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A solid inclusion is embedded in a soft matrix supported by a rigid substrate. To simulate finger palpation, a spherical indenter exerts a vertical load on the matrix surface, followed by a lateral motion. A deep inclusion first rises close to the surface, dives under the indenter, and emerges from the leeside of the traversing indenter. The inclusion trajectory is essentially symmetric about the axis where the inclusion lies. A shallow inclusion is first pushed sideways, but an instability causes it to jump spontaneously to the rear following an asymmetric path. Such instability is a specific feature in hyperelastic materials. [ABSTRACT FROM AUTHOR]

An ouzo droplet is a multicomponent liquid comprising ethanol, water, and anise oil, each possessing distinct thermophysical properties, volatility, and mutual miscibility. Evaporation leads to the complex physicochemical process of coupled mass and heat transfer, spontaneous emulsification, and liquid–liquid phase separation, known as the ouzo effect. An acoustically levitated ouzo droplet undergoes five characteristic stages of evaporation based on temporal temperature variation. Such levitated droplet shows a significantly longer lifespan upon evaporation because of the thermal isolation in air, as well as a drastic initial cooling. Sessile droplets, on the other hand, have heat transferred from the surroundings via the substrate to replenish latent heat of vaporization. A conductive substrate thus helps the droplet to stay close to the ambience and a shorter lifespan. A rudimentary theoretical model based on dimensional analysis is developed and shows consistency with measurements. [ABSTRACT FROM AUTHOR]

Fingering of an inviscid liquid droplet upon impact on a super-hydrophobic surface is revisited. Generation of coronal fingers is investigated here using a transverse rim instability analysis based on the toroidal curvature of rim, instead of the linear front assumption in the classical Rayleigh-Plateau (R-P) model. The governing equations are formulated from the first principles and solved numerically. For a droplet with a known volume and impact velocity, the model predicts the number of spires upon impact, k. Here k is found to be the largest wave number with a positive growth rate on the droplet rim and is shown to be in the order of (Weber)3/5. The theoretical model is consistent with our water droplet experiments for 60 < We < 160, superseding the R-P prediction. [ABSTRACT FROM AUTHOR]

A solid inclusion is embedded at a depth in a hyperelastic soft matrix resting on a rigid substrate. External compression is applied via an indenter vertical to the substrate, but the loading axis is misaligned with the inclusion. In case of large offset distance, the inclusion dodges the advancing indenter by moving laterally. For small offset, the inclusion moves vertically downward initially but turns abruptly sideways once the indenter reaches a critical depth. The unique behavior of gel under large elastic deformation is investigated by finite element analysis. Southwell subcritical extrapolation method is used to estimate the maximum indentation depth before a lateral displacement of the inclusion becomes inevitable. • An inclusion is embedded in a soft matrix. • Indentation axis is slightly misaligned with the inclusion. • Once indenter reaches a critical depth, inclusion experiences an unstable lateral motion. • Initial nearly symmetric stress field thus becomes asymmetric. [ABSTRACT FROM AUTHOR]

A new Tabor's parameter ? is defined for adhesion-delamination of thin membranes. A small ? corresponds to a thick, small, and stiff membrane under the influence of a long-range weak surface force, as in the Derjaguin-Muller-Toporov (DMT) limit. A large ? corresponds to a thin, large, and flexible membrane under the influence of a short-range strong surface force, as in the Johnson-Kendall-Roberts (JKR) limit. A new adhesion map based on ? is drawn to summarize the "pull-off" events and the delamination trajectory for membranes under mixed stretching-bending deformation. Maps are generated for one- and two-dimensional membranes clamped at the edge. [ABSTRACT FROM AUTHOR]

Abstract: A one-dimensional (1-D) rectangular pre-stressed thin film clamped at two opposite ends is actuated by an electrostatic voltage applied to a pad directly underneath. The pre-stress is allowed to be either tensile or compressive in nature. At a critical applied voltage, the film becomes unstable and makes direct contact with the pad, leading to “pull-in”. An elastic model is constructed to account for the phenomenon over ranges of film–pad gap and residual stress. The results compare favorably with finite element analysis (FEA) in literature and experimental data, and possess distinct advantages over other available closed-form solutions. The model is further extended to a two-dimensional (2-D) axisymmetric diaphragm clamped at the periphery. Interrelationship between bridge–pad gap, residual membrane stress, critical voltage, and pull-in central deflection is derived such that new design criteria can be derived for micro-/nano-electromechanical devices. Implications for nano-structures are also discussed. [Copyright &y& Elsevier]

Abstract: The adhesion of films and coatings to rigid substrates is often measured using blister geometries, which are loaded either by an applied pressure or a central shaft. The measurement will be affected if there are residual stresses that make a contribution to the energy release rate. This effect is investigated using analytical solutions based on the principle of virtual displacements. A geometrically nonlinear finite element analysis is conducted for comparison. Furthermore, the relationships among strain energy release rate, load, deflection, and fracture radius are discussed in detail. Both analytical solutions and numerical results reveal that uniform tensile residual stresses reduce a specimen’s deflection if it experiences plate behavior under small loads. However, this effect becomes negligible when membrane stresses induced by the loading become dominant. [Copyright &y& Elsevier]

The strain energy release rate, G, is derived from first principles and is shown to be consistent with the exact numerical solution by Cotterell and Chen (Int. J. Fract. 86 (1997) 191). Comparison with the classical Rayleigh–Ritz energy method and other published methods shows that the gradual change in blister profile over the entire loading process must be considered for the correct G to be calculated. [Copyright &y& Elsevier]

An accurate closed-form analytical solution for the strain energy release rate for a thin rectangular film loaded by a central line force using the pull-off test is derived in the presence of a tensile residual stress. The theoretical constitutive relation and the strain energy release rate agree very well with two-dimensional nonlinear finite element analysis for the entire deformation regime ranging from bending plate to stretching membrane. Fracture modes for this pull-off test are also investigated based upon the finite element analysis, offering additional insights to the interfacial delamination. [Copyright &y& Elsevier]

Tensile residual stress in a plate or membrane clamped at the perimeter can be measured by either applying a uniform hydrostatic pressure or a central load via a cylindrical punch (with several different loading configurations). Analytical constitutive relations are derived here based on an average membrane stress approximation and are compared to finite element analysis results. The thickness and flexural rigidity of the film are not confined to a small range but will span a wide spectrum. The elastic responses of the blistering films are shown to be linear when the film is thick, relatively rigid, or subjected to a large residual stress, and cubic when the film is thin, flexible, or under a small residual stress. The linear-to-cubic transition is formulated. [Copyright &y& Elsevier]

A new theoretical model is presented for the mechanical response of a thin-walled bio-mimetic microcapsule upon indentation using an atomic force microscope. The membrane is strained by both bending moments and membrane stress in the presence of a tensile pre-stress. When the intrinsic membrane stress is large compared to the local stress around the indentation dimple, the constitutive relation is linear; and when it is small, a cubic relation is deduced. The new theory is rigorously compared to the existing models of: (i) membrane under pure bending by Boulbitch; and (ii) membrane under pure stretching by Yao et al., which are shown to be two limiting cases of our general solution. Published experimental data in literature show that AFM measurement always involves deformation mode of mixed bending and stretching. [Copyright &y& Elsevier]

A new theoretical model was developed for a pull-off adhesion test using an axisymmetric flat punch and a rectangular flat punch adhered to a thin polymer film interface. An elastic solution was derived to portray the mechanical integrity of the thin film. A mechanical energy release rate was calculated numerically. As the punch was pulled away from the adhered film, the film deformed under mixed bending and stretching. Both stiffness and thickness of the film were allowed to vary. The derived solid-film ‘pull-off’ events sharply contrast with the abrupt pull-off in solid–solid adhesion as predicted by the classical JKR theory. [Copyright &y& Elsevier]

The correlation between the mechanical property and the thermotropic transition of the phospholipid bilayer has been recently demonstrated (Chem. Phys. Lipids 110 (2001) 27). However, the role of thermal induced mechanical responses of phospholipid bilayer on the contact mechanics of liposome adhering on a cationic substrate has not been determined. In this study, confocal-reflectance interference contrast microscopy, phase contrast microscopy and contact mechanics modeling are applied to probe the adhesion mechanisms of liposomes in the presence of electrostatic interactions during the thermotropic transition of the lipid bilayer. When temperature increases from 23 to 49 °C at pH 7.4, the degree of liposome deformation (a/R) and adhesion energy of dipalmitoyl-sn-glycero-3-phosphocholine liposome increases by 10% and remains constant, respectively, on 3-amino-propyl-triethoxy-silane (APTES) modified substrate. The extents of increase in these two parameters are highly dependent on the physicochemical properties of the rigid substrate. At pH 4, the adhesion energies above and below the phase transition temperature (Tm) are increased by one order of magnitude due to the formation of the free silanol groups on APTES substrate. In hypotonic condition, the degree of vesicle deformation remains constant and the adhesion energy reduces by 20% during sample heating. Under all conditions, the adhesion energy of the adhering liposome spans a few orders of magnitude against the increase of liposome size as the surface area to volume ratio is maximized in smallest vesicle. [Copyright &y& Elsevier]

The physiochemical properties of phospholipid vesicle, e.g. permeability, elasticity, etc., are directly modulated by the chain-melting transition of the lipid bilayer. Currently, there is a lack of understanding in the relationship between thermotropic transition, mechanical deformation and adhesion strength for an adherent vesicle at temperature close to main phase transition temperature Tm. In this study, the contact mechanics of dimyristoyl-phosphatidylcholine (DMPC) vesicle at the main phase transition are probed by confocal reflectance interference contrast microscopy in combination with phase contrast microscopy. It is shown that DMPC vesicles strongly adhere on pure fused silica substrate at Tm and the degree of deformation as well as the adhesion energy is a decreasing function against the mid-plane diameter of the vesicles. Furthermore, an increase of osmotic pressure at the gel/liquid crystalline phase co-existence imposes insignificant changes in both the degree of deformation and adhesion energy of adherent vesicles when the lipid bilayer permeability is maximized. With the reverse of substrate charge, the mechanical deformation and adhesion strength for larger vesicles (mid-plane diameter >18 μm) are significantly reduced. By monitoring the parametric response of substrate-induced vesicle adhesion during main phase transition, it is shown that the degree of deformation and adhesion energy of adhering vesicle is increased and unchanged, respectively, against the increase of temperature. [Copyright &y& Elsevier]

A letter to the editor is presented in response to the article "Adhesion-delamination mechanics of a presented rectangular film adhered onto a rigid substrate."

A prestressed rectangular film clamped at both ends delaminates from a rigid punch. Based on a thermodynamic energy balance, the delamination mechanics is derived to relate the simultaneous external tensile force applied to the punch, punch displacement, and contact area. Effects of the coupled tensile residual membrane stress and adhesion energy at the punch-film interface are investigated. A “pinch off” (stable shrinking of the contact area to a line) is predicted, contrasting the nonzero “pull-off” radius in a clamped circular film. The model is useful in understanding the behavior of various adhesion-delamination phenomena, especially in one dimensional capacitive microelectromechanical systems radio frequency switches, microstructure network, and nanostructures. [ABSTRACT FROM AUTHOR]

Understanding the impact of climate stressors on photovoltaic (PV) backsheet degradation in real-use conditions is critical to improve the accelerated testing exposures, extend the backsheet lifetime, and increase the confidence in PV reliability. In this work, a total of 33 PV module backsheets were retrieved from six climatic zones worldwide with 2 - 28 years of exposure. These modules included five types of backsheet air-side materials (or outer layer): poly(vinylidene fluoride) (PVDF), poly(tetrafluoroethylene-co-hexafluoropropylene-co-vinylidene fluoride) (THV), poly(vinyl fluoride) (PVF), poly(ethylene terephthalate) (PET), and polyamide (PA). Attenuated total reflection Fourier-transform infrared spectroscopy (ATR-FTIR) was used to identify air-side materials. The degradation induced color change, gloss loss, and chemical material changes analyzed using optical microscopy, differential scanning calorimetry (DSC), scanning electron microscopy (SEM), colorimetry (yellowness index (YI)), and gloss measurements. PVDF, THV, and PVF air-side layer backsheets, in particular PVF, had minimal degradation in the air-side layer appearance and chemical structures after exposure in different climatic zones. The PET air-side backsheets exhibited obvious color increase (22.55 YI units after about 9 years exposure) and the PA/PA/PA backsheets showed large gloss loss (up to 76.4 %) relative to the unexposed backsheets. Severe cracks between cells that penetrated through the entire thickness of backsheets are observed on PA/PA/PA backsheets after 4-6 years of exposure in 6 climatic zones. The current indoor exposure standards were not sufficient to identify this degradation type. However, fluoropolymer based PV backsheets showed lower levels of degradation predictors and increased climatic resistance. Specific samples (PVF) showed little change from baseline after 28 years of outdoor exposure. • Retrieved module backsheet characterization. • Diverse climatic exposure. • Inhomogeneous backsheet degradation. [ABSTRACT FROM AUTHOR]

A spherical inclusion is embedded in a soft gel block. A vertical force is applied on the gel surface by means of a spherical indenter. The loading axis is not aligned with the inclusion but placed at a horizontal offset displacement from the inclusion. The measurement of indentation force and inclusion trajectory are compared to the computational results from two-dimensional (2D) Finite Element Analysis (FEA) simulations. A discernible instability emerges when the indentation reaches a critical depth, in accordance with the Southwell instability theory. The three-dimensional (3D) trajectory shows distinct features that were previously not captured by the 2D FEA simulations. • Cancer tumor in body tissue is modeled as solid spherical inclusion embedded in a soft gel matrix. • Indentation on gel surface leads to unstable lateral motion of an inclusion aligned with the loading axis. • Behavior of off-axis inclusions can be predicted by the classical Southwell instability theory. • Mechanical force on the indenter is consistent with finite element analysis. • A viable model is established for palpation mechanics. [ABSTRACT FROM AUTHOR]

The mechanical deformation of an ideal thin-walled cylindrical shell is investigated in the presence of intersurface interactions with a planar rigid substrate. A Dugdale- Barenblatt-Maugis (DBM) cohesive zone approximation is introduced to simulate the convoluted surface force potential. Without loss of generality, the repulsive component of the surface forces is approximated by a linear soft-repulsion, and the attractive component is described by two essential variables, namely, surface force range and magnitude, which are allowed to vary. The nonlinear problem is solved numerically to generate the pressure distribution within the contact, the deformed membrane profiles, and the adhesion-delamination mechanics, which are distinctly different from the classical solid cylinder adhesion models. The model has wide applications in cell adhesion and nanostructures. [ABSTRACT FROM AUTHOR]

The work of adhesion at the interface of electrospunmembrane andrigid substrate is measured by a shaft-loaded blister test (SLBT).Poly(vinylidene fluoride) (PVDF) were electrospun with an averagefiber diameter of 333 ± 59 nm. Commercial cardboard with inorganiccoating was used to provide a model substrate for adhesion tests.In SLBT, the elastic response PVDF was analyzed and its adhesion energymeasured. The average value of the adhesion work is 206 ± 26mJ/m2. Elastic modulus of electrospun membrane obtainedby SLBT is found to be 23.42 ± 2.69 MPa, which is consistentwith the value obtained from standard tensile tests. The results showSLBT presented a viable methodology for evaluating the adhesion energyof electrospun polymer fabrics. [ABSTRACT FROM AUTHOR]

• Two PET-based backsheets were exposed to indoor UV accelerated weathering. • Single cantilever beam (SCB) tests were used to measure the adhesion in the backsheets. • Both backsheets showed high initial (unweathered) adhesion energies. • After moderate exposure, the polyurethane-based adhesives showed significant adhesion loss. • After high exposure, the PET outer layer showed appreciable UV-induced surface degradation. Delamination between layers in photovoltaic (PV) backsheets is often reported in the literature, causing voids that can collect moisture, diminish module backside heat dissipation, and reduce the backsheet's effectiveness as a physical barrier. While backsheets with weathering-resistant fluoropolymer outer layers have traditionally been used in modules, more recent backsheets using non-fluoropolymer outer layers, such as polyethylene terephthalate (PET), have been developed. These backsheets have shown signs of premature degradation, and their adhesion degradation, in particular, has not been widely studied. In the present work, the single cantilever beam (SCB) adhesion test was used to quantify the adhesion energy in two commercially available PET-based backsheets. To study the effect of minor changes in formulation, the backsheets were obtained from same manufacturer and product line but during different years. To study the effect of environmental variables on adhesion degradation, the backsheets were subjected to artificial weathering at controlled temperature, humidity, and ultraviolet (UV) radiation in an indoor weathering chamber, and the adhesion energy was quantified at several intervals of exposure time. Layering structure, composition, and adhesion failure mode were compared between the backsheets, using Raman and infrared spectroscopy and thermogravimetric analysis. The results show a large difference in initial (unexposed) adhesion energy between the backsheets, despite very similar structures and compositions. Following exposure, adhesion energy dropped significantly, primarily due to thermo-hydrolytic degradation of the polyurethane (PU)-based adhesive layers. Significant UV-induced adhesion degradation of the PET outer layer surface was also observed. The study represents an important step in understanding adhesion degradation in PET-based backsheets, suggesting ways in which adhesion integrity – and, correspondingly, module service life – can be improved. [ABSTRACT FROM AUTHOR]

It has been recently demonstrated that acyl chain mismatch of phospholipid bilayer composed of a binary lipid mixture induces component formation on the lateral plane of the bilayer [Biophys. J. 83 (2002) 1820–1883]. In this report, the contact mechanics of unilamellar vesicles composed of binary dimyristoyl-phosphatidylcholine (DMPC)/dipalmitoyl-phosphocholine (DPPC) mixtures on fused silica and amino-modified substrates is simultaneously probed by confocal-reflectance interference contrast microscopy (C-RICM) and cross-polarized light microscopy during gel to liquid crystalline transition of the lipid bilayer. C-RICM results indicate that the average degree of vesicle deformation for DMPC-rich and DPPC-rich vesicles adhering on fused silica substrate is increased by 30% and 14%, respectively, in comparison with that in pure DMPC and DPPC vesicles. Also, lateral heterogeneity induced by acyl chain mismatch increases the average magnitude of adhesion energy in DMPC-rich and DPPC-rich vesicles of all sizes by 6.4 times and 2.3 times, respectively. Similar modulation of adhesion mechanics induced by carbon chain difference is obtained on amino-modified substrate. Most importantly, the thermotropic transition of the mixed bilayer from gel (below Tm) to fluid phase (above Tm) further exemplifies the effect of acyl chain mismatch on the increases of degree of vesicle deformation and adhesion energy. [Copyright &y& Elsevier]

Adhesion of cells on biomaterial surface is resulted from the complex interplay of specific recognitions and colloidal interactions. Thus understanding the role of electrostatic interactions in bioadhesion may help to elucidate the physiochemical basis of cell signaling pathway on therapeutic devices. In this report, high-resolution reflection interference contrast microscopy, cross-polarized light microscopy and contact mechanics modeling are applied to probe the equilibrium adhesion of giant phospholipid vesicles on 3-amino-propyl-triethoxy-silane coated glass. Simultaneously, the effects of vesicle wall thickness, pH, osmotic stress and surface chemistry on the electrostatic interactions at the membrane–substrate interface are evaluated. The results show that both unilamellar vesicles (ULV) and multilamellar vesicles (MLV) strongly adhere on the cationic substrates at neutral pH. In the presence of electrostatic interactions, ULV is slightly deformed on the substrate as the dimension of its adhesive–cohesive zone is only 6–10% higher than the theoretical value of a rigid sphere with the same mid-plane diameter. The variances of contact angle and capillary length at different locations surrounding MLV are ten times higher than those of ULV. The adhesion energy of ULV with mid-plane diameter of 45 and 20 μm is determined as 3.8×10−12 and 8.6×10−12 J/m2, respectively, from the truncated sphere model. Moreover, the increase of osmotic stress induces irregular pattern in ULV''s adhesion disc and raises the adhesion energy by 10-fold. Finally, the reduction of pH further enhances the electrostatic attractions/repulsions between vesicle surface and cationic or anionic substrates and leads to an increase of adhesion strength. [Copyright &y& Elsevier]

High-resolution reflection interference contrast microscopy (HR-RICM) was developed for probing the deformation and adhesion of phospholipid vesicles induced by colloidal forces on solid surfaces. The new technique raised the upper limit of the measured membrane–substrate separation from 1 to 4.5 μm and improved the spatial resolution of the heterogeneous contact zones. It was applied to elucidate the effects of wall thickness, pH and osmotic stress on the non-specific adhesion of giant unilamellar vesicles (ULV) and multilamellar vesicles (MLV) on fused silica substrates. By simultaneous cross-polarization light microscopy and HR-RICM measurements, it was observed that ULV with the wall thickness of a single bilayer would be significantly deformed in its equilibrium state on the substrate as the dimension of its adhesive–cohesive zone was 29% higher than the theoretical value of a rigid sphere with the same diameter. Besides, electrostatic interaction was shown as a significant driving force for vesicle adhesions since the reduction in pH significantly increased the degree of deformation of adhering ULV and heterogeneity of the adhesion discs. The degree of MLV deformation on the solid surfaces was significantly less than that of ULV. When the wall thickness of vesicle increased, the dimension of contact zone was reduced dramatically due to the increase of membrane bending modulus. Most important, the adhesion strength of colloidal adhesion approached that of specific adhesion. Finally, the increase of osmotic stress led to the collapse of adhering vesicles on the non-deformable substrate and raised the area of adhesive contact zone. To interpret these results better, the equilibrium deformation of adhering vesicle was modeled as a truncated sphere and the adhesion energy was calculated with a new theory. [Copyright &y& Elsevier]

Unidirectional glass fiber reinforced and glass-carbon fiber reinforced epoxy matrix composite samples (% glass to carbon fiber volume ratio 90:10 and 75:25) were subject to two-point bend rupture test in distilled water at 75°C and tension-tension cyclic test in both air and distilled water at 25°C. In the rupture test, while no obvious difference in rupture time was observed at larger deflections, glass--carbon hybrid samples showed prolonged rupture time in comparison to all-glass samples when loaded at 10% maximum deflection. When compared to samples tests in air, cyclic loading in water resulted in shorter fatigue lives for both all-glass and hybrid composite samples. However, hybrid samples showed better environmental fatigue resistance in water than all-glass samples, to 10 7 cycles. By incorporating appropriate amount of carbon fibers in glass fiber composite, long-term performance of glass--carbon hybrid composites under static and dynamic fatigue is substantially enhanced. It is demonstrated by the present study that the intra-ply hybrid approach is effective and economical in improving the durability of fiber reinforced polymer composites for long term applications. [ABSTRACT FROM AUTHOR]

A levitated glycerol droplet supported by an acoustic standing wave, when subject to modulated field at frequency on the order of 150 Hz, behaves as a solid plate and exhibits flexural bending resonance rather than the conventional equatorial star-shape oscillations. Three oscillation modes are observed: seesaw, saddleback, and monkey saddle with the increasing energy levels. The finite element analysis generates droplet shapes consistent with the experimental observation and yields apparent plate flexural rigidity in terms of surface tension and aspect ratio of plate thickness to diameter. High viscosity leads to the plate-like behavior of the droplet. [ABSTRACT FROM AUTHOR]

The width tapered beam method for measuring fracture toughness has been contemplated for use in measuring the adhesion of photovoltaic materials, is promoted by it being a viable method for use directly on modules rather than to engineered test specimens. However, precise determination of crack length is often difficult as failure often involves tendril formation, cavitation voids, and other plastic deformation at the crack front in addition to obfuscation by opaque materials. Because fracture energy varies as the square of crack length, imprecise crack tip length results in large measurement uncertainties. In this work, we develop a method to estimate the crack tip length using the relationship between the applied force and the displacement of the load frame. The crack tip is determined for every data point and can be defined from a calibration curve related to the amount of energy put into the beam, or from a theoretically idealized estimation. Once a calibration curve is set up and the equations programmed, the fracture energy as a function of position on the newly formed crack interface can be accurately estimated. The test additionally provides much easier analysis and insight into the joint failure through more precise knowledge of fracture toughness at each de-bonded area. [ABSTRACT FROM AUTHOR]

An array of gold nano-pillars is fabricated on silicon, before chemical vapor deposited graphene is transferred to the substrate. Intrinsic intersurface attraction pulls the monolayer into intimate contact conforming to the substrate geometry, but the pillars support an array of circular blisters. A simple delamination mechanics model is constructed to extract the materials and interface properties. The graphene-gold interfacial adhesion energy is found to be γ = 450 ± 100 mJ m-2 by measuring the blister dimension. Should the ratio of pillar height to inter-pillar separation falls short of (γ/Eh)1/4 with graphene elastic modulus, E and thickness, h, the blisters stay isolated; otherwise, adjacent blisters coalesce. Critical design guidelines are set for graphene devices. [ABSTRACT FROM AUTHOR]

A nano-cheese-cutter is fabricated to directly measure the adhesion between two freestanding nano-fibers. A single electrospun fiber is attached to the free end of an atomic force microscope cantilever, while a similar fiber is similarly prepared on a mica substrate in an orthogonal direction. External load is applied to deform the two fibers into complementary V-shapes, and the force measurement allows the elastic modulus to be determined. At a critical tensile load, 'pull-off' occurs when the adhering fibers spontaneously detach from each other, yielding the interfacial adhesion energy. Loading-unloading cycles are performed to investigate repeated adhesion-detachment and surface degradation. [ABSTRACT FROM AUTHOR]

We report a technique to characterize adhesion of monolayered/multilayered graphene sheets on silicon wafer. Nanoparticles trapped at graphene-silicon interface act as point wedges to support axisymmetric blisters. Local adhesion strength is found by measuring the particle height and blister radius using a scanning electron microscope. Adhesion energy of the typical graphene-silicon interface is measured to be 151±28 mJ/m2. The proposed method and our measurements provide insights in fabrication and reliability of microelectromechanical/nanoelectromechanical systems. [ABSTRACT FROM AUTHOR]

A microfluidic device was designed to investigate filtration of particles in an electrolyte in the presence of liquid flow. Polystyrene spheres in potassium chloride solution at concentrations of 3–100 mM were allowed to settle and adhere to a glass substrate. A particle free solution at the same concentration was then flushed through the microfluidic channel at 0.03–4.0 mL/h. As the hydrodynamic drag on the adhered particles exceeded the intersurface interaction with the substrate, “pull-off” occurred and the particles detached. Filtration efficiency, α, was shown to a function of both ionic concentration of the liquid medium and flow speed, consistent with a phenomenological model based on the classical DLVO theory. The results elucidates the underlying physics of filtration. [ABSTRACT FROM AUTHOR]

A hyperelastic shell with spherical cap geometry is compressed to a rigid planar substrate. Using Maugis' graphical method and a numerical approach, the quasi-static adhesion-detachment trajectory, the interrelation between applied load, approach distance and contact radius, and the critical pull-off parameters are determined for ranges of materials stiffness, shell thickness, shell depth and interfacial adhesion energy. [ABSTRACT FROM AUTHOR]

A theoretical model is built for a micrometer size cylindrical shell adhering to a rigid surface in the presence of an electrolyte. In the presence of surface electrostatic double layers and van der Waals attraction according to the Derjaguin-Landau-Verwey-Overbeek (DLVO) theory, the shell deforms and settles in either the primary (lmin) or secondary (2min) energy minimum depending on whether it has sufficient energy to overcome the repulsive energy barrier. The adhesion-detachment mechanics are constructed and solved computationally, yielding the relations between applied load, deformed profile, and mechanical stress distribution in the shell. The critical compressive load needed for transition from 2min to lmin is found for several repulsive barrier heights. At a critical pull-off tensile force, shell in the lmin detaches spontaneously at a nonzero contact area, but the one in the 2min detaches smoothly with the contact shrinking to a line contact. The model is relevant to bacterial adhesion in environmental engineering and microelectromechanical systems for microfluidics applications. [ABSTRACT FROM AUTHOR]

Abstract: Macroscopic adhesion–aggregation, floc formation, and subsequent transportation of microorganisms in porous media are closely related to the microscopic behavior and properties of individual cells. The classical Tabor’s parameter in colloidal science is modified to correlate the macroscopic aggregation and microscopic adhesion properties of microorganisms. Seven bacterial strains relevant to wastewater treatment and bioremediation were characterized in terms of their macroscopic aggregation index (AI) using an optical method, and their microscopic coupled adhesion and deformation properties using atomic force microscopy (AFM). Single cells were indented to measure the range and magnitude of the repulsive–attractive intersurface forces, elastic modulus, thickness and density of the cellular surface substances (CSS). The strong correlation suggests that cost and time effective microscopic AFM characterization is capable of making reliable prediction of macroscopic behavior. [Copyright &y& Elsevier]

Abstract: Adhesion of a pre-stressed silicone rubber film to a planar graphite surface was investigated by a new cylindrical punch method. A homemade apparatus was constructed to meet force and displacement resolutions of 0.1μN and 10nm. When the punch approached the intersurface force range across the punch-film gap, the film jumped into contact at “pull-in”. Upon unloading, once the tensile load reached a threshold, a spontaneous delamination occurred at “pull-off” with a non-zero contact circle. A theoretical model was constructed based a simple energy balance. The new method can be used to characterize an adhesion interface between a pre-stressed free-hanging film and a rigid substrate. [Copyright &y& Elsevier]

Abstract: The elastic properties and adhesion of a thin silicone rubber membrane have been characterized. An effective instrumentation embodying a video-enhanced microscope, which meets force and displacement resolution of and 10nm, was developed. It provides the capability of simultaneously measuring both the applied force and the resultant displacement of the thin polymer membrane. A linear theoretical elastic solution was applied to quantitatively interpret the measured central deflection of the membrane under a circular concentrical load. Young''s modulus of the membrane can be easily determined once the applied force and the central deflection, together with the essential dimensions, are known. The membrane jumped into an adhesion contact when the punch approached the range of the inter-surface force across the punch-membrane gap. A pull-off event was observed at a nonzero contact circle when the tensile load reached a critical threshold. The experiment is basically consistent with a theoretical model based on linear elasticity and an energy balance. The new method can be used to measure mechanical behavior of prestressed ultra-thin biomembranes and thin walled biocapsules with a residual stress. [Copyright &y& Elsevier]

A mechanistic model is constructed to account for colloidal filtration by incorporating fundamental intersurface forces between individual particle and collector, geometry and elastic properties of bacteria / particles, and flowrate of the electrolytic medium. Particle adhesion on the collector surface is derived from the DLVO theory based on electrostatic double layers and van der Waals attraction, while particle detachment depends on the hydrodynamic shear. Filtration efficiency, α, of a conventional packed column is estimated by numerically solving the governing convection-diffusion equation, and is shown experimentally dependent on both ionic concentration and flowrate of the electrolyte contrasting the classical colloid filtration theory. Model bacterial strains of Aeromonas punctata and Raoultella ornithinolytica were investigated using a conventional packed column test and a homemade microfluidic device. Their behavior were shown to be consistent with the model. [ABSTRACT FROM AUTHOR]

Photovoltaic backsheets are exposed to harsh outdoor weathering conditions throughout their service lives that can compromise their protective function, through adhesive debonding between their constituent layers and between the backsheet and the module. A large-scale study on adhesive degradation was conducted on 37 field-exposed modules, that spanned 19 different module manufacturers, that were deployed among six Köppen–Geiger climatic zones, and that were fielded between 0 and 28 years. Six outer layer polymer classes were identified among the backsheets: polyamide (PA), polyethylene terephthalate (PET), polyvinyl fluoride (PVF), polyvinylidene fluoride (PVDF), fluoroethylene vinyl ether copolymer (FEVE), and tetrafluoroethylene hexafluoropropylene vinylidene fluoride copolymer (THV). Two adhesion tests were used to measure the adhesive strength: the wedge test and the width-tapered single-cantilever beam (SCB) test. Adhesion energies were compared across exposure time and Köppen–Geiger climatic zone. Many of the PET-, PVF-, and PVDF-based backsheets experienced degradation of the adhesive layer between the backsheet outer and core layers. A consistent trend of decreasing adhesion energy with exposure time was observed in five out of the six backsheet types. Trends among adhesion energy and climatic zone, while expected, were not observed, possibly due to broad ranges in temperature, humidity, and precipitation defining Köppen–Geiger climatic zones. The cantilever beam measurements produced an upper cutoff of approximately 100 J/m2, above which no modules exhibited field delamination. The results are part of a two-part study quantifying adhesion in both field-weathered and indoor-exposed PV backsheets. • Thirty-seven (37) PV modules were retrieved from various regions around the world • Two adhesion tests were used to characterize backsheet adhesion • Adhesion energy decreased with number of years of field exposure • Backsheets with adhesive tie layers often showed failure in an adhesive layer • Modules with adhesion energies greater than 100 J/m2 showed no field delamination [ABSTRACT FROM AUTHOR]

Uptake of cytotoxic drugs by typical tumor cells is limited by the dense dendritic network of oligosaccharide mucin chains that forms a mechanical barrier. Atomic force microscopy is used to directly measure the force needed to pierce the mucin layer to reach the cell surface. Measurements are analyzed by de Gennes' steric reputation theory. Multidrug resistant ovarian tumor cells shows significantly larger penetration load compared to the wide type. A pool of pancreatic, lung, colorectal, and breast cells are also characterized. The chemotherapeutic agent, benzyl-α-GalNac, for inhibiting glycosylation is shown to be effective in reducing the mechanical barrier. [ABSTRACT FROM AUTHOR]

Photovoltaic (PV) backsheets provide critical moisture, mechanical, and electrical insulation to the backside of PV modules, but their continued functionality depends upon their ability to remain well adhered over years of harsh environmental exposure. A study of adhesive strength was conducted on several PV backsheet types exposed to indoor accelerated weathering. Two adhesion tests – the wedge test and single cantilever beam test – were used to measure adhesion energy in four backsheets: two with fluoropolymer-based outer (airside) layers – polyvinyl fluoride (PVF), polyvinylidene fluoride (PVDF) – and two with non-fluoropolymer-based outer layers–polyamide (PA) and polyethylene terephthalate (PET). The effects of changes in temperature, ultraviolet (UV) irradiance, relative humidity, and a periodic water spray were studied. The PET-, PVF- and PVDF-based backsheets all showed instances of debonding in an adhesive layer, which is commonly reported. For the PA-, PET-, and PVDF-based backsheets, adhesion energy dropped fairly rapidly with exposure, reaching very low levels by 4000 h. The PVF-based backsheet was relatively robust to weathering. Pull-off of an outer chalking layer in the PA- and PET-based backsheets suggested a sensitivity to UV. Adhesion in these two backsheets was also highly sensitive to changes in moisture level. Changes in UV irradiance and temperature did not show a statistically significant effect on adhesion loss for the exposure levels used. The present work is part of a two-part adhesion study on both field-weathered and indoor-exposed backsheets, and forms a basis for understanding adhesion degradation across a variety of backsheet types and degradation factors. • Four indoor-exposed backsheet types were adhesion-tested using two different methods. • Adhesion in the PVF-based backsheet was relatively stable. • The PA-, PET- and PVDF-based backsheets exhibited substantial decrease after 4000 hours. • The PA- and PET-based backsheets exhibited sensitivity to changes in moisture level. • The PET-, PVF-, and PVDF-based backsheets all exhibited debonding in an adhesive layer. [ABSTRACT FROM AUTHOR]

Suspended single-walled carbon nanotubes (SWCNTs) offer unique functionalities for electronic and electromechanical systems. Due to their outstanding flexible nature, suspended SWCNT architectures have great potential for integration into flexible electronic systems. However, current techniques for integrating SWCNT architectures with flexible substrates are largely absent, especially in a manner that is both scalable and well controlled. Here, we present a new nanostructured transfer paradigm to print scalable and well-defined suspended nano/microscale SWCNT networks on 3D patterned flexible substrates with micro- to nanoscale precision. The underlying printing/transfer mechanism, as well as the mechanical, electromechanical, and mechanical resonance properties of the suspended SWCNTs are characterized, including identifying metrics relevant for reliable and sensitive device structures. Our approach represents a fast, scalable and general method for building suspended nano/micro SWCNT architectures suitable for flexible sensing and actuation systems. [ABSTRACT FROM AUTHOR]