteristics, i.e. vapor diffusivity and chromatic features, of substrate.

Wettability of AlSi7Mg alloy on alumina, spinel, mullite and rutile and its influence on the aluminum melt filtration efficiency

Despite the application of aluminum melt filtration with ceramic foam filters since the 1960s the process is not fully understood. Outstanding issues are for example the influence of the wetting behavior and filter chemistry on the filtration efficiencies.Contact angle measurements by the sessile drop method coupled with non-contact heating and capillary purification technique were conducted at 730 °C with AlSi7Mg alloy on the substrates of four different oxides (Al2O3, MgAl2O4, 3Al2O3·2SiO2 and TiO2). The highest contact angle was measured on 3Al2O3·2SiO2, followed by MgAl2O4, Al2O3 and TiO2.Experimental values of contact angles were correlated with the evaluated filtration efficiencies of filtration trials performed at Constellium. They show a good correlation for inclusions smaller than 110 μm - the larger the contact angle the higher is the filtration efficiency.The adhesion forces of alumina inclusions on the four filter materials were experimentally estimated with an AFM in water based model system. The highest adhesion forces were measured on the Al2O3 substrate, followed by the 3Al2O3·2SiO2, the MgAl2O4 and the TiO2 substrate. For inclusions >70 μm, both the measured filtration efficiencies for >70 μm and the adhesion forces increase by the following order of coatings: TiO2, 3Al2O3·2SiO2, MgAl2O4, Al2O3.

Effects of physically deposited multilayer graphene platelet and graphite on tribological performance of alumina on alumina contact

Multilayer graphene platelet and expanded graphite were deposited on alumina disk surface and their effects on tribological performance of an alumina–alumina contact in different environments were evaluated using a pin-on-disk tribometer. Experimental results indicate that coefficients of friction at the contact are reduced by deposited particles due to their lubricating effect. It is interesting to find that wear of the contact in dry conditions is less than that under liquid lubrication. Tribofilm plays a key role in the wear reduction performance. In liquid media, however, formation of tribofilm is limited due to fluid flow and formed thin tribofilm is not able to protect the contact from wear. Experimental results show that formation of tribofilm is improved by both multilayer graphene platelet and expanded graphite. This is attributed to the higher adhesion force between graphene and alumina than that between alumina and alumina. The findings demonstrate that deposition of graphene-based materials onto alumina surface hold the promise of providing a new pathway to increase the anti-wear performance of alumina and possibly other ceramics.

Prediction of the minimum fluidization velocity of particles of sugarcane bagasse

This study refers to an experimental analysis of the fluid-dynamics of particles of sugarcane bagasse in a fluidization column with an internal diameter of 190 mm, which determined the minimum fluidization velocity of the particles with different characteristic diameters (0 < dp<9.5 mm), using air as fluidization means. The results have shown that the minimum fluidization velocity has a tendency to increase as the diameter of the particle increases. However, in a certain range of diameter (0.88 mm < dp<9.5 mm), where the particles have a high aspect ratio (length/diameter), it has not been possible to fluidize them. High superficial air velocities have been used, mainly due to the strong trend to interlace and to develop high adhesion forces in this type of particles, as well as the high porosity that is displayed. Based on the experimental results, two new models have been developed in order to determine the minimum fluidization velocity and the complete fluidization velocity of the sugarcane bagasse with diameters that range from 0.075 to 0.445 mm. The comparisons have been made by using correlations from the literature for the determination of the minimum fluidization velocity, and the experimental results have shown that the new suggested correlations finely predict this parameter, with a maximum error range of 6%, respecting the experimental values.

Bioinspired Pressure-Tolerant Asymmetric Slippery Surface for Continuous Self-Transport of Gas Bubbles in Aqueous Environment.

Biosurfaces with geometry-gradient structures or special wettabilities demonstrate intriguing performance in manipulating the behaviors of versatile fluids. By mimicking natural species, that is, the cactus spine with a shape-gradient morphology and the Picher plant with a lubricated inner surface, we have successfully prepared an asymmetric slippery surface by following the processes of CO2-laser cutting, superhydrophobic modification, and the fluorinert infusion. The asymmetric morphology will cause the deformation of gas bubbles and subsequently engender an asymmetric driven force on them. Due to the infusion of fluorinert, which has a low surface energy (∼16 mN/m, 25 °C) and an easy fluidic property (∼0.75 cP, 25 °C), the slippery surface demonstrates high adhesive force (∼300 μN) but low friction force on the gas bubbles. Under the cooperation of the asymmetric morphology and fluorinert infused surface, the fabricated asymmetric slippery surface is applicable to the directional and continuous bubble delivery in an aqueous environment. More importantly, due to the hard-compressed property of fluorinert, the asymmetric slippery surface is facilitated with distinguished bubble transport capability even in a pressurized environment (∼0.65 MPa), showing its feasibility in practical industrial production. In addition, asymmetric slippery surfaces with a snowflake-like structure and a star-shaped structure were successfully fabricated for the real-world applications, both of which illustrated reliable performances in the continuous generation, directional transportation, and efficient collection of CO2 and H2 microbubbles.

Superwettable Electrochemical Biosensor toward Detection of Cancer Biomarkers.

Bioinspired superwettable micropatterns that combine two extreme states of superhydrophobicity and superhydrophilicity with the ability to enrich and absorb microdroplets are suitable for versatile and robust sensing applications. Here we introduce a superwettable microchip that integrates superhydrophobic-superhydrophilic micropatterns and a nanodendritic electrochemical biosensor toward the detection of prostate cancer biomarkers. On the superwettable microchip, the superhydrophobic area could confine the microdroplets in superhydrophilic microwells; such behavior is extremely helpful for reducing the amount of analytical solution. In contrast, superhydrophilic microwells exhibit a high adhesive force toward microdroplets, and the nanodendritic structures can improve probe-binding capacity and response signals, thus greatly enhancing the sensitivity. Sensitive and selective detection of prostate cancer biomarkers including miRNA-375, miRNA-141, and prostate-specific antigen on a single microchip is also achieved. Such a superwettable microchip with high sensitivity, low sample volume, and upside-down detection capability in a single microdroplet shows great potential to fabricate portable devices toward complex biosensing applications.

Adhesion forces of the sea-water bacterium Paracoccus seriniphilus on titanium: Influence of microstructures and environmental conditions.

The bacterial attachment to surfaces is the first step of biofilm formation. This attachment is governed by adhesion forces which act between the bacterium and the substrate. Such forces can be measured by single cell force spectroscopy, where a single bacterium is attached to a cantilever of a scanning force microscope, and force-distance curves are measured. For the productive sea-water bacterium Paracoccus seriniphilus, pH dependent measurements reveal the highest adhesion forces at pH 4. Adhesion forces measured at salinities between 0% and 4.5% NaCl are in general higher for higher salinity. However, there is an exception for 0.9% where a higher adhesion force was measured than expected. These results are in line with zeta potential measurements of the bacterium, which also show an exceptionally low zeta potential at 0.9% NaCl. In the absence of macromolecular interactions, the adhesion forces are thus governed by (unspecific) electrostatic interactions, which can be adjusted by pH and ionic strength. It is further shown that microstructures on the titanium surface increase the adhesion force. Growth medium reduces the interaction forces dramatically, most probably through macromolecular bridging.

Zein film functionalized atomic force microscopy and Raman spectroscopic evaluations on surface differences between hard and soft wheat flour

Fundamental differences exist between the surfaces of hard and soft wheat flours. Ranging from surface roughness, chemical composition to cohesive forces, these differences could affect the flow behaviour of wheat flour. In an attempt to address these differences, we developed a zein film functionalized atomic force microscopy technique to evaluate the surface forces on compacts of hard, soft wheat flour, and its pure components, starch and gluten. Using the pure wheat components as the baseline, we analyzed the chemical compositional differences via Raman spectroscopy coupled with Band–Target Entropy Minimization (BTEM®) algorithm. The zein film functionalization distinguishes between wheat starch and gluten with stronger interactions on starch at least twice that of gluten. In general, soft wheat flour has higher adhesion forces than hard wheat flour of the same particle size. Higher starch content at the expense of protein in soft wheat flour seems to suggest the difference. However, the microstructural difference of starch granules on the compacted surface could describe more adequately the effect of particle size on the interaction forces.

Multibond Model of Single-Asperity Tribochemical Wear at the Nanoscale.

Single-asperity wear experiments and simulations have identified different regimes of wear including Eyring- and Archard-like behaviors. A multibond dynamics model has been developed based on the friction model of Filippov et al. [Phys. Rev. Lett. 92, 135503 (2004)]. This new model captures both qualitatively distinct regimes of single-asperity wear under a unified theoretical framework. In this model, the interfacial bond formation, wearless rupture, and transfer of atoms are governed by three competing thermally activated processes. The Eyring regime holds under the conditions of low load and low adhesive forces; few bonds form between the asperity and the surface, and wear is a rare and rate-dependent event. As the normal stress increases, the Eyring behavior of wear rate breaks down. A nearly rate-independent regime arises under high load or high adhesive forces, in which wear becomes very nearly, but not precisely, proportional to sliding distance. In this restricted regime, the dependence of wear rate per unit contact area is nearly independent of the normal stress at the point of contact. In true contact between rough elastic surfaces, where contact area is expected to grow linearly with normal load, this would lead to behavior very similar to that described by the Archard equation. Detailed comparisons to experimental and molecular dynamics simulation investigations illustrate both Eyring and Archard regimes, and an intermediate crossover regime between the two.