Adhesion of nonplanar wrinkled surfaces

Topological patterns on polymer surfaces can significantly alter and control adhesion. In this study, the effect of surface wrinkles on a spherical surface on adhesion has been studied. Surface wrinkling induced by swelling of a crosslinked polydimethylsiloxane elastomer constrained by a stiff, thin surface layer (silicate) is used to produce topographic features of various length scales over a large curved area. By controlling the properties of the stiff layer and the applied strain conditions, surface wrinkles of varying amplitude and wavelength are obtained. The effect of wrinkle morphology on adhesion is quantified, and the results display a transition from enhancement of adhesion to decrease depending upon wrinkle dimensions. A simple phenomenological model is proposed that describes the change of adhesion behavior as a function of wrinkle morphology. Our results provide a critical understanding toward tuning the adhesion behavior of nonplanar surfaces consisting of periodic topographic structures. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2011     

Adhesion forces between wetted solid surfaces

We investigate in this paper the influence of wetting films on the adhesion forces between macroscopic solid surfaces connected by a liquid bridge. We show that the capillary forces are dependent on the interactions governing the wetting layers, and that those interactions may be determined from the measurement of the capillary force in the presence of a condensable vapor. We illustrate those results with a surface force apparatus experiment where the capillary force between high-energy surfaces is measured for different liquid pressures.     

Adhesion properties of uric acid crystal surfaces

Two key steps in kidney stone formation--crystal aggregation and attachment to renal tissues--depend on the surface adhesion properties of the crystalline components. Anhydrous uric acid (UA) is the most common organic crystalline phase found in human kidney stones. Using chemical force microscopy, the adhesion force between various functional groups and the largest (100) surface of UA single crystals was measured in both aqueous solution and model urine. Adhesion trends in the two solutions were identical, but were consistently lower in the latter. Changes in the solution ionic strength and pH were also found to affect the magnitude of the adhesion. UA surfaces showed the strongest adhesion to cationic functionalities, which is consistent with ionization of some surface uric acid molecules to urate. Although hydrogen-bonding and van der Waals interactions are usually considered to be dominant forces in the association between neutral organic compounds, this work demonstrates that electrostatic interactions can be important, particularly when dealing with weak acids under certain solution conditions.     

Adhesion of Pseudomonas fluorescens on magnetic surfaces

The adhesion of Pseudomonas fluorescens (ATCC 700830) to perpendicularly polarized magnetic surfaces was recently discovered. The findings have found that the magnetic free surfaces from different magnetic polarities have different profound effects on the P. fluorescens bacterial adhesion to its surfaces. These phenomena can be explained by the surface magnetic effect, which was found to affect the surface free energy. An in situ experiment, by contrast microscopy and under static conditions, was conducted to determine the influence of magnetic surfaces, that are polarized under different external magnetizing field strengths, on bacterial adhesion. The effect of different magnetic polarities on the surface free energy has also been investigated.     

Adhesion of amphipathic molecules to solid surfaces

Summary Oil/water contact angles, coefficient of friction and electron diffraction have been used to study the adsorption of three long chain surface-active substances (a fatty acid, a sulphate and a substituted amine, from aqueous solution on to electropolished copper, aluminium and iron. According to the p_H of the solution, the adsorption occurs by one of the following processes (a) physical adsorption, (b) chemisorption, (c) adherence of a precipitate, (d) sensitised adsorption to form a mixed film. Certain applications e.g. lubrication and the prevention of fretting corrosion, are discussed in relation to the structure and rate of adsorption of the four types of film. The first requirement for an efficient lubricant film is the chemisorption of the long chain compound as a basic metal soap. The film is considerably strengthened by subsequent adsorption of a less polar compound, such as cholesterol, by process (d). A suitable vehicle for the two compounds is an oil/water emulsion.Electron diffraction has been used to determine the physical and chemical nature of the electropolished metal surfaces. Adsorbed monolayers can only be detected on extremely smooth surfaces. A new technique is described for depositing insoluble monolayers on reactive metals, which avoids the roughening of the metal surface experienced in the normal Langmuir-Blodgett method.

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Zusammenfassung Randwinkel öl-Wasser, Reibungskoeffizient und Elektronenstrahlbeugung wurden benutzt zum Studium der Adsorption dreier langkettiger Substanzen (eine Fettsäure, ein Sulfat und ein substituiertes Amin) aus wäßriger Lösung heraus auf elektropoliertes Kupfer, Aluminium und Eisen. Entsprechend dem p_H-Wert der Lösung geschieht die Adsorption durch einen der folgenden Prozesse:a) Physikalische Adsorption, b) Chemisorption, c) Haftung eines Niederschlags und d) sensibilisierte Adsorption unter Bildung eines Mischfilms.Einige Anwendungen, z. B. Schmierung und die Verhinderung von Reibungskorrosion, wurden unter BerÜcksichtigung der Struktur und der Adsorptionsgeschwindigkeit der vier genannten Typen von Adsorptionsschichten diskutiert. Die erste Bedingung fÜr wirksame Schmierung ist die Chemisorption der langkettigen Substanz als basische, metallorganische VerdÜnnung (Seife). Der erhaltene Adsorptionsfilm erfährt eine beachtliche Verfestigung durch nachfolgende Adsorption (nach dem Prozeß d) einer schwächer polaren Substanz, wie des Cholesterols. Ein brauchbarer Träger fÜr beide Komponenten ist eine öl-Wasser-Emulsion.Zur Aufklärung der chemischen und physikalischen Eigenschaften der elektropolierten Metalloberflächen wurde die Elektronenstrahlbeugung eingesetzt. Adsorbierte Monoschichten können nur auf extrem ebenen Oberflächen beobachtet werden. Zur Verhinderung der Aufrauhung von Metalloberflächen, wie sie von der Langmuir-Blodgett-Methode her bekannt ist, wurde eine neue Auftragungstechnik fÜr unlösliche Monoschichten auf reaktionsfähige Metalloberflächen entwickelt.

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This work was carried out during the tenure of Consolidated Zinc Studentships at Trinity Hall, Cambridge, on the part of two of the authors (R. B. W. & J. A. S.). Further financial support was provided by Almin Limited and C. S. I. R. O. (Australia).     

Adhesion contact dynamics of fibroblasts on biomacromolecular surfaces

Biomacromolecules like gelatin and chitosan have emerged as highly versatile biomimetic coatings for applications in tissue engineering. The elucidation of the interfacial kinetics of cell adhesion on biomacromolecular surfaces will pave the way for the rational design of chitosan/gelatin-based systems for cell regeneration. Biomacromolecular ultra-thin films, chemically immobilized on fused silica are ideal experimental models for determining the effect of surface properties on the biophysical cascades following cell seeding. In this study, confocal reflectance interference contrast microscopy (C-RICM), in conjunction with phase contrast microscopy and fluorescence confocal microscopy, was applied to detect the adhesion contact dynamics of 3T3 fibroblasts on chitosan and gelatin ultrathin films. X-ray photoelectron spectroscopy (XPS) confirmed the immobilization of chitosan or gelatin on the silanized glass surface. Both the initial cell deformation rate and the change of two-dimensional spread area of the 3T3 fibroblasts are higher on gelatin-modified surfaces than on chitosan surfaces. The steady-state adhesion energy of 3T3 fibroblasts on gelatin film is three times higher than that on chitosan film. Immuno-staining of actin further demonstrates the different organization of cytoskeleton, likely induced by the change in cell signaling mechanism on the two biomacromolecular surfaces. The better attachment of 3T3 fibroblast to gelatin is postulated to be caused by the presence of adhesive domains on gelatin.     

Antibody-based surfaces: rapid characterization using two complementary colorimetric assays

Finding a general solution for optimizing the grafting of antibody on solid surfaces is difficult due to the variety of material, grafting principles and chemistries or surface formats available (beads, microplates, fibers, etc.). Pre-screening methods able to assess grafting efficiency (GE) and specific activity (SA) are required. In this context, we present here two colorimetric assays that can be used on a wide variety of surface format, chemistry, etc. The first one, ADECA (Amino Density Estimation by Colorimetric Assay) allows a rapid estimation of grafted antibodies and allows calculating the GE. The second one, A₂HRP (Antibody Anti-HorseRadish Peroxidase) provides a measure of the amount of active antibody, which, combined to ADECA, is used to determine the SA of grafted antibody. Analytical parameters (limit of detection, repeatability, linearity, etc.) of these two colorimetric assays are presented. Using two commercially available microplates, we demonstrated that, when used in parallel, these rapid and sensitive methods are well adapted to pre-screening of antibody grafting performances.     

Adhesion of alumina surfaces through confined water layers containing various molecules

When two surfaces confine water layers between them at the nanoscale, the behavior of these confined water molecules can deviate significantly from the behavior of bulk water, and it could reflect on the adhesion of such surfaces. Thus, the aim of this study is to assess the role of confined water layers on the adhesion of hydrophilic surfaces and how sensitive this adhesion is to the presence of contaminants. Our methodology used under water AFM force measurements with an alumina-sputtered sphere-tipped cantilever and a flat alumina single crystal and then added fractions of ethanol, dimethylformamide, formamide, trimethylamine, and trehalose to water as contaminants. Such solutions were designed to illuminate the influences of dielectric constant, molecular size, refractive index, and number of hydrogen bonds from donors and acceptors of solutes to water. Apart from very dilute solutions of dimethylformamide, all solutions decreased the ability of confined water to give adhesion of the alumina surfaces. The predicted theoretical contribution of van der Waals and electrostatic forces was not observed when the contaminants distorted the way water organizes itself in confinement. The conclusion was that adhesion was sensitive mostly to the hydrogen-bonding network within water layers confined by the hydrophilic alumina surfaces.     

Adhesion between graphite and modified polyester surfaces: a theoretical study

This study examines the adhesion of graphite to functionalized polyester surfaces using a range of qualitative and quantitative measures of theoretical adhesion. Modifications to the polyester surfaces include the addition of hydroxyl, carboxyl, or fluorine substituents with coverages of 0.4 and 0.9 groups per nm(2). In each case, the introduction of substituents to the surface of the polyester was calculated to lead to reduced adhesion to graphite. Effects of surface relaxation on adhesion are studied by employing different simulation protocols. The theoretical results suggest one mechanism to reduce adhesion to carbonaceous solids is to increase atomic roughness using strongly hydrophilic or alternatively strongly hydrophobic substituents.     

Adhesion of single polyelectrolyte molecules on silica, mica, and bitumen surfaces

In a recent study (Energy Fuels 2005, 19, 936), a partially hydrolyzed polyacrylamide (HPAM) was used as a process aid to recover bitumen from oil sand ores. It was found that HPAM addition at the bitumen extraction step not only improved bitumen recovery but also enhanced fine solids settling in the tailings stream. To understand the role of HPAM, single-molecule force spectroscopy was employed for the first time to measure the desorption/adhesion forces of single HPAM molecules on silica, mica, and bitumen surfaces using an atomic force microscope (AFM). Silicon wafers with an oxidized surface layer and newly cleaved mica were used, respectively, to represent sand grains and clays in oil sands. The force measurements were carried out in deionized water and in commercial plant process water under equilibrium conditions. The desorption/adhesion forces of HPAM obtained on mica, silica, and bitumen surfaces were approximately 200, 40, and 80 pN in deionized water and approximately 100, 50, and 40 pN in the plant process water, respectively. The measured adhesion forces together with the zeta potential values of these surfaces indicate that the polymer would preferentially adsorb onto clay surfaces rather than onto bitumen surfaces. It is the selective adsorption of HPAM that benefits both bitumen recovery and tailings settling when the polymer was added directly to the bitumen extraction process at an appropriate dosage.     

Adhesion and friction studies of Au nanoparticle‐textured surfaces with colloidal tips

Surface roughness plays an important role in affecting the adhesive force and friction force in microelectromechanical systems (MEMS)/nanoelectromechanical systems (NEMS). One effective approach of reducing adhesion and friction of contacting interfaces is to create textured surface, which is especially beneficial for MEMS'/NEMS' production yield and product reliability. In this article, we present a convenient method to fabricate the nano‐textured surfaces by self‐assembling Au nanoparticles (NPs) on the silicon (100) surfaces. The nanoparticle‐textured surfaces (NPTS) with different packing density and texture height were prepared by controlling the assembling time and the size of Au NPs. The morphologies and chemical states of NPTS were characterized by atomic force microscope (AFM), field emission scanning electron microscope, and XPS. The adhesion and friction on the NPTS were studied by AFM with colloidal tip. The results show that the nano‐textured surfaces have effectively reduced adhesive force and friction force compared with the 3‐aminopropyl trimethoxysilane self‐assembled monolayer surfaces. The lowered adhesion and friction were attributed to the reduced real area of contact between NPTS and colloidal tip. The adhesion and friction of the NPTS are varying with the texture packing density and dependent on both the texture height and asperities spacing, which are related to the size and coverage ratio of NPs on surfaces. Copyright © 2011 John Wiley & Sons, Ltd.     

Adhesion and friction force coupling of gecko setal arrays: implications for structured adhesive surfaces

The extraordinary climbing ability of geckos is partially attributed to the fine structure of their toe pads, which contain arrays consisting of thousands of micrometer-sized stalks (setae) that are in turn terminated by millions of fingerlike pads (spatulae) having nanoscale dimensions. Using a surface forces apparatus (SFA), we have investigated the dynamic sliding characteristics of setal arrays subjected to various loading, unloading, and shearing conditions at different angles. Setal arrays were glued onto silica substrates and, once installed into the SFA, brought toward a polymeric substrate surface and then sheared. Lateral shearing of the arrays was initiated along both the "gripping" and "releasing" directions of the setae on the foot pads. We find that the anisotropic microstructure of the setal arrays gives rise to quite different adhesive and tribological properties when sliding along these two directions, depending also on the angle that the setae subtend with respect to the surface. Thus, dragging the setal arrays along the gripping direction leads to strong adhesion and friction forces (as required during contact and attachment), whereas when shearing along the releasing direction, both forces fall to almost zero (as desired during rapid detachment). The results and analysis provide new insights into the biomechanics of adhesion and friction forces in animals, the coupling between these two forces, and the specialized structures that allow them to optimize these forces along different directions during movement. Our results also have practical implications and criteria for designing reversible and responsive adhesives and articulated robotic mechanisms.     

Transferring complementary target DNA from aqueous solutions onto solid surfaces by using affinity microcontact printing

In this paper, we report a method of transferring complementary target DNA from an aqueous solution onto a solid surface by using affinity microcontact printing. In this approach, the probe DNA is first immobilized on the surface of an aminated poly(dimethylsiloxane) (PDMS) stamp. After a complementary target DNA hybridizes with the probe DNA on the stamp surface, the PDMS stamp is printed on an aminated glass slide. By using fluorescent microscopy, we show that only complementary target DNA, but not noncomplementary DNA, can be captured onto the surface of the stamp and then transferred to the aminated glass slide. The transfer of DNA can be attributed to the stronger electrostatic attraction between DNA and amine groups compared to the hydrogen bonds between the hybridized DNA molecules. We also investigate several factors that may influence the transfer of DNA, such as the surface density of amine groups, hybridization conditions, and contamination from unreacted PDMS monomers.     

Adhesion of bioinspired micropatterned surfaces: effects of pillar radius, aspect ratio, and preload

Inspired by biological attachment systems, micropatterned elastomeric surfaces with pillars of different heights (between 2.5 and 80 microm) and radii (between 2.5 and 25 microm) were fabricated. Their adhesion properties were systematically tested and compared with flat controls. Micropatterned surfaces with aspect ratios above 0.5 were found to be more compliant than flat surfaces. The adhesion significantly increases with decreasing pillar radius and increasing aspect ratio of the patterned features. A preload dependence of the adhesion force has been identified and demonstrated to be crucial for obtaining adhesives with tunable adherence.     

Adhesion forces between functionalized latex microspheres and protein-coated surfaces evaluated using colloid probe atomic force microscopy

Proteins are important in bacterial adhesion, but interactions at molecular-scales between proteins and specific functional groups are not well understood. The adhesion forces between four proteins [bovine serum albumin (BSA), protein A, lysozyme, and poly-d-lysine] and COOH, NH2 and OH-functionalized (latex) colloids were examined using colloid probe atomic force microscopy (AFM) as the function of colloid residence time (T) and solution ionic strength (IS). For three of the proteins, OH-functionalized colloids produced higher adhesion forces to proteins (2.6-30.5 nN; IS=1 mM, T=10s) than COOH- and NH2-functionalized colloids (1.6-6.8 nN). However, protein A produced the largest adhesion force (8.1+/-1.0 nN, T=10 s) with the COOH-functionalized colloid, demonstrating the importance of specific and unanticipated protein-functional group interactions. The NH2-functionalized colloid typically produced the lowest adhesion forces with all proteins, likely due to repulsive electrostatic forces and weak bonds for NH2-NH2 interactions. The adhesion force (F) between functionalized colloids and proteins consistently increased with residence time (T), and data was well fitted by F=ATn. The constant value of n=0.21+/-0.07 for all combinations of proteins and functionalized colloids indicated that water exclusion and protein rearrangement were the primary factors affecting adhesion over time. Adhesion forces decreased inversely with IS for all functional groups interacting with surface proteins, consistent with previous findings. These results demonstrate the importance of specific molecular-scale interactions between functional groups and proteins that will help us to better understand factors colloidal adhesion to surfaces.     

Adhesion of Cryptosporidium parvum and Giardia lamblia to solid surfaces: the role of surface charge and hydrophobicity

Adhesion of Cryptosporidium parvum and Giardia lamblia to four materials of different surface charge and hydrophobicity was investigated. Glass beads were used with and without three polymer coatings: aminosilines (A0750), fluorosilines (T2494), an amino cationic polymer. Surface charge density and hydrophobicity of the beads were characterized by measuring the zeta potential (ZP) and the contact angle, respectively. Adhesion was derived from batch experiments where negatively charged (oo)cysts were mixed with the beads and recovery was determined by counting (oo)cysts remaining in suspension using a flow cytometer. Experimental results clearly show that adhesion to solid surfaces of C. parvum is different from G. lamblia. Adhesion of C. parvum to positively charged, hydrophilic beads (82% recovery relative to control) indicated that surface charge was the more important factor for C. parvum, dominating any hydrophobic effects. Adhesion of G. lamblia cysts to negatively charged, hydrophobic beads (0% recovery relative to control) indicated that although hydrophobicity and surface charge both played a role in the adhesion of G. lamblia to solid surfaces, hydrophobicity was more important than surface charge.     

Adhesion

Ohne Zusammenfassung