Decrease In Adhesion Force Research Articles

Investigating the influence of chromium layer thickness on thermal stability, adhesion and agglomeration of Cr/Ag/Cr sandwich layers in microelectromechanical systems (MEMS)

This study explores the influence of chromium layer thickness on the thermal stability and agglomeration of Cr/Ag/Cr sandwich layers used in MEMS applications. Achieving uniform and consistent deposition of thin films is crucial for optimal device performance. Magnetron sputtering, a technique offering precise control over film properties, is commonly employed for depositing thin films in MEMS. Silver is a popular choice due to its desirable properties, but it tends to agglomerate at high temperatures. The researchers investigated the effect of chromium layer thickness on thermal stability and agglomeration. They deposited chromium layers of varying thicknesses onto silicon substrates, followed by a silver layer and another chromium layer to create a sandwich structure. Annealing was performed at different temperatures to assess thermal stability and prevent silver agglomeration. Thermal stability was evaluated by measuring electrical resistance using a four-point probe method, and surface topography was analyzed using a non-contact atomic force microscope. The goal was to identify the optimal chromium layer thickness to minimize agglomeration and maximize thermal stability. The results showed that a sandwich structure with a 5 nm top chromium layer (Si/Cr (5 nm)/Ag (100 nm)/Cr (5-10-15-20 nm)) exhibited decreased adhesion force with increasing annealing temperatures. The use of a chromium sandwich layer significantly reduced surface roughness, as indicated by reductions in Ra and RMS values. A 15 nm thick chromium layer above and below the silver layer provided the best thermal stability and prevented silver agglomeration, resulting in the highest degree of adhesion. This thickness also yielded optimal surface parameters for the chromium sandwich layers at the annealing temperatures. In conclusion, the study demonstrates that the thickness of the chromium layer influences thermal stability, agglomeration, and surface parameters in MEMS applications and enables better control over thin film deposition.

Probing the reduction of adhesion forces between biofilms and anti-biofouling filtration membrane surfaces using FluidFM technology

Biofouling is a persistent problem in many sectors (healthcare, medicine, marine, and membrane filtration processes). To control the biofouling of surfaces, it is essential to overcome or reduce the adhesion forces between biofilms and surfaces. To access and understand the molecular basis of these interactions, atomic force microscopy (AFM) is a well-suited technology that can measure adhesion forces at the piconewton level. However, AFM-based existing methods only probe interactions between individual cells and surfaces, which is not representative of realistic conditions given that bacteria mainly exist in biofilms. We develop here an original method using FluidFM, a combination of AFM and microfluidics, to probe the adhesion forces between biofilms and filtration membranes modified with an anti-biofouling agent, vanillin. This strategy involves i) growing bacterial biofilms on micrometer-sized polystyrene beads, ii) aspirating these biofilm beads at the aperture of microfluidic cantilevers and iii) using them as probes in force spectroscopy experiments. The results obtained first showed that COOH-functionalized polystyrene beads are more suitable for bacterial growth, and that biofilms obtained after 3 h of incubation could be used with FluidFM. Then, biofilm-scale force spectroscopy experiments showed a significant decrease in adhesion forces, adhesion work, and adhesion events after membrane modification, demonstrating the potential of vanillin-coated membranes to reduce biofouling. In addition, the comparison between results at the individual cell and biofilm scales highlighted the complexity of polymeric matrix unbinding and/or unfolding in the biofilm, showing that individual cells behave differently from biofilms. Overall, this method could have implications in the fields of materials science, chemical engineering, health, and the environment.

Skin‐customized wearable device adhesive without skin damage

AbstractWearable medical devices are gaining popularity owing to their potential for seamless integration with the human body and long‐term monitoring of physiological activity. However, conventional adhesives were developed based on the assumption of healthy adult skin and may not account for variations in skin characteristics across different species, environments, and body parts. Consequently, the adhesive strength of wearable devices may significantly differ depending on the skin surface to which they are attached, potentially causing skin damage. In this study, we developed a customized wearable‐device adhesive without skin damage by analyzing the characteristics of the skin surface based on oil and water content and roughness according to different species and parts. Our findings demonstrated that increased root‐mean‐square roughness of the skin surface led to reduced contact area and decreased adhesion force between the polydimethylsiloxane (PDMS) pad and skin surface. Surprisingly, hairless skin exhibited 1.5 times higher adhesion strength than hairy skin due to stronger molecular forces resulting from the higher surface energy of the skin. Additionally, the hole‐patterned PDMS pad on sweaty skin displayed improved adhesion properties compared to the cylinder‐patterned PDMS pad. Therefore, customized wearable adhesives provide an effective strategy for developing skin‐damage‐free wearable devices.

Nonmonotonic dependence of adhesion between liquid aluminum and silicon surface on the temperature of the surface

In this paper, the effect of temperature on the adhesion properties between liquid aluminum (Al) and solid silicon (Si) in the presence and absence of vacancy defects is elucidated. Firstly, the perfect defect-free and vacancy defect models consist of crystalline Al probe and Si substrate are established by classical molecular dynamics simulation method. Then, the melting and adhesion process of probe Al are simulated, and the adhesion performance and microscopic permeation evolution of liquid Al/solid Si are analyzed. The results show that the adhesion force changes nonmonotonically with increasing substrate temperature T without vacancy defects. Specifically, when the substrate temperature varies at relatively low values smaller than the melting point of Al, that is, 100 K < T < 933 K, the thermal excitation provides more energy to the substrate Si atoms, which intensifies the aggregation of the substrate atoms, makes the interfacial atoms more dense and the number of atoms permeating into the substrate decreases, resulting in a decrease in adhesion force. On the contrary, when 933 K < T < 1500 K, due to the thermal effect, higher temperatures intensify the thermal vibration of the substrate atoms, resulting in violent collisions between the interfacial atoms, and the space for free movement increases, thus making the distance between the atoms larger. And the number of Al atoms permeating into the substrate Si increases, leading to an increase in interfacial adhesion. Furthermore, the adhesion force shows an upward trend with the elevated temperature in the presence of vacancy defects at low temperatures, this is attributed to the fact that more atoms are broken away from the equilibrium lattice structure, and the number of permeating atoms increases by increasing temperature. In particular, the interfacial adhesion is the largest when the vacancy defects of the substrate are the most serious.

Time-dependent plastic behavior of bacteria leading to rupture

A study of the mechanical response of bacteria is essential in designing an antibacterial surface for implants and food packaging applications. This research evaluated the mechanical response of Escherichia coli under different loading conditions. Indentation and prolonged creep tests were performed to understand their viscoelastic-plastic response. The results indicate that varying loading rates from 1 μm/s to 5 μm/s show an increase in modulus of 182% and 90%, calculated in the loading and unloading cycles, respectively, and a decrease in adhesion force by 42%. However, on varying loads from 5 nN to 25 nN, nominal change is observed in both modulus and adhesion force. The rupture curve at 100 nN load shows elastic and a small plastic deformation accompanied by a sharp peak indicating the cell wall rupture. The rupture force at the peak was found to be 34.38 ± 5.15 nN, irrespective of the loading rate, making it a failure criterion for bacteria rupture. The creep response of bacteria increases (for 6 s) and then remains constant (for 15 s) with time, indicating that a standard linear solid (SLS) model applies to this behavior. This work attempts to evaluate the mechanical properties of E. coli bacteria focusing on its rupture by contact killing mechanism.

Investigation on microscopic forces between methane hydrate particles in gas phase dominated system

Hydrate aggregation and deposition on the pipe wall are the main causes of hydrate plugging in pipelines. Microscopic forces between hydrate particles are an important reference for determining the behavior of aggregation or separation from the pipe wall of hydrate particles. Based on a high-pressure visual micro-force measurement system, this study measured the hydrate particle-hydrate particle cohesive force and hydrate particle–wall liquid droplet adhesion force under pure water, as well as hydrate particle–wall liquid droplet adhesion force under anti-agglomerants (AAs). It was found that the magnitude of hydrate particle-hydrate particle cohesive force was ×10 mN/m, and the magnitude of hydrate particle–wall liquid droplet adhesion force was ×103 mN/m. The effects of 4 AAs in the methane gas-dominated system were evaluated from a micro-perspective, revealing that after adding DDBAB, D1021, AEO-9, and CDEA, the maximum reduction of adhesion force was 67%, 64%, 51%, and 53% compared with that under pure water, respectively. The mechanism of AAs reducing adhesion force was further explored, revealing that the adhesion force arose from a liquid bridge and was affected by the gas–water interfacial tension of solutions at low subcoolings. While at high subcoolings, the force was determined by the combined force of the liquid bridge and the hydrate shell. The addition of AAs reduced the gas–water interfacial tension of solutions, and the steric hindrance effect of AA molecules also weakened the tensile strength of the hydrate shell, leading to a decreased adhesion force. These experimental data can help deepen our understanding of the microscopic forces between methane hydrate particles, and provide experimental data and scheme design basis for wellbore flow assurance of deepwater gas wells.

Interfacial Adhesion Forces of Hydrate Particles in the Presence of Hydrate Inhibitors

Hydrate inhibitors are traditionally utilized to prevent hydrate plugging. In this study, the adhesion forces of cyclopentane (CP) hydrates with thermodynamic inhibitors (ethanol, urea, and NaCl) and anti-agglomerant inhibitors [sorbitan monooleate (Span 80) and lecithin] were measured to understand the effects of hydrate inhibitors on the adhesion forces of hydrates. It was found that the thermodynamic inhibitors increased the early hydrate interparticle adhesion force due to the enhanced liquid bridge force. However, the liquid bridge acted as a lubricant layer to prevent the irreversible agglomeration of hydrate after long-term contact. The hydrate adhesion forces decreased by 90.5-93.0% and 76.6-92.7% with an increase in the concentration of Span 80 and lecithin, respectively, from 0.1 to 1 wt %. Both rough morphology and low interfacial tension contributed to the adhesion force decrease of hydrate after the addition of anti-agglomerant inhibitors. The results may be helpful for understanding the mechanism of influence and quantifying the impact of hydrate inhibitors on hydrate interparticle adhesion force.

AFM characterization of physical properties in coal adsorbed with different cations induced by electric pulse fracturing

Pore system in coal is highly heterogeneous, while it is the main occurrence space and transport channel for coalbed methane (CBM). Electric pulse fracturing (EPF) has been considered as an effective approach to improve the coal physical properties for better CBM production. In this work, based on AFM measurement of 40 coal samples collected from Qinshui Basin, we evaluated the physical properties of coal, adsorbed with different cations, after EPF. This was accomplished by first analyzing the breakdown field response process of coal adsorbed with different cations, and then determining the dynamic changes of pore and surface roughness using the watershed method. In the PeakForce QNMTM model, the heterogeneous distribution of the adhesion force with increasing cation valence was quantified. The results show that the ability of medium- and high-rank coals to adsorb cations exhibits in the order of Fe3+ > Ca2+ > K+, attributed to the decrease in the radius of hydrated ions with increasing ionic valence. When the electric field is applied to both ends of coal sample, the plasma channels in coal generate huge energy, resulting in the temperature rise of pore-fracture and throat. Affected by EPF, the porosity of Chengzhuang (CZ) increases from 4.1% to 27.4%, greater than that of Qiyi (QY) from 6.7% to 14.5%. In the surface morphology tests, the surface skewness Rsk of QY adsorbed with different valence cations shifts from positive to negative values, reflecting the change of coal surface height from the right-skewed normal distribution to the left-skewed one. Moreover, the area where the surface height of QY adsorbed cation is below the average value gradually increases with the increase of the chemical valence. For micromechanical properties, the adhesion force of CZ adsorbed with different cations ranges from 0.9 to 20.7 nN, which is less than QY overall. This is mainly due to the weakening of intermolecular forces on the coal surface with the deepening of coalification, resulting in a decrease in adhesion force. Therefore, this study provides new insights into the differences in gas production mechanisms of CBM wells in the same coal seam from different regions.

Decrease in adhesion force at silica-mica interface with short contact time due to dynamic formation process of liquid bridge revealed on an AFM

ABSTRACT The influence of instrumental parameters of an atomic force microscope (AFM) on adhesion forces demands clarification. Adhesion forces between a tipless cantilever and mica were measured in a humid environment to investigate the influence of instrumental parameters. The adhesion force measured repeatedly at a location is relatively stable with excellent reproducibility. The force abnormally decreases by ~10% with dwell time (0 ~ 0.4 s), then remains almost stable (0.4 ~ 10 s). The reason was the dynamic formation process of a liquid bridge. Due to a large driving pressure, the volume of the liquid bridge can increase intensely to the maximum one, which is larger than that in saturation. This leads to the reduction in the bridge by liquid flow, eventually resulting in the decrease. The force increases by a small magnitude with approach velocity and then remains stable. However, it increases logarithmically with retraction velocity and increases with piezo velocity with a concave downward shape in the logarithmic coordinate. The velocity dependence was ascribed to the dynamic enhancement of viscous force and the contact time dependence. The outcomes may help to understand the influence of instrumental parameters, and deepen the understanding of the formation mechanism of a liquid bridge.

Evaluation of azoximer bromide (polyoxidonium) influence on the adhesive properties of the Yersinia pestis EV NIIEG vaccine strain by atomic force microscopy

Aim. To characterize the influence of azoximer bromide (polyoxidonium, PO) in cultivation conditions on the morpho- and nanomechanical cell surface properties of Y. pestis EV NIIEG vaccine strain and its derivatives Y. pestis КМ218 (pYT–, pYV–, pYP–), Y. pestis КМ216 (pYT–, pYV–, pYP+), Y. pseudotuberculosis, Y. enterocolitica by atomic force microsopy (AFM), as well as on the adhesion of cells Y. pestis EV NIIEG to human collagen type IV.Materials and methods. The measurements were carried out using the Solver P47-PRO probe microscope (NT-MDT, Russia), standard methods of semi-contact AFM and AFM imaging analysis program. The adhesion of Y. pestis EV NIIEG to type IV collagen was determined by the number of cells binding to glass slides covered with human collagen type IV.Results. The introduction of PO in the cultivation environment caused changes in the morphometric parameters of the cells of Y. pestis EV NIIEG vaccine strain and its isogenic derivatives (increase in volume, flatten ingested (S/H), index I (W/H). These changes were accompanied by the transformation of nanomechanical properties of the cell surface (reducing the root mean square, adhesion force), which countenance was associated with the plasmid profile. The lesser decrease of adhesion force in the absence of changes of the index I was observed in cells Y. pseudotuberculosis and Y. enterocolitica with plasmid pYV. In the strain Y. enterocolitica KM383 (pYV–) PO did not induce significant changes in the indicators studied. The introduction of the PO into the cultivation environment decreased the ability of Y. pestis EV cells to bind to human collagen type IV. Modification by PO the adhesive properties of the vaccine strain Y. pestis EV NIIEG was accompanied by an increase in its immunogenicity.

Surface Forces between Nanomagnetite and Silica in Aqueous Ca2+ Solutions Studied with AFM Colloidal Probe Method

Dispersion and aggregation of nanomagnetite (Fe3O4) and silica (SiO2) particles are of high importance in various applications, such as biomedicine, nanoelectronics, drug delivery, flotation, and pelletization of iron ore. In directly probing nanomagnetite–silica interaction, atomic force microscopy (AFM) using the colloidal probe technique has proven to be a suitable tool. In this work, the interaction between nanomagnetite and silica particles was measured with AFM in aqueous Ca2+ solution at different pH levels. This study showed that the qualitative changes of the interaction forces with pH and Ca2+ concentrations were consistent with the results from zeta-potential measurements. The repulsion between nanomagnetite and silica was observed at alkaline pH and 1 mM Ca2+ concentration, but no repulsive forces were observed at 3 mM Ca2+ concentration. The interaction forces on approach were due to van der Waals and electrical double-layer forces. The good fitting of experimental data to the DLVO model and simulations supported this conclusion. However, contributions from non-DLVO forces should also be considered. It was shown that an increase of Ca2+ concentration from 1 to 3.3 mM led to a less pronounced decrease of adhesion force with increasing pH. A comparison of measured and calculated adhesion forces with a few contact mechanics models demonstrated an important impact of nanomagnetite layer nanoroughness.

Direct Evidence of Salinity and pH Effects on the Interfacial Interactions of Asphaltene-Brine-Silica Systems.

The hydraulic fracturing technique remains essential to unlock fossil fuel from shale oil reservoirs. However, water imbibed by shale during hydraulic fracturing triggers environmental and technical challenges due to the low flowback water recovery. While it appears that the imbibition of fracturing fluid is a complex function of physico-chemical processes in particular capillary force which is associated with wettability of oil-brine-shale, the controlling factor(s) to govern the wettability is incomplete and the literature data in this context is missing. We thus measured the adsorption/desorption of asphaltenes on silica surface in the presence of brines using quartz crystal microbalance with dissipation (QCM-D). We detected zeta potential of asphaltene-brine and brine-silica systems and calculated the disjoining pressures of the asphaltene-brine-silica system in the case of different salinity. Moreover, we performed a geochemical study to quantify the variation of surface chemical species at asphaltene and silica surfaces with different pH values and used the chemical force microscope (CFM) method to quantify the effect of pH on intermolecular forces. Our results show that lowering salinity or raising pH reduced the adhesion force between asphaltene and silica surface. For example, at a pH value of 6.5, when the concentration of injected water is reduced from 1000 mM to 100 mM and 10 mM, the adhesion force decreased by approximately 58% and 66%, respectively. In addition, for the 100 mM NaCl solution, when the pH value increased from 4.5 to 6.5 and 9, the adhesion force decreased by approximately 56% and 87%, respectively. Decreased adhesion forces between asphaltene and the silica surface could promote the desorption of asphaltene from the silica surface, resulting in a negative zeta potential for both asphaltene-silica and brine-silica interfaces and a shift of wettability towards water-wet characteristic. During such a process, -NH+ number at asphaltene surfaces decreases and the bonds between -NH+ and >SiO− break down, to further interpret the formation of a thinner asphaltene adlayer on the rock surface. This study proposes a reliable theoretical basis for the application of hydraulic fracturing technology, and a facile and possible manipulation strategy to increase flowback water from unconventional reservoirs.

THE MEASUREMENT OF ADHESION FORCES IN THE SYSTEM «CELL-CELL» BY USING ATOMIC FORCE MICROSCOPE

The objective was to develop a biosensor chip based on lymphocytes for studying the adhesion properties of the cells; to measure the adhesion forces between blood cells in normal and pathological conditions. In research standard cantilever CSG 11/tipless series (USA) was treated with 2% gelatin solution. After that, the lymphocyte was attached to it from the prepared leukocyte suspension placed on the glass. The preparation of the sensor was done in the power spectroscopy mode during the scan by single pressing on the cell. The patients’ peripheral blood with acute lymphoblastic and acute myeloblastic leukemia was used for measuring adhesion forces among cells at the treatment and recurrence stage. The obtained data shows that the objective criteria of the beginning state of the recurrence of the lymphoproliferative processes is an increase in the forces of the intercellular interactions in the lymphocyte-granulocyte system, while the recurrence of myeloid lineage proliferation of haemopoiesis causes a decrease in adhesion forces in the same system. This result gives the possibility to predict and identify early micro-rheological changes at the beginning of decompensation of the remission state at the cellular level during the development of malignant proliferative processes in the blood system.

PENGARUH PENGGUNAAN TEPUNG TAPIOKA DALAM PEMBUATAN LEM TEGEL KARET

The purpose of this research is to know effect the addition of tapioca flour to adhesiveness and viscosity of the tile compound rubber glue formulations using filler material. The tile compound rubber glue made from mixture of tapioca flour as filler material. Design research with variation of tapioca flour such as formula A (8 g of tapioca flour), formula B (12 g of tapioca flour), formula C (16 g of tapioca flour), formula D (20 g of tapioca flour) and formula E (24 g tapioca flour) and F (requirements generally and comparison glue). The result showed that the addition of tapioca flour have significant effects on the adhesiveness and viscosity of glue. The higher the addition of tapioca flour (24 g), the adhesiveness would be lower (1.78 kg / in) because of decreased adhesion force. Tiles rubber compound glue formula complied with requirements generally glue (the adhesiveness value of 4.395 kg / in and the Brookfield viscosity value of 98.275 cP is the B formula (tapioca flour 12 g) with an adhesiveness value of 4.17 kg / in and viscosity value 51.33 cP.

Conversion of wood-biopolymers into macrofibers with tunable surface energy via dry-jet wet-spinning

Surface chemistry of regenerated all-wood-biopolymer fibers that are fine-tuned by composition of cellulose, lignin and xylan is elucidated via revealing their surface energy and adhesion. Xylan additive resulted in thin fibers and decreased surface energy of the fiber outer surfaces compared to the cellulose fibers, or when lignin was used as an additive. Lignin increased the water contact angle on the fiber surface and decreased adhesion force between the fiber cross section and a hydrophilic probe, confirming that lignin reduced fiber surface affinity to water. Lignin and xylan enabled fiber decoration with charged groups that could tune the adhesion force between the fiber and an AFM probe. The fibers swelled in water: the neat cellulose fiber cross section area increased 9.2%, the fibers with lignin as the main additive 9.1%, with xylan 6.8%, and the 3-component fibers 5.5%. This indicates that dimensional stability in elevated humidity is improved in the case of 3-component fiber compared to 2-component fibers. Xylan or lignin as an additive neither improved strength nor elongation at break. However, improved deformability was achieved when all the three components were incorporated into the fibers.Graphical

Nanopurpurin-based photodynamic therapy destructs extracellular matrix against intractable tumor metastasis

Nanomaterials-based photodynamic therapy (PDT) has been used to treat malignant cells. However, the intrinsic impact of nanomaterials-based PDT on mechanical properties of intractable tumor cells is not well understood. Herein, we demonstrated that the mechanical forces of Taxol-resistant tumor cells were decreased by nanopurpurin-based PDT destructing extracellular matrix (ECM), increasing therapy sensitivity and repressing tumor metastasis. Combining FIRMS and general confocal microscope, we observed that the disruption of ECM by photodynamic reaction of P18-nanoconfined liposome (P18⊂L) induced a decrease of adhesion force and biomechanical properties of Taxol-resistant cells through the attenuation of actomyosin-based contractility thereby inhibiting cell migration and metastasis in vivo. Moreover, the destroyed ECM by P18⊂L PDT increased the therapy sensitivity. A clearer understanding of the effect of nanopurpurin-based PDT on mechanical properties and behaviors of intractable tumor cells will provide new and important basis for developing new therapeutic strategies.

The anti-soiling performance of highly reflective superhydrophobic nanoparticle-textured mirrors.

The anti-soiling (AS) performance of solar mirrors coated with a highly transparent, superhydrophobic nanoparticle-textured coating has been characterized. The AS coatings were created on the mirror surface by depositing nano-textured silica nanoparticle layers of ∼250 nm thickness using a draw-down coating process, followed by fluorination of the nanoparticles in a molecular vapor deposition process. Highly uniform surface features of the AS-coated mirrors (20 × 30 cm2, no measurable loss in specular reflectance, and water contact angle >165°) provided an outstanding AS performance. A 4× reduction in the rate of dust accumulation as determined by gravimetric measurement of the accumulated dust on coated versus uncoated mirrors was observed. Additional evidence of a significant reduction in soiling rate was determined during measurements of specular reflectance in an outdoor environment test. The adhesion force between a model sand particle and nano-textured coatings in the hydrophobic to superhydrophobic range was also studied. A dramatic decrease in adhesive force acting on the particle was observed with increasing surface hydrophobicity. The results align well with the observed dust accumulation on the AS-coated mirrors. The AS-coated mirror maintains a high reflectivity by shedding dust and resisting dust accumulation, providing a potential benefit when applied to mirrors in the solar field of a concentrated solar power generation plant.

Investigation of reclaimed asphalt pavement blending efficiency based on micro-mechanical properties of layered asphalt binders

The challenge in mix design and application of reclaimed hot mix asphalt (HMA) lies in the unknown blending efficiency between reclaimed asphalt pavement (RAP) binder and virgin binder. By using a combination of staged extraction method and Atomic Force Microscopy (AFM) imaging technique, this paper focused on the investigation of interaction and extent of blending between RAP-virgin binders under different mixing temperature and residence time, based on the micro-mechanical properties of layered binders in real reclaimed HMA. In addition, the impact of chemical solvent used in staged extraction, i.e. Trichloroethylene (TCE), on the AFM images of extracted asphalt binder was also explored. It was found that the topographic features of asphalt binder in terms of “bees” structure were obviously altered by TCE, which were not suitable for analysis on RAP blending. A possible blending scenario, indicating non-homogenous blending between RAP-virgin binders in the layered binder system, was put forward for the mixing stage of reclaimed HMA, in which increased DMT modulus and decreased adhesion force and energy dissipation were observed from the outermost towards to the innermost layers. Both mixing temperature and residence time have significant effects on the blending efficiency between RAP-virgin binders. With the decrease of mixing temperature, diffusion of the virgin binder into RAP binder is impaired, thus leading to less blending efficiency between the two binders. Besides the mixing process, the blending between RAP-virgin binders continues with the passing residence time, until a complete and homogeneous blending being reached after sufficiently long time.

Anti-adhesive Property of Maize Leaf Surface Related with Temperature and Humidity

The anti-adhesive surfaces have always aroused great interest of worldwide scientists and engineers. But in practical applications, it often faces the threat and impact of temperature and humidity. In this work, the excellent anti-adhesive performance of maize leaf under high temperature and humidity were investigated in detail. Firstly, the adhesion forces of the maize leaf surface under different temperature and humidity were measured by using Atomic Force Microscopy (AFM). The temperature of the substrate was varied between 23 °C to 100 °C, and the ambient relative humidity is from 18% to 100%. It was found that the adhesion force of maize leaf decreased with the increase of temperature and humidity. The mechanism of its excellent anti-adhesive performance of maize leaf under high temperature and relative humidity was revealed. The transverse and longitudinal ridges on maize leaf surface interlace with each other, forming small air pockets, which reduces the actual contact area between the object and the maize leaf. With the increase of humidity, the liquid film will be formed in the air pockets gradually and so much water vapor is produced with increase of temperature. Then the air flow rate increases though the wavy top of transverse ridges, inducing the dramatic decrease of adhesion force. Inspired by this mechanism, four samples with this bionic structure were made. This functional “biomimetic structure” would have potential value in the wide medical equipments such as high frequency electric knife with anti-adhesion surface under high temperature and high humidity.

Logarithmic decrease of adhesion force with lateral dynamic revealed by an AFM cantilever at different humidities

ABSTRACTAdhesion forces between a tipless cantilever and an Au film were determined to investigate the influence of lateral velocity by recording force curves with an atomic force microscope at 20%–90% relative humidities. The sample was moved laterally, forth and back, with a frequency of 0.001–100 Hz and scan distances of 0.8, 8, and 80 μm to achieve a velocity ranging over 7 orders of magnitude. Experimental results show that at low lateral velocities (between 1.6 nm/s and 1–10 μm/s), the adhesion force either increases or decreases or remains stable with the lateral velocity without a certain characteristic trend. However, after a critical velocity, the adhesion force decreases logarithmically with the lateral velocity (between 1–10 and 16,000 μm/s). The decreasing magnitude can be as large as 97.3% of the maximum adhesion force. This decrease is well-explained by the contact time dependence of water bridges formed by capillary condensation.