Measurement Of Adhesion Strength Research Articles

Voltage activation of poly (ethylene glycol) diacrylate

Free radical polymerization of acrylate resins may be initiated by light or heat, but a direct electronic mode of activation is missing. Voltage activated free-radical polymerization would address this limitation if suitable electronic initiators are available. Herein, a selection of initiators and electrolytes investigate electronic initiation of diacrylate resins. Electrochemistry and rheometry are combined in a custom electrorheometer towards the evaluation of relevant structure property relationships. Viscoelastic material properties are measured as a function of voltage, chemical initiator, cumulative charge, and electrolyte. Upon cathodic activation, liquid to solid transitions with a maximum shear modulus of 139 kPa is observed while anodic activation failed to initiate gelation. Storage modulus and adhesion strength measurements demonstrate that voltage activation of acrylate resins is feasible, but further improvements in increasing crosslinking kinetics are needed before industrial applicability.

Sliding wear behaviour of thermally sprayed WC–20Cr3C2–7Ni and La2O3composite coatings

In this paper, the sliding wear behaviour of WC–20Cr3C2–7Ni and lanthanum (III) oxide (La2O3) composite coating is investigated. The influence of lanthanum (III) oxide is evaluated by varying its proportion (1, 2 and 3 wt%) in WC–20Cr3C2–7Ni coating material. The high-velocity oxy-fuel (HVOF) technique is used to deposit the coatings on AISI 1020 carbon (C) steel. The mechanical strength and metallurgical quality of the deposit were confirmed by microhardness, adhesive strength and porosity measurements; scanning electron microscopy; and X-ray diffractometry. Further, the sliding wear behaviour of the composite coating is tested on pin-on-disc apparatus with silicon carbide (SiC) as counter material at room temperature. From the investigation, it was found that 2% lanthanum (III) oxide in WC–20Cr3C2–7Ni coating achieved good adhesive strength with minimum wear rate. Addition of lanthanum (III) oxide in WC–20Cr3C2–7Ni prevented the coating from undergoing boundary segregation, crack propagation and grain refinement. Abrasion and ploughing are the common wear mechanisms observed in worn surfaces.

Optimizing The Hot-Press Procedure of High-Temperature Proton Exchange Membrane Fuel Cells for Adhesion Strength and Conductivity

As society considers alternatives to energy systems based on fossil fuel combustion, high-temperature proton exchange membrane (HT-PEM) fuel cells may play an important role in our future energy and transportation portfolio. When compared to low-temperature proton exchange membrane (LT-PEM) fuel cells, HT-PEM technology offers enhanced electrode kinetics, simplified water management, and most notably increased tolerance to fuel impurities such as carbon monoxide. However, compared to more conventional LT-PEM systems, less is known about the durability, performance, and fabrication of HT-PEM materials. Comprised of multiple layers, the membrane electrode assembly (MEA) is a fuel cell’s central component. In a fabrication process similar to LT-PEM MEAs, the proton-conducting membrane, electrodes, gas diffusion layers and sub gaskets are usually hot-pressed together. The parameters surrounding the hot-pressing operation can have a significant impact on the ultimate performance of the fuel cell, in addition to influencing process reliability and repeatability. In the current research, measurements of MEA thickness, impedance, and adhesion strength were obtained for samples over a range of conditions to optimize for the most suitable processing parameters. Testing in this study quantified the effects of hot-press time, temperature and pressure, within ranges of 1-10 minutes, 140 – 200oC, and 7.7 – 92.7 MPa (1120 – 13,400 psi), respectively. After hot pressing, the MEA samples were tested for resistance with a 1260a Solartron impedance gain phase analyzer in tandem with a Solartron Ametek 12962a sample holder, and with a Scott internal bond tester for adhesion strength. Based on the results of these tests the optimal hot-press parameters were established, two 45.2 cm2 MEA were built and tested for performance with post-mortem analysis conducted utilizing scanning electron microscopy (SEM) coupled with energy dispersive X-ray spectroscopy (EDX). These measurements enabled interrogation of potential sources of conductivity loss associated with material layer delamination and/or dehydration of phosphoric acid in the polybenzimidazole (PBI) membrane. Figure 1 shows the effect of hot-pressing time and pressure on the resistance of MEA samples for one representative temperature condition. In this case, all tests were conducted at 140oC and the resulting material assembly was allowed to cool to room temperature in a nitrogen glove box prior to executing resistance measurements (i.e., inverse of conductivity). Each point in Figure 1 represents a single hot-pressed sample, with each sample undergoing three consecutive measurements that were then averaged; standard deviations of triplicate measurements ranged from 0.1 to 3.6%. Our results have demonstrated that the optimal conditions for MEA hot-pressing for the HT-PEM system are around 170oC and 23.1 MPa for 5 minutes. Research is ongoing to evaluate the impact of hot-pressing conditions on fuel cell performance and durability with both hydrogen and reformate fuels. Figure 1 – Selected measurements of HT-PEM resistance with variation of hot-press time and pressure at 140oC Figure 1

Superhydrophobic versus SLIPS: Temperature dependence and the stability of ice adhesion strength

HypothesisIce adhesion to solids, being affected by the ice/solid intermolecular interactions and structure of ice surface layer is dependent on temperature, and ice surface layer equilibration time. ExperimentsA new centrifugal method of shear ice adhesion strength measurement with accurate temperature control on each stage from ice formation on test surfaces to the adhesion measurement is applied to study ice adhesion to superhydrophobic and slippery surfaces. The determinative advantage of the developed method is related to monitoring in one experiment the ice detachment from numerous samples and accurate measuring the rotation frequency for each ice detachment. FindingsThe following findings will be discussed.1.Strong temperature dependence of an ice adhesion strength to superhydrophobic and slippery surfaces.2.A decrease in the ice adhesion strength to a rough surface during prolonged ice exposure at a given temperature.3.The delayed spontaneous detachment of ice from the superhydrophobic surface under prolonged action of shear stresses notably lower than those leading to instantaneous detachment.4.Fast degradation of a slippery surface with an increase in ice adhesion strength if the infusing liquid is not replenished before each measurement.

A Bacteria and Cell Repellent Zwitterionic Polymer Coating on Titanium Base Substrates towards Smart Implant Devices.

Biofouling and biofilm formation on implant surfaces are serious issues that more than often lead to inflammatory reactions and the necessity of lengthy post-operation treatments or the removal of the implant, thus entailing a protracted healing process. This issue may be tackled with a biocompatible polymeric coating that at the same time prevents biofouling. In this work, oxygen plasma-activated silanized titanium substrates are coated with poly(sulfobetaine methacrylate), a zwitterionic antibiofouling polymer, using photopolymerization. The characterization of polymer films includes FT-IR, AFM, and adhesion strength measurements, where adhesion strength is analyzed using a cylindrical flat punch indenter and water contact angle (WCA) measurements. Both cytotoxicity analysis with primary human fibroblasts and fluorescence microscopy with fibroblasts and plaque bacteria are also performed is this work, with each procedure including seeding on coated and control surfaces. The film morphology obtained by the AFM shows a fine structure akin to nanoropes. The coatings can resist ultrasonic and sterilization treatments. The adhesion strength properties substantially increase when the films are soaked in 0.51 M of NaCl prior to testing when compared to deionized water. The coatings are superhydrophilic with a WCA of 10° that increases to 15° after dry aging. The viability of fibroblasts in the presence of coated substrates is comparable to that of bare titanium. When in direct contact with fibroblasts or bacteria, marginal adhesion for both species occurs on coating imperfections. Because photopolymerization can easily be adapted to surface patterning, smart devices that promote both osseointegration (in non-coated areas) and prevent cell overgrowth and biofilm formation (in coated areas) demonstrate practical potential.

Finite element analysis of moisture induced thermo-mechanical delamination of semiconductor packages considering in-situ moisture desorption during reflow process

Polymers are highly affected by moisture and temperature in terms of reliability of packaging. Especially, interface delamination between dissimilar materials with polymer is one of the major issues to the structural integrity and reliability, which is affected significantly by temperature and moisture concentration. In this paper, moisture absorption characteristics and thermo-mechanical delamination of semiconductor packages were predicted by finite element analysis considering moisture and temperature changes during the reflow process simultaneously based on a home-made user's subroutine. To implement the delamination through finite element analysis, moisture absorption experiments were conducted to evaluate hygroscopic properties (diffusivity, concentration) of the package material with different relative humidities (RH) and temperatures. In addition, adhesion strength of bi-material was evaluated by a micro-scale shear test. The measured adhesion strength of bi-material such as Epoxy molding compound (EMC)/Chip, Chip/substrate, and substrate/EMC were implemented in the user's subroutine with respect to the moisture concentration and temperature. The user's subroutine based finite element analysis code was developed to analyze the combined effect of hygroscopic and thermal deformation. As a result, interface delamination was successfully predicted considering the in-situ moisture desorption and temperature increase during the reflow process and interfacial failure strength considering the temperature and moisture concentration.

A Method of Measuring Wood Failure Percentage of Wood Specimens Bonded with Melamine-Urea-Formaldehyde Resins Using Image Analysis

Transparent and colorless melamine-urea-formaldehyde (MUF) resins make it difficult to identify the area of wood failure percentage (WFP) in the fracture surface of bonded wood specimens. Therefore, in this study, we develop a method of measuring WFP after the adhesion strength measurement of MUF resins under shear stress. The fractured wood surface of block shear strength (BSS) specimens bonded with cold-setting MUF resins at three melamine contents (20%, 30%, and 40%) was marked black, and then, WFP was accurately measured via image analysis. WFP values measured using this method consistently increased with BSS as the melamine content increased, showing the reliability of this new method. The results suggested that this new method is useful and reliable for measuring the WFP of the fracture surface of wood specimens bonded with colorless adhesives such as urea-formaldehyde, MUF, and melamine-formaldehyde resins.

Adhesive Strength of Ni–Cu Surface Alloy Formation by Low-Energy High-Current Electron Beam

The paper presents the adhesive strength measurements of the Ni–Cu surface alloy formed on a copper substrate at a different thickness of the transition layer. The formation of the surface alloy is provided by the low-energy high-current electron beam of a microsecond duration; the different thickness of the transition layer is varied by the thickness of the nickel film sputtered. The multiple deposition-irradiation process is performed during one vacuum cycle. It is found that the cross-section of the film (Ni)-substrate (Cu) interface is rather developed and curved. The transition layer thickness reduces with increasing thickness of the deposited nickel film. Scratch testing shows that the adhesive strength of the Ni–Cu surface alloy obtained by using the low-energy high-current electron beam, is higher than that of the sputter-deposited surface alloy. The highest adhesion is observed for the Ni–Cu surface alloy obtained by the nickel film deposition 0.125 μm thick. In this case, the crack formation and localized film delamination occur under the critical loads of 15 and 17 N, respectively. Nevertheless, a complete delamination of the surface alloy is not observed.

Optimum Surface Roughness for Titanium-Coated PEEK Produced by Electron Beam PVD for Orthopedic Applications

ABSTRACT In this study, three different surfaces of Titanium-coated PEEK were compared by their coating strength, cell adhesion, and cell growth, which were produced through electron beam PVD. For this purpose, different samples with smooth, moderate, and coarse roughness surface were prepared. Surface roughness measurement, AFM, SEM, and EDS analyses were applied to compare surface topography, observe the thickness and roughness of the coated surface, and characterised coated materials, respectively. Also, cross-cut, in vitro and in vivo tests were performed to measure adhesion strength and biological differences between samples to validate data on the optimum sample. The results showed that the adhesion strength between the coated layer and the substrate for every sample was reliable, but Cell adhesion for the sample with moderate roughness was the best among all. Therefore, moderate surface roughness was found to be optimum due to the obtained results from the interaction between implant surface and cells.

Hydrophobic and Hydrophilic Effects in a Mussel-Inspired Citrate-Based Adhesive.

The citrate-based tissue adhesive, synthesized by citric acid, diol, and dopamine, is a kind of mussel-inspired adhesive. The adhesion of mussel-inspired adhesive is not completely dependent on 3, 4-dihydroxyphenylalanine (Dopa) groups. The backbone structure of the adhesive also greatly affects the adhesion. In this study, to explore the effects of hydrophobicity and hydrophilicity of the backbone structure on adhesion, we prepared a series of citrate-based tissue adhesives (POEC-d) by changing the molar ratio of two diols, 1, 8-octanediol (O) and poly(ethylene oxide) (E), which formed hydrophobic segment units and hydrophilic segment units, respectively, in the molecule structure. The properties of cured adhesives showed that the adhesive with high E units had high swelling, rapid degradation, and low cohesion. In the adhesion strength measurement on the porcine skin, the adhesive with higher hydrophobicity was more likely to perform better. For the interfacial adhesion, hydrophilicity was conducive to the diffusion and penetration on the skin surface, but hydrophobic interaction showed a stronger effect to adhere with skin and hydrophobic association increased the adhesive concentration on the interface; for the bulk cohesion, hydrophobicity led to coacervation, promoting the Dopa-quinone coupling for cross-linking. In this amphipathic, citrate-based, soft-tissue adhesive system, when the feed ratio of hydrophilic segment was lower than 0.7, the coacervation could be formed through hydrophobic interaction, forming an efficient underwater adhesion system similar to that of mussels.

Assessment of the Constancy of Performance of Cementitious Adhesives for Ceramic Tiles: Analysis of the Test Results Commissioned by Polish Market Surveillance Authorities

Assessment and verification of constancy of performance (AVCP) is a complex process. Without it, the manufacturer cannot mark the product with the Conformitè Europëenne (CE) marking and place it on the EU market. The verification of the correctness of the AVCP is carried out by market surveillance. In Poland, supervision authorities regularly check manufacturers by collecting construction products that exist on the market for inspection. Among the dry-mix mortars, adhesives for ceramic tiles (CTA) constitute an essential group. The requirements for CTAs are specified in EN 12004. According to the standard, the basic characteristics of cementitious CTAs are tensile adhesion strength and open time. The adhesion measurements are performed after various laboratory conditions tests. The study analyzes the results obtained for 129 samples of cementitious CTAs, collected between the years 2016 and 2019 from the market, and tested in notified laboratories at the request of Polish construction supervision authorities. Many tested products did not meet the threshold values, which resulted in removing them from the market. The paper discusses the complexity of the tensile adhesion strength measurement. The obtained test results are considered in various dimensions, including using the simple acceptance rule method when evaluating the results, which does not consider the measurement uncertainty.

Star-shaped polycaprolactone bearing mussel-inspired catechol end-groups as a promising bio-adhesive

The catechol groups in mussel adhesive proteins exhibit excellent adhesion property to the skin and tissue surfaces. Inspired by catechol groups, the aim of this study is to synthesize the star-shaped polycaprolactone bio-adhesive bearing catechol end-groups (s-PCL19-CA9). Firstly, star-shaped polycaprolactone was synthesized through ring-opening polymerization of caprolactone monomers initiated by β-cyclodextrin, and then the s-PCL19-CA9 was obtained through end-group functionalization using succinic anhydride and dopamine. The structure of s-PCL19-CA9 was characterized by 1H NMR, FTIR, and static light scattering. Adhesive strength measurements demonstrate that the incorporation of multifunctional catechol groups endows the crosslinked s-PCL19-CA9 with an excellent adhesion property (102 ± 10 kPa). The swelling ratio of crosslinked s-PCL19-CA9 is as low as 3.4 ± 0.2% owing to the hydrophobicity of PCL and the crosslinking structures. Besides, the cytotoxicity studies show that s-PCL19-CA9 is noncytotoxic. The TGA measurements indicate that s-PCL19-CA9 possesses a good thermal stability. Therefore, this work provides a new way for developing multifunctional bio-adhesives with excellent adhesion property and low swelling ratio.

Microfluidic channel for measurement of cell adhesion strength using ultrasonic

Microfluidic channel for measurement of cell adhesion strength using ultrasonic

Water and Ice Adhesion to Solid Surfaces: Common and Specific, the Impact of Temperature and Surface Wettability

Ice adhesion plays a crucial role in the performance of materials under outdoor conditions, where the mitigation of snow and ice accumulation or spontaneous shedding of solid water precipitations are highly desirable. In this brief review we compare the adhesion of water and ice to different surfaces and consider the mechanisms of ice adhesion to solids basing on the surface forces analysis. The role of a premelted or quasi-liquid layer (QLL) in the ice adhesion is discussed with the emphasis on superhydrophobic surfaces, and the temperature dependence of ice adhesion strength is considered with an account of QLL. We also very briefly mention some recent methods for the measurement of ice adhesion strength to the icephobic engineering materials outlining the problems which remain to be experimentally solved.

Strength and toughness of adhesion of soft materials measured in lap shear

Adhesion of soft materials is commonly characterized by strength and toughness. Their applicability, however, is often questionable even for widely used test methods. Here we study lap shear using a combination of experiment, theory, and computation. Lap shear has long been used to measure adhesion strength of soft materials, but our experiments show that the measured adhesion strength is constant only when the sample is thin and short enough. When the sample thickness exceeds the fractoadhesive length, the corner of the sample concentrates stress, and the adhesion strength decreases as the sample thickness increases. When the sample length exceeds the shear lag length, the backing layer deforms appreciably, much of the sample does not carry shear stress, and the adhesion strength decreases as the sample length increases. Furthermore, we derive an analytical expression for energy release rate for a crack long compared to the sample thickness. For samples thicker than the fractoadhesive length, we show that the adhesion toughness is constant, independent of the sample length. These findings will guide the development of the methods to characterize strength and toughness of adhesion.

Environmental barrier coatings using low pressure plasma spray process

AbstractYb2Si2O7/Si bilayer environmental barrier coatings (EBCs) on SiC ceramic substrate were produced by low pressure plasma spray (LPPS) process. Phase composition, microstructure, and thermal durability of LPPS Yb2Si2O7/Si coating were investigated. XRD analysis indicated that the coating is mainly composed of Yb2Si2O7 with ~15.5v% Yb2SiO5 phases. The LPPS EBCs have a dense microstructure with porosity less than 4%. Adhesion strength measurement indicated the LPPS EBCs have an average adhesion strength of 29.1 ± 0.8 MPa. Furnace cycle test (FCT) on the coatings in air at 1316°C was performed and the test ran for 900 cycles and there was no coating spallation/failure for LPPS Yb2Si2O7/Si EBCs. The FCT results demonstrated the excellent thermal cycle durability of LPPS EBCs. Oxidation kinetics investigation of LPPS EBCs in flowing 90% H2O (g)+10% air at 1316°C showed that the thermally grown oxide (TGO) growth rate is close to the oxidation rate of pure Si in dry air and is significantly lower than that in water vapor environment. The LPPS process is promising in making highly durable Yb2Si2O7‐based dense EBCs by impeding diffusion and ingression of water vapor/O2.

Use of loading devices with low stiffness may cause uncertainty in measuring the strength of cellular adhesion

ABSTRACT Cellular adhesion via the formation of molecular bond clusters is a fundamental biological phenomenon. Cell adhesion forces can be measured by various advanced techniques with adjustable probe stiffness. To quantitatively understand how the stiffness of a loading device may influence the measurement of these forces, we consider an idealized theoretical model of a cluster of molecular bonds that are subjected to an applied tensile load by a Hookean spring. In this model, the rebinding and rupture of individual molecular bonds are governed by stochastic master equations. By deriving an exact expression of the rebinding rate and directly solving the master equation, we find that the conventional moment method provides incorrect predictions for this problem. Moreover, the measured adhesion strength of a molecular bond cluster exhibits strong dependence on the stiffness of the loading device and the bond number when the stiffness value is close to or smaller than the effective stiffness of the bond cluster. Thus, an improper selection of the stiffness value of the loading device may lead to measurement uncertainty. Monte Carlo simulations are performed to verify the proposed analytical results.

The differential role of CR3 (CD11b/CD18) and CR4 (CD11c/CD18) in the adherence, migration and podosome formation of human macrophages and dendritic cells under inflammatory conditions.

CR3 and CR4, the leukocyte specific β2-integrins, involved in cellular adherence, migration and phagocytosis, are often assumed to have similar functions. Previously however, we proved that under physiological conditions CR4 is dominant in the adhesion to fibrinogen of human monocyte-derived macrophages (MDMs) and dendritic cells (MDDCs). Here, using inflammatory conditions, we provide further evidence that the expression and function of CR3 and CR4 are not identical in these cell types. We found that LPS treatment changes their expression differently on MDMs and MDDCs, suggesting a cell type specific regulation. Using mAb24, specific for the high affinity conformation of CD18, we proved that the activation and recycling of β2-integrins is significantly enhanced upon LPS treatment. Adherence to fibrinogen was assessed by two fundamentally different approaches: a classical adhesion assay and a computer-controlled micropipette, capable of measuring adhesion strength. While both receptors participated in adhesion, we demonstrated that CR4 exerts a dominant role in the strong attachment of MDDCs. Studying the formation of podosomes we found that MDMs retain podosome formation after LPS activation, whereas MDDCs lose this ability, resulting in a significantly reduced adhesion force and an altered cellular distribution of CR3 and CR4. Our results suggest that inflammatory conditions reshape differentially the expression and role of CR3 and CR4 in macrophages and dendritic cells.

Titanium dioxide nanoparticles reinforced experimental resin composite for orthodontic bonding

The aim of this laboratory study was to evaluate the effect of titanium dioxide (TiO2) nanoparticles reinforced experimental adhesive resin for orthodontic bonding. The experimental resin (bis-Phenol-A free) was prepared using urethane dimethacrylate, hydroxypropyl methacrylate, camphorquinone and N, N-cyanoethyl methylaniline. TiO2 nanoparticles were added at 1 weight-% and 3 weight-% of the experimental resin composite and were labeled as RC1 (1 weight-% TiO2) and RC3 (3 weight-% TiO2), and non-reinforced resin composite was used as control (RC). A total of 90 extracted human premolars were randomly assigned into 3 groups. In group RC, metal orthodontic brackets were bonded to the enamel surface using experimental resin (without TiO2). In the group RC1, the brackets were bonded using resin RC1, and in the group RC3, the brackets were bonded using resin RC3. Fifteen randomly selected specimens from each study group were subjected to artificial aging, and the remaining fifteen served for the baseline adhesion strength measurements. Adhesion strength was measured and recorded using a universal testing machine. Fluidity and anti-bacterial activity of the experimental and reinforced resins were determined. The highest adhesion strength at baseline was seen in group RC1 (13.2 ± 1.8 MPa), and the lowest values was seen in the group RC (12.5 ± 1.8 MPa). Following thermo-cycling, the highest adhesion strength was observed in the group RC1 (12.4 ± 2.4 MPa) and the lowest values were seen in the group RC (10.6 ± 1.6 MPa). A significant difference (ANOVA) was observed between the groups (both baseline and thermo-cycled groups) except for group RC1 (p > 0.05). The resin in the RC group demonstrated more fluidity compared to the experimental groups. Among the experimental groups, group RC3 demonstrated less fluidity compared to group RC1. The colony forming units (CFUs) were high in group RC and the least values were found in group RC1. Addition of 1% TiO2 to the BPA and bis-GMA free experimental resin demonstrated promising flow and anti-bacterial effect without compromising the adhesion strength or chemical properties.

Experimental evaluation of interfacial adhesion strength of cold sprayed Ti-6Al-4V thick coatings using an adhesive-free test method

Cold spray (CS) is a rapidly growing solid-state additive material deposition technique often used for repair of high-value metallic components. This study aims at evaluating the interfacial adhesion strength of cold sprayed Ti-6Al-4V (Ti-64) coatings deposited onto Ti-64 substrates for repair applications. An adhesive-free test method, referred as modified Collar-Pin Pull-off Test was developed based on Sharivker's (1967) original design, in order to overcome the limitations of existing test approaches (both adhesive-based and adhesive-free). This method was designed to allow measurement of adhesion strength of high strength coatings such as CS Ti-64, where adhesion strength is higher than 70–90 MPa. A parametric study was performed to assess the effect of coating thickness, scanning speed, track spacing, toolpath pattern, and substrate surface preparation on the coating adhesion strength. A finite element model was also used to evaluate the stress distribution during the pull-off test, and to check the validity of the proposed test method. The proposed adhesive-free test method was found to be capable of measuring coatings with adhesion strengths beyond the upper limit of conventional adhesive-based methods such as ASTM C633. Among the investigated cases, the highest value of coating adhesion strength was measured around 122 MPa, in the case of CS Ti-64 deposited on ground Ti-64 substrates.