Soft and Hard Adhesion

The force needed to pull a cylindrical stud from a soft elastomeric film depends on their elastic and geometric properties. For a rigid stud and a thick elastomeric film, the pull-off stress (σ) depends on the elastic modulus (E) of the film and the radius (a) of the stud as σ ∼ (E/a)^1/2 (soft adhesion). However, when the film is very thin, the pull-off stress is significantly higher than the case with thick films, and its value depends on the elastic modulus and the thickness (h) of the film as σ ∼ (E/h)^1/2 (hard adhesion). Here, we study the pull-off behavior of a soft cylindrical stud, one flat end of which is coated with a high modulus thin baseplate. As the flexural rigidity of this baseplate is varied, we observe the transition between the two types of adhesion. We present a simple physical interpretation of the problem, which could be of value in understanding various biofouling and adhesive situations.     

Soft and Hard Adhesion

The force needed to pull a cylindrical stud from a soft elastomeric film depends on their elastic and geometric properties. For a rigid stud and a thick elastomeric film, the pull-off stress (σ) depends on the elastic modulus (E) of the film and the radius (a) of the stud as σ ～ (E/a)^1/2 (soft adhesion). However, when the film is very thin, the pull-off stress is significantly higher than the case with thick films, and its value depends on the elastic modulus and the thickness (h) of the film as σ ～ (E/h)^1/2 (hard adhesion). Here, we study the pull-off behavior of a soft cylindrical stud, one flat end of which is coated with a high modulus thin baseplate. As the flexural rigidity of this baseplate is varied, we observe the transition between the two types of adhesion. We present a simple physical interpretation of the problem, which could be of value in understanding various biofouling and adhesive situations.     

HMX塑料粘结炸药的粘接研究

测试了水和甲酰胺对 HMX塑料粘结炸药 (PBX)药柱表面的接触角 ,它们的接触角分别为 82°和 32°;计算了 HMX药柱的表面能为 91 m N/ m,这表明 HMX塑料粘结药柱表面为低能表面。比较了几种结构胶粘剂粘接药柱的剪切强度 ,使用环氧胶时为 7.6MPa。试验发现胶粘剂种类、厚度对 HMX塑料粘结剂药柱爆速的影响较小     

Internal stress and wet adhesion of organic coatings

Internal stress in organic coatings has been considered for a long time as the origin of cracking and checking. However, much more interesting and informative are changes of internal stress when coatings are exposed to water. It is demonstrated that these changes indicate interfacial relaxation processes at the coating/support interface, which are related to wet adhesion and to the recovery of adhesion after the evaporation of water and allow the measurement of the permeability of coatings on substrates to water. There is evidence that a special state of adhesion exists before delamination takes place, which may be characterized as ‘sliding or mobile bonding’.     

Studies on Adhesion Between Natural Rubber and Polyethylene and the Role of Adhesion Promoters

Studies on adhesion between natural rubber (NR) and polyethylene (PE) with different levels of interaction (physical and chemical) have been carried out. Ethylene propylene diene rubber (EPDM) and chlorinated polyethylene (CPE) were used as physical promoters and epoxidised natural rubber/modified polyethylene (ENR/PEm) and sulfonated ethylene propylene diene rubber/modified polyethylene (S-EPDM/PEm) were used as chemical adhesion promoters. The failure surfaces were examined with the help of scanning electron microscopy (SEM), optical photography and electron spectroscopy for chemical analysis (ESCA) techniques.

The peel strength between natural rubber and polyethylene as measured in this study is 140 J/m². With the incorporation of physical promoters such as EPDM, the peel strength increases twenty fold because of structural similarity of EPDM with PE and the rubbery nature of EPDM. Similarly, the other promoters show significant improvement in peel strength. At high temperature and low rate of peeling, the nature of failure is mainly “stick-slip” for joints with interaction promoters. The average peel strength increases with increase in test rate and decrease in test temperature for most of the joints. All the data could be shifted onto a master curve indicating that the increase in strength is a result of viscoelastic dissipation. NR/EPDM/PE and NR/CPE/PE systems, however, behave in a different way probably because they alter the nature of crack propagation at or near the interface. ESCA results of the peeled PE surface show a chemical shift of C_1S peak. SEM photographs also indicate interaction at the interface when modifiers are used. An increase in crystallinity of PE from 30% to 64% and modulus increase the peel strength of NR/PE joints by a factor of four. The results of peel strength measurement at 90° are lower than those at 180°. Lap shear results are in line with peel strength.     

Molecular Studies of Adhesion and De-Adhesion on ZnO Nanorod Film-Covered Metals

This paper aims at the investigation of the effect of ZnO nanorod film deposition on the adhesion between a zinc surface and a model epoxy-based adhesive, with and without the adhesion promoter 3-aminopropylphosphonic acid (APPA) treatment. The stability of octadecylphosphonic acid (ODPA) monolayers on ZnO nanorod surfaces was investigated by means of contact angle measurements and FT-IRRAS to simulate wet de-adhesion conditions at the phosphonate-zinc oxide interface. Peel tests were performed under controlled humidity to study the wet de-adhesion of the model epoxy-amine coating from the ZnO nanorod surface. The deposition of ZnO nanorod films resulted in a significant increase of peel forces in comparison with bare zinc. In the case of APPA-treated ZnO nanorod films the increase of the macroscopic adhesion forces was more pronounced. The high surface area ZnO nanorod films provide for the adsorption of polymers as well as adhesion promoters and makes them promising candidates for improving the adhesion properties of engineering metals.     

Thermodynamic Criteria for the Maximum and Minimum Strength of Fibre-Reinforced Composite Materials

The overall performance and reliability of composite materials are, in most cases, dependent upon the behaviour of the reinforcement-matrix interface, particularly upon its ability to transfer stress.

A theory for predicting thermodynamic conditions for the maximum and zero-adhesion at the reinforcement-matrix interface is tested in this paper, based on experimental data. Proposed is a model of the relationship between mechanical properties of composite materials (tensile strength, flexural strength, Young's modulus and impact resistance) and energetic properties of matrix and reinforcement expressed by the energy ratio a = γ_l/γ₂.     

Adhesion between polyurethane coating and EPDM rubber compound

The effect of the bulk modification of the EPDM rubber compound on the adhesion performance with polyurethane coating (PU) was studied. Ethylene propylene diene monomer (EPDM) was bulk modified using maleated EPDM, polynorbornene (PNR) or different curatives to improve adhesion to polyurethane coating. The coating–rubber composite adhesion performance was examined by peel, crack and abrasion tests followed by microscopic investigation of fracture surfaces and their chemical nature. The adhesion between the coating and the rubber substrate was improved using maleated EPDM or PNR, as well as different curing systems. The crack stress for the delamination of the polyurethane coating from the flexible bulk-modified rubber surface follows the trend: maleated EPDM > PNR > different curing systems > control.     

Adhesion of Polypropylene Fiber to Cement Matrix

Abstract

In this research, the adhesion of polypropylene (PP) fibers to cementitious matrix has been investigated and the chemical bonding and mechanical interlocking between PP fiber and hardened cement paste has been studied. Furthermore, thermodynamic work of adhesion and loss-function (dissipation energy) has been calculated in the PP-cement matrix model system. To investigate the work of adhesion, the pull-out test has been used. Also, the surface free energy and contact angle of the PP monofilaments and cement matrix have been measured using a tensiometer and the fiber–cement interfacial interactions and thermodynamic work of adhesion and loss-function were calculated. Scanning electron microscopy (SEM) analysis was used to study the fiber–cement matrix interfacial transition zone (ITZ). The results showed that the application of theories of polymer–polymer adhesion in fiber–cement matrix systems was feasible. To verify the accuracy of the method, the adhesion of two other fibers (nylon 6,6 and acrylic polymer) was studied.     

Model Studies of the Effect of Surface Roughness and Mechanical Interlocking on Adhesion

The apparent strength of adhesion has been measured for a soft elastic layer adhering to model porous substrates, consisting of rigid plates containing regular arrays of cylindrical holes. Two contributions to the apparent strength have been identified and compared with the predictions of a simple theoretical treatment. The first is adhesion to the surface itself. Because “rough” surfaces have greater area for bonding, the strength of adhesion was increased by as much as twenty-fold. The second arises from the work of breaking deeply embedded or entangled strands in order to detach the overlayer. Contributions from this mechanism were as much as several hundred times the (low) intrinsic strength of adhesion. Satisfactory agreement was obtained with theory in both cases. Measurements were also made using cloth substrates, when the adhering layer penetrated the cloth completely. The work of detaching and breaking permeating strands was again much larger than the intrinsic strength of adhesion, in reasonable agreement with theoretical predictions.     

Relative Adhesion Measurement for Thin Film Microelectronics Structures

There is a difference between technologically-important adhesion or practical adhesion, and fundamental or basic adhesion. What is important in the understanding of fundamental adhesion may be of insignificant interest to technology. A manufacturer is interested in how to improve the reliability of the structure being built should an interface problem exist, rather than knowing the precise value of the fundamental adhesion. It is not possible to measure fundamental adhesion for technologically-important structures due to the inability to account for all energy dissipating processes during the test. Adhesion measurements are plagued with the mode of interface loading issue: the resemblance of test interface loading to that of the actual manufactured part. What technology needs is a simple adhesion test method that is practical for product development, giving reliable information about the interface integrity. The present paper compares the value of two adhesion tests for microelectronics applications and emphasizes the importance of locus of failure analyses. A realignment of structure reliability modeling is suggested by the usage of effective fundamental adhesion instead of the standard undeterminable fundamental adhesion.     

Relative Adhesion Measurement for Thin Film Microelectronics Structures

There is a difference between technologically-important adhesion or practical adhesion, and fundamental or basic adhesion. What is important in the understanding of fundamental adhesion may be of insignificant interest to technology. A manufacturer is interested in how to improve the reliability of the structure being built should an interface problem exist, rather than knowing the precise value of the fundamental adhesion. It is not possible to measure fundamental adhesion for technologically-important structures due to the inability to account for all energy dissipating processes during the test. Adhesion measurements are plagued with the mode of interface loading issue: the resemblance of test interface loading to that of the actual manufactured part. What technology needs is a simple adhesion test method that is practical for product development, giving reliable information about the interface integrity. The present paper compares the value of two adhesion tests for microelectronics applications and emphasizes the importance of locus of failure analyses. A realignment of structure reliability modeling is suggested by the usage of effective fundamental adhesion instead of the standard undeterminable fundamental adhesion.     

Improved Adhesion of Waterborne Polyurethanes by Hybridizations

Aqueous polyurethane dispersions based on isophorone diisocyanate (IPDI), poly (tetramethylene adipate) glycol (PTAd), and dimethylolproprionic acid (DMPA) were synthesized by a prepolymer mixing process. Effects of the molecular weight of PTAd and types of hybridizations, viz. blending, semi-interpenetrating polymer network (IPN), and full IPNs with polybutylacrylate have been determined. It was found that thermal, mechanical, and adhesion properties of the polyurethane dispersions increased with increasing molecular weight of polyols.

Regarding the effects of hybridization, full IPNs gave the greatest tensile strength and elongation at break with a fast drying rate, whereas semi-IPNs gave the greatest initial as well as final adhesion, implying that a certain degree of chain mobility would augment the penetrations of adhesive molecules into the soft polyurethane foam substrates.     

Adhesion Between Rubber Compounds and Copper-film-coated Steel Plates

Three copper-film-coated steel plates (abbreviated hereafter as copper-coated plate) with different thicknesses of copper film 30 to 90 nm were prepared and their adhesion properties to rubber compounds were examined. The high adhesion of copper-coated plates to the rubber compound containing resinous bonding additives was obtained at normal and over-cure conditions The copper-coated plate containing an amount of copper coating sufficient to plate the surface with a uniform copper layer showed better adhesion than that having a small amount of copper coating on its surface. The stability against green humidity aging and the cause for the high adhesion of the copper-coated plate were discussed compared with those of the brass plate.     

Adhesion Between Rubber Compounds and Copper-film-coated Steel Plates

Three copper-film-coated steel plates (abbreviated hereafter as copper-coated plate) with different thicknesses of copper film 30 to 90 nm were prepared and their adhesion properties to rubber compounds were examined. The high adhesion of copper-coated plates to the rubber compound containing resinous bonding additives was obtained at normal and over-cure conditions The copper-coated plate containing an amount of copper coating sufficient to plate the surface with a uniform copper layer showed better adhesion than that having a small amount of copper coating on its surface. The stability against green humidity aging and the cause for the high adhesion of the copper-coated plate were discussed compared with those of the brass plate.     

Adhesion Between Rubber Compound and Copper-Film-Plated Steel Cord

Four copper-film-plated steel cords (abbreviated hereafter as copper-plated cord) with different thickness of copper film from 32 to 90 nm were prepared and their adhesion properties with rubber compound were investigated. Adhesion properties improved with the decrease in the thickness of the copper film. Unaged pull-out force and rubber coverage of copper-plated cords were inferior to those of brass-plated cord, but adhesion degradation was significantly slower on copper-plated cords resulting in better adhesion after humidity aging of 15 days and salt solution aging of 5 days. The excellent adhesion stability of copper-plated cords can be explained by the suppression of the excessive growth of copper sulfide and the inhibition of dezincification due to the small amount of copper plating and the lack of metallic zinc at the outer surface.     

Effect of Surface Energetics of Substrates on Adhesion Characteristics of Poly (p-xylylenes)

In investigating the effect of the surface energetics of substrate materials on the adhesion characteristics of poly(p-xylylene) and poly(chloro-p-xylylene) by the “Scotch Tape” method, it was found that if the substrates had not been preconditioned (treated with argon or a methane plasma), the adhesion was poor. The characteristics of water resistant adhesion that were observed when coated substrates were boiled in 0.9% sodium chloride solution were found to vary from excellent (when the polymer did not peel from the substrate after three cycles of 8 hours of boiling and 16 hours at room temperature) to poor (when the polymer peeled off almost immediately). It was noticed that water resistant adhesion depends on the hydrophobicity of the substrate material (the greater the hydrophobicity, the greater the adhesion) and is not related to the dry adhesive strength of poly(p-xylylene). The oxygen glow discharge treatment of the substrates decreased both the dry and wet adhesive strength of the polymer. The effect of the argon glow discharge treatment depended on the surface energetics of the substrate, and the methane glow discharge treatment increased both the dry and wet adhesive strength of the polymer. These preconditioning processes are discussed in terms of the sputtering of the material from the wall of the reactor in contact with the plasma and the deposition of the plasma polymer of the sputtered material on the substrate surface.     

Adhesion modification of polyolefin surfaces with sodium hypochlorite in acidic media

Increased surface adhesiveness of HDPE is achieved by immersing it in an aqueous solution of sodium hypochlorite (bleach) mixed with an acid. This process results in the addition of functionality to the polymer surface vastly altering its adhesive, polarity and surface reactivity. Analysis of the modified polymer surfaces by ESCA has shown that chlorine atoms have been added to the surface. Studies regarding the chlorination of small molecules have also shown that the chlorination process is amenable to a variety of chlorination objectives and offers a route toward the functionalization of a variety of polymeric and non-polymeric substrates. In particular, this treatment renders unpaintable substrates such as HDPE more receptive to application of paints and adhesives. In this paper, we report the results of paint adhesion studies on treated polymer surfaces.     

环氧粉末涂层对金属基材附着力的影响因素

环氧粉末涂料具有附着力好、耐腐蚀性强、耐温性能好等优点,在金属防腐特别是重防腐领域应用非常广泛。在环氧粉末涂层的诸多性能中,涂层对基材的附着力是非常重要的一项技术指标,也是满足其他性能的基础,附着力的好坏直接影响着涂层对基材的保护寿命。本文主要从喷涂温度、基材表面处理的表面粗糙度以及粉末涂料原材料等方面讨论了环氧涂层对金属基材表面附着力的影响因素。研究表明:喷涂温度提高有利于涂层附着力的提高,表面粗糙度提高且锚纹深度相对均匀有利于涂层附着力的提高,填料以及助剂的种类对附着力具有一定的影响。