Adhesive and Rheological Properties of Lightly Crosslinked Model Acrylic Networks

The viscoelastic and adhesive properties of a series of model, lightly crosslinked acrylic polymer networks have been investigated. The model networks were statistical copolymers of 2-ethyl-hexyl acrylate and acrylic acid or terpolymers of 2-ethyl-hexyl acrylate, acrylic acid, and stearyl acrylate synthesized in solution. All were lightly crosslinked after the polymerization was completed to obtain typical properties of pressure-sensitive adhesives. The bulk rheological properties of the networks were characterized by dynamical mechanical spectroscopy and in uniaxial extension. Their adhesive properties were tested with an instrumented probe tester fitted with a cylindrical steel probe. The presence of acrylic acid in the copolymer caused an increase in both elastic modulus and resistance to interfacial crack propagation characterized by the critical energy-release rate G_c and the incorporation of stearyl acrylate caused a decrease in both modulus and G_c. In both cases, however, the modification of G_c controlled the overall behavior. The analysis of the nonlinear elastic properties of the adhesives with the Mooney-Rivlin model provided new insights on the role played by the ratio between entanglements and crosslink points in controlling the formation and extension of the bridging fibrils observed upon debonding.     

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.     

硅橡胶与玻璃布的粘接研究

研究了旨在提高橡胶／玻璃布拉粘接性能的玻璃布的表面处理，并地影响其粘接强度的因素进行了讨论。结果表明，ＫＨ５５０／Ａ１５１、间苯二酚／Ａ１５１是其处理的有效体系。     

MEASURING INTERFACIAL ADHESION BETWEEN A SOFT VISCOELASTIC LAYER AND A RIGID SURFACE USING A PROBE METHOD

A reliable measure of the adhesion between a very deformable material and a solid surface is rather difficult, since the interface boundary conditions and the bulk deformation of the layer are closely and very nonlinearly coupled. In this article, a new methodology to assess the adhesion of a soft viscoelastic layer on a solid surface is proposed, where we have used a specific experimental geometry minimizing the bulk deformation of the layer. A flat-ended probe is first put in contact with a thin layer of soft material and removed at a constant velocity. The probe is then stopped at a preset level of tensile force and the time for complete debonding of the layer from the probe is measured. For our model system, comprised of a soft acrylic removable adhesive and a silicone-coated surface, the higher the applied force the faster the interfacial fracture occurs, leading to an experimental curve of the adhesion energy as a function of average crack velocity. We find that the methodology is relatively simple to implement and should be widely applicable for weakly adhering soft layers of arbitrary viscoelastic properties. The assumptions involved in such an analysis and their inherent limitations are also illustrated experimentally and critically discussed.     

MEASURING INTERFACIAL ADHESION BETWEEN A SOFT VISCOELASTIC LAYER AND A RIGID SURFACE USING A PROBE METHOD

A reliable measure of the adhesion between a very deformable material and a solid surface is rather difficult, since the interface boundary conditions and the bulk deformation of the layer are closely and very nonlinearly coupled. In this article, a new methodology to assess the adhesion of a soft viscoelastic layer on a solid surface is proposed, where we have used a specific experimental geometry minimizing the bulk deformation of the layer. A flat-ended probe is first put in contact with a thin layer of soft material and removed at a constant velocity. The probe is then stopped at a preset level of tensile force and the time for complete debonding of the layer from the probe is measured. For our model system, comprised of a soft acrylic removable adhesive and a silicone-coated surface, the higher the applied force the faster the interfacial fracture occurs, leading to an experimental curve of the adhesion energy as a function of average crack velocity. We find that the methodology is relatively simple to implement and should be widely applicable for weakly adhering soft layers of arbitrary viscoelastic properties. The assumptions involved in such an analysis and their inherent limitations are also illustrated experimentally and critically discussed.     

Effect of a Gradient in Viscoelastic Properties on the Debonding Mechanisms of Soft Adhesives

The effect of a composition gradient along the thickness in soft adhesive films was investigated. The adhesion properties of bilayer films made from acrylic solutions, one layer being more cohesive and the other more dissipative, were studied by performing probe tack experiments. To understand the mechanisms that determine the bulk and the interfacial contributions to the debonding, tests on different surfaces were carried out. The results show that the presence of a composition gradient can enhance the adhesive properties, particularly on a low-energy surface such as polyethylene. On steel, the presence of the thin layer of a more elastic adhesive in contact with the adherent can influence significantly the debonding mechanism, transforming the fracture from cohesive to adhesive.     

Effect of a Gradient in Viscoelastic Properties on the Debonding Mechanisms of Soft Adhesives

The effect of a composition gradient along the thickness in soft adhesive films was investigated. The adhesion properties of bilayer films made from acrylic solutions, one layer being more cohesive and the other more dissipative, were studied by performing probe tack experiments. To understand the mechanisms that determine the bulk and the interfacial contributions to the debonding, tests on different surfaces were carried out. The results show that the presence of a composition gradient can enhance the adhesive properties, particularly on a low-energy surface such as polyethylene. On steel, the presence of the thin layer of a more elastic adhesive in contact with the adherent can influence significantly the debonding mechanism, transforming the fracture from cohesive to adhesive.     

Adhesion of Patterned Reactive Interfaces

We demonstrate the role of chemical surface patterns on the adhesion of soft, elastomeric interfaces. The microscale patterns consist of periodic variation of two types of silane surface chemistries: a reactive silane that bonds covalently with the soft elastomer and a passive silane that is weakly adhered with the elastomer. Using an adhesion test based on 90° peel geometry, we demonstrate that the tuning of adhesion depends on the spatial distribution of the reactive silane groups. Given our material system and pattern symmetries, an enhancement in adhesion energy is observed in a majority of the patterns. The mechanism of enhancement is associated with the shape of the contact line. Specifically, the reactive silane interfaces play a significant role in defining the width of the contact line. In instances where enhancement is observed, the width of the contact line increases because of the “pinning” of the contact line by the reactive interfaces. These results emphasize the importance of contact line interaction with the pattern shapes and demonstrate opportunities for using well-defined two-dimensional patterns to actively tune polymer adhesion.     

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     

Atmospheric Pressure Plasma Polymerised Primer to Promote Adhesion of Silicones

By combining a liquid primer and a plasma jet system, a new route to improved adhesion on various substrates has been developed. The liquid primer is introduced as an aerosol into a plasma jet and the resultant active species are deposited as a polymer coating on adjacent surfaces. Careful control of the plasma parameters produced a dry polymerised coating with functional chemistry designed to enhance the adhesion of silicone sealants to two substrates. This paper describes the surface chemistry and adhesion properties of various coatings on both a plastic and a metal substrate. Selected surface analysis techniques were coupled to both wet and dry adhesion testing to characterise the factors that control adhesion within the system. Mechanical testing indicates that adhesion was improved by several orders of magnitude.     

甲基MQ及MTQ型硅酮树脂的合成及其特性

研究了以偏硅酸钠、六甲基二硅氧烷为基本原料合成甲基ＭＱ及ＭＴＱ型硅酮树脂的方法,内容包括水解反应温度的影响,投料比例的影响,反应时间的影响,交链剂对ＭＴＱ型树脂性能的影响以及ＭＱ及ＭＴＱ树脂与液体硅橡胶配伍作为胶粘剂的粘接性能的研究等。     

Adhesion of a liquid-filled spherical membrane

Solid/solid interfacial interactions have been successfully characterised using the Johnson, Kendall, and Roberts (JKR) analysis for many years now. Following a suggestion and accompanying analysis by the present author to replace a solid sphere by a gas-filled, hollow, spherical membrane in contact experiments, we now propose a liquid-filled "balloon." Free energy changes due to stretching, bending, the mechanical contact force and adhesion are assessed and minimised to obtain an exploitable equation permitting estimation of the energy of adhesion of the system as a function of various, in principle more easily measured, parameters.     

Adhesion of Wax Droplets to Porous Polymer Surfaces

An experimental study was done to measure the force of adhesion of molten wax droplets, 3.1 mm in diameter, dropped from heights ranging from 20 to 50 mm onto porous polyethylene and Teflon surfaces. The Teflon surface had 0.25-mm holes drilled in it and the three polyethylene surfaces had random pores with mean diameters of 35, 70, and 125 μm, respectively. The force required to remove the solidified ink from the surface was measured using a pull test. Wax splats were attached to the substrate by both adhesive and cohesive forces. The cohesive force was calculated by multiplying the ultimate tensile strength of the wax (2.2 MPa) by the cross-sectional area of the wax penetrating into surface pores. The adhesive force was obtained by multiplying the contact area between the wax and substrate by the adhesion strength per unit area, estimated to be 0.2 MPa for polyethylene and 0.1 MPa for Teflon surfaces. The contact area between splats and the substrate was typically about 60–70% of the splat area. The edges of splats lifted up, preventing complete contact.     

Modulation of Adhesion at Acrylic Adhesive-Silicone Elastomer Interfaces

We have recently reported a systematic investigation of the role of MQ resins (small silica-like nanoparticles) in the modulation of adhesion at silicone elastomer lens—nanometric thin acrylic surface anchored layer deposited on a silicon wafer through loading and unloading JKR experiments. This particular system was chosen as it allowed one to vary the MQ resin content in the elastomer, and to test its resulting effect on both the thermodynamic work of adhesion and the adhesive strength at elastomer—acrylic layer interfaces, avoiding any complication due to bulk mechanical properties of a relatively thick (in the micron range) acrylic layer. We present here a complementary investigation, aimed at understanding the role of the resins in the development of specific interactions at the interface. To do so the adhesive energy between silicone elastomers containing various amounts of MQ resins and model substrates made of self-assemble monolayers of thiol molecules with various amounts of carboxylic terminations have been measured through JKR tests. We show that the level adhesion at these interfaces results from a competition between increased interactions and decreased mobility associated with the incorporation of the resins inside the elastomer.     

Modulation of Adhesion at Silicone Elastomer-Acrylic Adhesive Interface

To characterize the role of small silica like nanoparticles (MQ resins) in the modulation of adhesion at polydimethyl siloxane (PDMS) elastomers-acrylic adhesive contacts, we have designed systems in which the roles of MQ resins in enhancing interactions at the interface and in increasing viscoelastic dissipations in the elastomer layer could be separated. First, the contact between elastomers with various MQ resin contents and PDMS layers made of densely grafted short chains has been investigated through Johnson-kendall-Roberts (JKR) tests, in order to characterize how the dissipations in the elastomer depend on the resin content. The same elastomers in contact with thin-surface-anchored acrylic layers were then tested through JKR tests to determine the role of enhanced interactions in the modulation of adhesion at the interface due to the resins. In these experiments, the thickness of the acrylic layer was kept small enough so that dissipations in the acrylic adhesive could be neglected. Both G₀, the adhesive strength at zero fracture velocity, and G( V), the velocity-dependent fracture toughness, strongly depend on the MQ resin content and on the contact time, suggesting the progressive building of strong interactions between acrylic and elastomer chains.     

Modulation of Adhesion at Acrylic Adhesive-Silicone Elastomer Interfaces

We have recently reported a systematic investigation of the role of MQ resins (small silica-like nanoparticles) in the modulation of adhesion at silicone elastomer lens—nanometric thin acrylic surface anchored layer deposited on a silicon wafer through loading and unloading JKR experiments. This particular system was chosen as it allowed one to vary the MQ resin content in the elastomer, and to test its resulting effect on both the thermodynamic work of adhesion and the adhesive strength at elastomer—acrylic layer interfaces, avoiding any complication due to bulk mechanical properties of a relatively thick (in the micron range) acrylic layer. We present here a complementary investigation, aimed at understanding the role of the resins in the development of specific interactions at the interface. To do so the adhesive energy between silicone elastomers containing various amounts of MQ resins and model substrates made of self-assemble monolayers of thiol molecules with various amounts of carboxylic terminations have been measured through JKR tests. We show that the level adhesion at these interfaces results from a competition between increased interactions and decreased mobility associated with the incorporation of the resins inside the elastomer.     

化学微交联聚氯乙烯的结构和性能

通过氯乙烯/邻苯二甲酸二烯丙酯(VC/DAP)悬浮共聚,合成了含部分凝胶结构的化学微交联PVC树脂,对微交联PVC的玻璃化转变行为、加工性能、消光性能、加热-形变行为和力学性能进行了研究。当DAP用量在0.25%mol以下时,PVC的玻璃化温度变动不大。凝胶含量的增加将导致交联PVC_d~T的光泽度下降,消光性能提高;塑化时间和加工扭矩均增加,加工性能急剧变差;加热变形值下降,最高使用温度提高。凝胶对PVC拉伸性能的影响较为复杂,但压缩永久变形则随凝胶含量的增加而下降,材料的弹性性能逐渐提高。     

Effect of Blend Ratio on Adhesion Properties of Pressure-Sensitive Adhesives Prepared from SBR/SMR L Blends

The viscosity, tack, and peel strength of an SBR/SMR L-based pressure-sensitive adhesive was studied. Coumarone–indene resin and toluene were used as the tackifier and solvent, respectively, throughout the experiment. The blend ratio of SBR/SMR L was varied from 0 to 100% whereas the resin content was increased from 40 to 120 parts per hundred parts of rubber in the adhesive formulation. The viscosity was determined by a HAAKE rotary viscometer. Loop tack and peel strength of paper/polyethylene terephthalate film were measured using a Lloyd adhesion tester operating at 30 cm/min. Results show that the viscosity of the adhesive decreases with % SBR but increases with resin loading. Loop tack of adhesive indicates a maximum value at 20% SBR for all resin loadings. The peel strength, however, exhibits maximum value at 40% SBR for the three modes of peel tests, an observation which is attributed to the optimum wettability of adhesive on the substrate where formation of mechanical interlocking and anchorage of the adhesive in pores and irregularities in the substrate occurs.     

The Mechanical Properties of Polymer Glasses

Polymer glasses are widely used in the container, appliance, construction, aerospace, and automobile industries in the form of compression or injection molded parts, solvent cast films, extruded films, coatings, adhesives, and composites. The increasing use of polymeric glasses in extreme service environments, particularly in the aerospace industry, requires a knowledge of their lifetime in such environments. To predict the lifetime of polymeric glasses in a service environment requires knowledge of: (1) details of the particular environment, (2) the nature of the failure processes, (3) the effect of the failure processes on the mechanical properties, (4) the structural parameters affecting the failure processes, and (5) how these structural parameters are modified by fabrication procedures and the service environment.