Increase In Adhesion Force Research Articles

Adhesion force between cyclopentane hydrates and solid surface materials

The mechanisms by which hydrates deposit in a petroleum production line are related to pipeline surface properties, fluid composition and properties, and water cut. In this work, adhesion forces between cyclopentane hydrates and solid surfaces were investigated as a function of the solid material, the presence of water and the presence of petroleum acids in the oil phase. The influence of dissolved water on hydrate adhesion forces was also investigated. The results show that the adhesion force between hydrates and solid surfaces was dependent on the surface material; solids with low surface free energy lead to the lowest adhesion forces. The adhesion force was strongly dependent on the presence of water in the system. When a water drop was deposited on the solid surface, the adhesion force between the hydrate and the solid surface was more than 10 times larger than hydrate–hydrate adhesion forces. The presence of a water-saturated oil phase also led to an increase in adhesion force between hydrate particles. Adhesion forces were highest when the solid surfaces are water-wet. Addition of petroleum acids to the oil phase drastically reduced adhesion forces.

Measurement method and results of ice adhesion force on the curved surface of a wind turbine blade

Experimental adhesion force measurements were conducted on accumulated ice on the leading edge of a scaled wind turbine blade in both glaze and rime icing regimes. An apparatus was first designed for specifically measuring the adhesion force of ice on a curved surface at climatic temperature where a vertical force was applied to the mounted structure in the test apparatus. Adhesion force measurements were measured and adhesion pressure calculated for plain and ice-mitigated test specimens. Results are presented for the increase in force of ice adhesion over a curved surface area in proportion to degree centigrade decrease in temperature.

Understanding weathering of oil sands ores by atomic force microscopy

AbstractEffect of weathering on colloidal interactions between bitumen and oil sands solids was studied by atomic force microscopy (AFM). The change in bitumen chemistry due to weathering was found to have a negligible effect on the interactions of bitumen with solid particles. However, the increase in solid surface hydrophobicity due to ore weathering reversed the long‐range interaction forces between bitumen and solids from repulsive to attractive with a corresponding increase in adhesion force. The measured force profiles between bitumen and various solids can be well fitted with the extended DLVO theory by considering an additional attractive force. The attractive long‐range force and increased adhesion force make the separation of bitumen from solids more difficult and the attachment of fine solids on liberated bitumen easier, thereby leading to poor bitumen liberation and lower aeration efficiency. Such changes account for the observed poor processability of the weathered ores. © 2009 American Institute of Chemical Engineers AIChE J, 2009

Nanocomposites of lung surfactant and biodegradable cationic nanoparticles improve transfection efficiency to lung cells

The objective of this study was to develop highly efficient ternary nanocomposites for aerosol gene therapy consisting of a biodegradable polymer core, poly[vinyl-3-(diethylamino)propylcarbamate- co-vinyl acetate- co-vinyl alcohol]-graft-poly( d, l-lactide- co-glycolide), pDNA and a third component to alter surface properties, physicochemical characteristics and biological activity. The effects of the surface altering components lung surfactant, carboxymethyl cellulose (CMC) or poloxamer on nanocomposites were characterized with regard to size, zeta potential, cytotoxicity, biological activity and surface properties. With increasing concentrations of lung surfactant, CMC or poloxamer, sizes of nanocomposites increased. AFM nanoindentation measurements showed a significant increase in adhesion forces of nanocomposites compared to pure nanoparticles. Zeta potential values, cytotoxicity and intracellular uptake demonstrated a strong dependency on the surface altering component. While an excess of CMC led to a decreased uptake into cells due to the negative zeta potential, nanocomposites with lung surfactant displayed enhanced intracellular uptake. Transfection efficiency of nanocomposites with lung surfactant was 12-fold higher compared to pure nanoparticles and 30-fold higher compared to polyethylenimine in lung cells and could also be maintained after nebulization. Ternary nanocomposites prepared with lung surfactant proved to be a potent pulmonary gene delivery vector due to its high stability during aerosolization with a vibrating mesh nebulizer and favourable biological activity.

Role of Extracellular Polymeric Substances (EPS) in Biofouling of Reverse Osmosis Membranes

This study elucidates the mechanisms by which extracellular polymeric substances (EPS) impact permeate water flux and salt rejection during biofouling of reverse osmosis (RO) membranes. RO fouling experiments were conducted with Pseudomonas aeruginosa PAO1, EPS extracted from PAO1 biofilms, and dead PAO1 cells fixed in formaldehyde. While a biofouling layer of dead bacterial cells decreases salt rejection and permeate flux by a biofilm-enhanced osmotic pressure mechanism, the EPS biofouling layer adversely impacts permeate flux by increasing the hydraulic resistance to permeate flow. During controlled fouling experiments with extracted EPS in a simulated wastewater solution, polysaccharides adsorbed on the RO membranes much more effectively than proteins (adsorption efficiencies of 61.2-88.7% and 11.6-12.4% for polysaccharides and proteins, respectively). Controlled fouling experiments with EPS in sodium chloride solutions supplemented with 0.5 mM calcium ions (total ionic strength of 15 mM) indicate that calcium increases the adsorption efficiency of polysaccharides and DNA by 2- and 3-fold, respectively. The increased adsorption of EPS onto the membrane resulted in a significant decrease in permeate water flux. Corroborating with these calcium effects, atomic force microscopy (AFM) measurements demonstrated that addition of calcium ions to the feed solution results in a marked increase in the adhesion forces between a carboxylated particle probe and the EPS layer. The increase in the interfacial adhesion forces is attributed to specific EPS-calcium interactions that play a major role in biofouling of RO membranes.

In situ electrochemical Scanning Kelvin Probe Blister-Test studies of the de-adhesion kinetics at polymer/zinc oxide/zinc interfaces

Fundamental investigations of the polymer/zinc oxide/zinc interface corrosion stability were performed in situ by means of the electrochemical Height Regulated Scanning Kelvin Probe Blister-Test (HR-SKP-BT) under controlled atmospheric conditions. A hole under an adhesive layer film served as electrolyte reservoir to initiate cathodic de-adhesion processes. Then a combinatorial approach was undertaken to simultaneously study the influence of electrolyte pressure at constant defect polarisation and of relative atmospheric humidity on the de-adhesion rate. The time resolved blister growth and the propagation of the three phase boundary polymer/oxide covered zinc/interfacial electrolyte layer could be detected. It could be proven that the oxygen reduction induced electrochemical damage of the interface precedes the subsequent mechanical de-adhesion process. By variation of the relative atmospheric humidity the water concentration within the bulk adhesive and its interphase adjacent to the metal substrate could be adjusted. These processes were further analysed by peel-tests and in situ Attenuated-Total-Reflection Infrared Spectroscopy (ATR-IR) studies of water diffusion. A decrease of the interphasial water concentration led to a deceleration of the de-adhesion kinetics for constant defect conditions and to smaller interfacial ion transport rates. This could be assigned to an inhibition of the electron transfer reactions at the front of de-adhesion and an increased adhesion force between polymer film and oxide covered metal preventing the formation of an extended interfacial electrolyte layer.

Poisson Analysis of Streptococcal Bond Strengthening on Stainless Steel with and without a Salivary Conditioning Film

Poisson analysis of retract force-distance curves in atomic force microscopy (AFM) has yielded a new dimension to the decoupling of individual bond forces into a hydrogen bonding and nonspecific force component. Accordingly, bacterial adhesion forces have been decoupled into a hydrogen bonding and nonspecific Lifshitz-Van der Waals contribution. Due to the forced nature of AFM contact, the nonspecific force contribution has hitherto turned out to be repulsive in the analysis of bacterial adhesion forces on nonconducting surfaces. In this study, we present the results of a Poisson analysis of adhesion forces for streptococci adhering to a conducting surface. Adhesion forces measured between stainless steel, both in the absence and presence of an adsorbed salivary conditioning film, increased with increasing contact time between the streptococcal AFM probe and the surface. Concurrent with the increase in adhesion force, there was an increase in the number of minor force peaks in the retract force-distance curves. Poisson analyses of the adhesion forces indicated repulsive nonspecific Lifshitz-Van der Waals forces for streptococci adhering to saliva-coated stainless steel, but interestingly and for the first time, attractive nonspecific forces were revealed on stainless steel in the absence of a salivary conditioning film. We tentatively attribute this to attraction between the negatively charged streptococci and their positive image charges in the conducting material, which cannot develop in a nonconducting material or in the presence of a nonconductive protein layer on the stainless steel surface.

Adhesion force measurement between the stamp and the resin in ultraviolet nanoimprintlithography—an investigative approach

In the ultraviolet nanoimprint lithography (UV-NIL) process, the surface interactionbetween the mold and the resist is essential along with molecularly clean separation ofthe mold from the surface of the cured resist for repeated use of the mold. Inour present study, various mold–resin combinations have been examined by atensile strength method to determine the adhesion force between a mold with arelief pattern and a photocurable resin. The adhesion force of polymer moldsof the fluorine-containing polymers perfluoropolyether dimethacrylate (PFPE)and polydimethylsiloxane (PDMS) were compared to those of hard molds suchas Si and quartz against several commercial UV-NIL resins. Eventually, PFPEwith higher molecular weight—AMONIL—was found to be an excellent UV-NILmold–resin combination with the lowest adhesion force per unit area (20 kPa). Inparticular, the 36-fold repeated imprinting with a high molecular weight PFPE moldshowed only a slight increase of adhesion force by 36 kPa with molecularly cleanrelease from the AMONIL resin, whereas a surface-modified PDMS mold revealedhighly increased adhesion from an initial 20 kPa to 120 kPa after repeated use.

Technique to Measure Adhesive Forces Between Electrospun Nanofibers

AbstractDue to the difficulty in handling nanofibers, little is reported and understood on the dry adhesion between electrospun nanofibers. In this study, we develop a technique to measure the dry adhesive forces between electrospun nanofibers. Of critical importance is the ability to mimic naturally occurring dry adhesion such as that between gecko's and spider's foot hairs and untreated surfaces. The adhesion test was performed on two poly(e-caprolactone) electrospun ultrafine fibers using a nanoforce tensile tester. It was found that the adhesive force per unit area increased with decreasing fiber diameter. The degree of crystallinity, order parameters of macromolecules in the amorphous region and crystallite orientation of the spun fibers were determined by the differential scanning calorimetry (DSC) and wide angle X-ray diffraction (WAXD). The high measured adhesion between single PCL fibers in comparison to other reported values was attributed to crystal orientation due to electrospinning and the increase of adhesive force per unit area with decreasing fiber diameter.

Effects of defrosting period on mold adhesion force of epoxy molding compound

AbstractIn integrated circuit (IC) packaging, when epoxy‐molding compound (EMC) is filled in the mold cavity and cured in the mold, adhesion occurs in the interface between EMC and the mold surface. Too large an adhesion force can cause many problems. For example, too large an adhesion force may damage an IC during ejection and cause the package to fail and thus lower the yield rate. To resolve mold adhesion problems, improving the mold design and applying suitable surface treatments, such as mold surface coating, are the common approaches. Applying suitable surface coating is a more popular and practical approach. Defrosting is a process to increase the frozen EMC temperature to room temperature, and to retain it at room temperature for some period before molding. It is a common practice to put EMC under required atmospheric environment during defrosting. It has been found by molding engineers that increased defrosting period will increase the frequency of mold cleaning. But there is no quantitative description on how much the adhesion force increases during the defrosting process.This paper describes the use of a semiautomatic EMC adhesion force test instrument to measure the normal adhesion force between the mold surface and EMC. By measuring the adhesion force, one can quantify how much adhesion force exists between EMC and the mold surface under different defrosting periods. The results show that it is best to use the EMC with 24–32 h of defrosting, to prevent excessive amount of mold adhesion force and it has been found that the adhesion force of the 24 h defrosting period will be 24% less than that of the 48 h defrosting period. Decreasing moisture absorption will decrease the increase in adhesion force for prolonged defrosting period cases. Copyright © 2008 Curtin University of Technology and John Wiley & Sons, Ltd.

Physico-chemical characterization of a polycarbonate (PC) surface modified by exposure to dc glow discharge in air

The present investigation describes the changes in the wetting characteristics of a polycarbonate (PC) surface modified by exposure to dc glow discharge at 2.04 W, as observed by contact angle measurement. The contact angle of droplets of test liquids of deionized water and formamide on PC surface decreases rapidly with increasing time of exposure to dc glow discharge and attains a minimum. Thereafter, the contact angle increases slightly to show a small hump before saturating finally at longer times of exposure. The lowering of contact angle is primarily due to the increasing polar component of surface energy. Fourier transform infrared spectroscopy and electron spectroscopy for chemical analysis indicate that increasing polar surface energy is accompanied by increased oxidized functional groups such as C–O and C=O, thus showing increasing O/C ratio with increasing exposure time. Atomic force microscopy shows increasing adhesion force with increasing exposure time, consistent with the observed adhesion energy estimated from 2.04 W contact angle measurement.

１成分電子写真システム現像部におけるトナー帯電量に及ぼす現像ロール表面組成の影響

The effect of surface composition of a development roll (mixture of the acrylic resin and the polyurethane) on the toner charge was investigated. The specific toner charge increased with the content of acrylic resin. The mass of toner layer coated on the development roll also increased with the content of acrylic resin because of the increased adhesion force between the toner and the development roll. The current was passed at the blade, the development roll and the supplying roll during the charging. The direction of current at the blade suggested that the blade worked for the charging to toner particles. On the other hand, the development roll worked for the discharging when the content of acrylic resin was less than 40%, while it worked for charging at the content higher than 40%. The charge distribution of toner particles was wider with increasing the acrylic resin because of the charging effect at the development roll.

Wear rate of vertically grown ZnO nanowires sliding against steel micro-sphere

In this work, ZnO nanowires were grown on Si(1 0 0) wafer and sapphire(0 0 1) substrates using metal-organic chemical vapor deposition (MOCVD). The morphology and crystal structure of ZnO nanowires were evaluated by scanning electron microscopy (SEM) and X-ray diffraction (XRD). The wear characteristics of ZnO nanowires were measured using an atomic force microscopy (AFM) apparatus. A steel micro-sphere (radius of 12 μm) was attached to the end of the AFM cantilever and slid against the ZnO nanowires using low normal load. The wear rate of ZnO nanowires was quantified by comparing the geometrical shape of ZnO nanowires before and after the wear test. Also, the adhesive force between the sphere and the nanowires was measured before and after the wear test. The increase of adhesive force is due to the increase in contact surface after the wear test.

Particle Adhesion and Detachment in Turbulent Flows Including Capillary Forces

The effect of capillary forces on particle adhesion and removal mechanism in turbulent flows is studied. Different detachment theories are used and the increase of adhesion force by the capillary effect is included in the analysis. The criteria for incipient rolling and sliding detachments are evaluated. The sublayer and burst models, which account for the structure of turbulent near-wall flows, are used for evaluating the air velocity condition near the substrate. The critical shear velocities for removing particles of different sizes under different conditions are evaluated, and the results are compared with those obtained in the absence of the capillary force. Comparisons of the model predictions with the available experimental data are also presented.

Time-dependent changes in adhesive force between chondrocytes and silk fibroin substrate

In tissue engineering for cartilage repair using scaffold, initial chondrocyte–material interactions are significantly important for the following cell behaviors such as phenotypic expression and matrix synthesis. Silk fibroin scaffold is considered to be one of the useful materials in/on which chondrocytes can proliferate without dedifferentiating into fibroblast-like cells and can organize a hyaline-like tissue. For the purpose of seeking some useful aspects for designing scaffold, initial adhesive force of chondrocytes to the surface of fibroin substrate was measured by using a lab-made apparatus applying the cantilever beam method. It was found that the adhesive force per unit spreading area of chondrocytes on fibroin substrate had a clear peak between 6 and 12 h after seeding. From the results of immunofluorescence staining for actin and vinculin during this period, it could be thought that an immature formation of actin fibers which was uniquely observed at the periphery of cells attaching to fibroin substrate did not contribute to the increase of adhesive force. Results in this study suggested that surface of the fibroin substrate was gradually covered with some substances which inhibit the adhesion during this period. These cell–material interactions have a possibility to be useful information for designing the adhesive performance of scaffold surface in cartilage regeneration.

The interrelation between adhesion, contact creep, and roughness on the life of gold contacts in radio-frequency microswitches

With repeated actuation, an increasing adhesive force develops between the gold contacts of radio-frequency microswitches until failure eventually occurs by stiction. Detailed characterization of the contact forces and the contact surfaces as a function of actuation cycles for “cold-switched” devices indicates that the increase in adhesive forces in air is attributed to mechanical creep of the polycrystalline gold contacts. The increase in adhesion is observed to be associated with an increase in contact area and depth of contact impression as well as asperity flattening. These morphological observations are related to the propensity for stiction using two nondimensional numbers, the plasticity index ψ and the adhesion parameter θ. Trajectories of the evolution of contact roughness in terms of these two numbers provide insight into the design of contacts to resist stiction.

열차폐 코팅을 위한 지르코니아계 세라믹 소재의 기계적 특성

A gas turbine blade with thermal barrier ceramic coating is operated at high temperature to increase engine efficiency. Recently, thermal barrier characteristics have been improved by advanced coating technology through microstructure control and increase of adhesion force of the coating layer. More advanced coating materials, rare earth zirconate ceramics have been studied for replacing YSZ coatings as thermal barrier coatings. In this study, La₂O₃, HfO₂, CeO₂, Gd₂O₃ and pure or yttria stabilized zirconia were prepared. Microstructure analysis and the evaluation of mechanical properties such as Hertzian indentation and hardness test were performed.

Determination of organophosphorus pesticides in water samples by single drop microextraction and gas chromatography-flame photometric detector

In this paper we have developed single drop microextraction (SDME) with modified 1.00 μl microsyringe, followed by gas chromatography with flame photometric detector (GC-FPD) for determination of 13 organophosphorus pesticides (OPPs) in water samples. By using a 1.00 μl microsyringe the repeatability of drop volume and injection were improved, because of using maximum volume of microsyringe and no dead volume. On the other hand, the modification of needle tip caused increasing cross section of needle tip and increasing adhesion force between needle tip and drop, thereby increasing drop stability and achieving a higher stirrer speed (up to 1700 rpm). The method used 0.9 μl of carbon tetrachloride as extractant solvent, 40 min extraction time, stirring at 1300 rpm and no salt addition. The enrichment factor of this method ranged from 540 to 830. The linear ranges were 0.01–100 μg/l (four orders of magnitude) and limits of detection were 0.001–0.005 μg/l for most of analyte. The relative standard deviation (RSD%) for 2 μg/l of OPPs in water by using internal standard was in the range 1.1–8.6% ( n = 5). The recoveries of OPPs from farm water at spiking level of 1.0 μg/l were 91–104%.

Residence Time, Loading Force, pH, and Ionic Strength Affect Adhesion Forces between Colloids and Biopolymer-Coated Surfaces

Exopolymers are thought to influence bacterial adhesion to surfaces, but the time-dependent nature of molecular-scale interactions of biopolymers with a surface are poorly understood. In this study, the adhesion forces between two proteins and a polysaccharide [Bovine serum albumin (BSA), lysozyme, or dextran] and colloids (uncoated or BSA-coated carboxylated latex microspheres) were analyzed using colloid probe atomic force microscopy (AFM). Increasing the residence time of an uncoated or BSA-coated microsphere on a surface consistently increased the adhesion force measured during retraction of the colloid from the surface, demonstrating the important contribution of polymer rearrangement to increased adhesion force. Increasing the force applied on the colloid (loading force) also increased the adhesion force. For example, at a lower loading force of approximately 0.6 nN there was little adhesion (less than -0.47 nN) measured between a microsphere and the BSA surface for an exposure time up to 10 s. Increasing the loading force to 5.4 nN increased the adhesion force to -4.1 nN for an uncoated microsphere to a BSA surface and to as much as -7.5 nN for a BSA-coated microsphere to a BSA-coated glass surface for a residence time of 10 s. Adhesion forces between colloids and biopolymer surfaces decreased inversely with pH over a pH range of 4.5-10.6, suggesting that hydrogen bonding and a reduction of electrostatic repulsion were dominant mechanisms of adhesion in lower pH solutions. Larger adhesion forces were observed at low (1 mM) versus high ionic strength (100 mM), consistent with previous AFM findings. These results show the importance of polymers for colloid adhesion to surfaces by demonstrating that adhesion forces increase with applied force and detention time, and that changes in the adhesion forces reflect changes in solution chemistry.

Modeling of the Structure of a Bulk Layer

The characteristics of porous layers of a dispersed material have been investigated by the method of computer modeling. A linear growth in the porosity with increase in the adhesive force has been revealed. The statistical distribution functions of the size of pores and their shape have been computed and analyzed for different values of the adhesion forces. The distinctive features of the orientation of pores for different adhesive forces have been noted.