Effect of interfacial slippage in peel test: Theoretical model

Peel test is an efficient method to assess the performance and characteristics of materials such as adhesives and adhesive tapes. Recent experiments evidenced that the measured adhesive strength is closely related to the shear-induced interfacial slippage near the delamination front due to the concomitant Poisson contraction effect of the adhesive. Based on the experimental observations, a theoretical model is presented in this paper to examine the effect of the shear-induced interfacial slippage in the peel test. The influence of the interfacial slippage, represented by the shear displacement in the cohesive zone, on the fracture energy of decohesive zone is analyzed. An implicit expansion method with a Gauss-Chebyshev quadrature scheme is used to derive the solution. It is found that the length of the slippage zone and the receding contact angle of adhesives are the two most significant contributors to the total fracture energy of the decohesive zone. These results demonstrate that the mechanism of interfacial slippage plays a significant role in the adhesion and peeling behaviors of adhesives.     

Detachment of stretched viscoelastic fibrils

New experimental results are presented about the final stage of failure of soft viscoelastic adhesives. A microscopic view of the detachment of the adhesive shows that after cavity growth and expansion, well adhered soft adhesives form a network of fibrils connected to expanded contacting feet which fail via a sliding mechanism, sensitive to interfacial shear stresses rather than by a fracture mechanism as sometimes suggested in earlier work. A mechanical model of this stretching and sliding failure phenomenon is presented which treats the fibril as a nonlinear elastic or viscoelastic rod and the foot as an elastic layer subject to a friction force proportional to the local displacement rate. The force on the stretched rod drives the sliding of the foot against the substrate. The main experimental parameter controlling the failure strain and stress during the sliding process is identified by the model as the normalized probe pull speed, which also depends on the magnitude of the friction and PSA modulus. In addition, the material properties, viscoelasticity and finite extensibility of the polymer chains, are shown to have an important effect on both the details of the sliding process and the ultimate failure strain and stress. Electronic supplementary material Appendix B is only available in electronic form at and are accessible for authorised users.     

Z箍缩动态黑腔负载装配用胶粘剂

由于Z箍缩动态黑腔负载中的低密度聚合物泡沫柱具有多孔结构和极低的力学强度,在装配过程中对胶粘剂有一定的特殊要求。实验以聚氨酯丙烯酸酯为主体树脂,丙烯酸异冰片酯为活性单体,配以光引发剂和偶联剂制得了适用于低密度泡沫粘接用的紫外光固化胶粘剂。测试表明,所研制的胶粘剂的体积收缩率仅为2.25%,且具有较高的固化速率和适当的粘接强度,能够满足稳固、快速装配的要求。通过对粘接界面的观测发现,胶粘剂在诊断孔内没有明显的扩散,且在低密度致密结构泡沫中的扩散厚度较小,均匀性好。     

颜面赝复体粘接剂的红外光谱分析

传统的颜面赝复体粘接剂按其成分可分为聚丙烯酸酯类和有机硅类。以往对于颜面赝复体粘接剂性能的研究,多为粘接强度的测试,而有关这些粘接剂在粘接过程中的变化研究则较少见。文章测试了两种颜面赝复体粘接剂 (Epithane3及Secure2 Adhesive)在液态、半固态时的红外光谱。结果提示,Epithane3结固过程中有水分和残留氨的挥发,Secure2 Adhesive结固过程中表现为乙酸乙酯挥发。有机硅官能团是有机硅类和硅橡胶的粘接强度比聚丙烯酸酯类高的关键。两种粘接剂红外光谱主要吸收峰的峰位、峰形与结固前相同, 表明结固前后其主要化学成分和基本结构未发生变化。     

Thin films of polymer mimics of cross-linking mussel adhesive proteins deposited by matrix assisted pulsed laser evaporation

Mussels secrete specialized adhesives known as mussel adhesive proteins, which allow attachment of the organisms to underwater marine environments. Obtaining large quantities of naturally derived mussel adhesive proteins adhesives has proven to date rather problematic, thus, synthetic analogs of mussel adhesive proteins have recently been developed. We report deposition of 1:100 and 1:1000 poly[(3,4-dihydroxystyrene)-co-styrene)] mussel adhesive protein analogs by matrix assisted pulsed laser evaporation (MAPLE) using an ArF* excimer laser source. The deposited films have been evaluated for their antifouling behavior. The MAPLE-deposited synthetic mussel adhesive protein analog thin films are homogenous and adhesive, making the use of these materials in thin film form a viable option.     

8～14μm波长低红外发射率涂料的研究

研究了红外隐身涂料粘合剂的物理和化学性能,以及红外隐身涂料粘合剂、填料、颜料颗粒的红外发射率。通过研究发现,铝粉和氧化铅具有较低的发射率,并得到了以有机硅清漆和EPDM(三元乙丙橡胶)接枝聚合物为基体的低红外发射率涂料,它有助于对红外隐身涂料粘合剂、填料、颜料颗粒的选择。     

杂化溶胶改性紫外光固化胶粘剂的研究

 以自制的杂化溶胶对紫外光固化丙烯酸酯胶粘剂进行改性，得到了具有高粘接强度，对丙酮、乙醇、氯仿等具有明显的耐溶剂性的紫外光固化胶粘剂。实验发现：活性稀释剂中含有较多的羟基、羧基时，此胶粘剂对玻璃的粘接强度较高；胶层粘接力随杂化溶胶用量的增加先增大，后减小，当杂化溶胶中的固体质量为光敏树脂的60％时，胶粘剂的剪切强度达到最大（12MPa）。     

光学胶粘剂

本文介绍了GGJ型光学光敏胶粘剂的主要材料、配比和主要性能。并与其他一些光学胶作了对比,结果表明,该胶可广泛地应用于各种光学仪器,尤其对大批量照相机生产更为适用。该胶毒性小,操作方便,效率高,可提高工效5倍以上。     

胶粘剂对石英音叉剪切力控距的影响

粘接音叉和光纤探针的胶粘剂对由石英音叉和光纤探针构成剪切力控距体系的品质因数有明显的影响。通过对比不同胶粘剂的物理特性 ,选择了适合于粘接音叉和光纤探针的胶粘剂。研究发现 ,室温快速固化环氧树脂胶粘剂HY 91 4 ,GHJ光学用环氧型胶粘剂 (Opticalepoxy)和 50 2胶能满足实验要求。理论分析指出 ,对于同样的音叉和光纤探针来说 ,胶粘剂的密度和用量是影响音叉 探针体系品质因数的主要因素     

The role of alumina nanoparticles in epoxy adhesives

Both untreated and calcined fumed alumina nanoparticles were dispersed into an epoxy-based adhesive at various percentages. The glass transition temperature of the nanofilled adhesives increased up to an optimal filler loading and then decreased, probably due to concurrent and contrasting effects of chain blocking and reduction of the crosslinking degree. Tensile modulus, stress at break, and fracture toughness of bulk adhesive were positively affected by the presence of untreated alumina nanoparticles at an optimal filler content. Mechanical tests on single-lap aluminum bonded joints indicated that untreated alumina nanoparticles markedly improved both the shear strength and fatigue life of the bonded joints. In particular, the shear strength increased by about 60% for an optimal filler content of 1 vol.%, and an adhesive failure mechanism was evidenced for all the tested specimens. Concurrently, a relevant decrease of the equilibrium contact angle with water was observed for nanofilled bulk adhesives. In summary, alumina nanoparticles can effectively improve the mechanical performances of epoxy structural adhesives, both by increasing their mechanical properties and by enhancing the interfacial wettability with an aluminum substrate.     

Silica Nanoparticles as Adhesives for Biological Tissues? Re‐Examining the Effect of Particles Size,Particle Shape,and the Unexpected Role of Base

Development of new, effective, and patient‐friendly adhesives for biological tissues is important for medical and surgical practices such as bleeding control and organ repairing. While some commercially available silica nanoparticles such as LUDOX SM‐30 have shown adhesive properties for biological tissues, the role of inorganic base present in the adhesive properties of the silica nanoparticles has not been examined. Moreover, it remained unclear how the size and the shape of silica nanoparticles affect the adhesion properties. To address these questions, synthesis and characterization of a series of uniform silica nanostructures with different sizes and shapes is carried out. Unexpectedly, none of the synthesized silica nanostructures without additional inorganic base shows adhesion properties against liver tissues. Such surprising phenomena motivate to examine other factors in the commercial silica nanoparticles as tissue adhesives, and reach a conclusion that the inorganic base plays a key role in the adhesion properties. It is believed that this study answers the important question whether silica nanoparticles can act as biological adhesives or not. The conclusion also gives a lesson to other scientists and engineers in design and exploration of new biological adhesives.     

Attaching Planar Waveguide Dies to Aluminum Using Low-Stress Thermal Conductive Adhesives

We analyzed stress and heat transfer in attached planar waveguides. Die attaching adhesives were known to be the key to avoiding stress buildup in and dissipating heat from waveguides. When adhesives have a shear modulus of less than 1 MPa and a thermal conductivity of 2 w/mk, a 0.1-0.2-mm-thick layer of adhesive can eliminate stress-related effects and efficiently dissipate 30-50 mW/mm² of heat, even if aluminum is used as a substrate. Supersoft thermal conductive adhesives were thus developed and used to attach 60-mm-long AWG dies to aluminum with excellent results.     

Measuring the critical energy release rate in mode II of tough,structural adhesive joints using the tapered end-notched flexure (TENF) test

This paper shows and discusses results of the Tapered End-Notched Flexure (TENF) test, investigating the fracture behaviour of high-strength structural adhesive joints under shear loading. The TENF test has been previously applied to brittle joints by different authors and has been re-designed to be applicable to ductile adhesives in the presented work. Furthermore, the tests are performed at two velocities, a quasi-static and a dynamic one, to investigate rate effects on the fracture behaviour of the joint. All experimental work has been performed using the structural adhesive DOW Betamate 1496V.     

The effect of silane incorporation on a metal adhesive interface: A study by electron energy loss spectroscopy

A silane-based adhesive formulation, used in the aerospace industry, was studied using sub-nanometre spatially resolved energy loss spectroscopy, as a function of the concentration of silane used in the adhesive. The changes in the relative oxygen concentration and the occupancy of p-type states in the oxygen density of states reveal the existence of a composite layer between the aluminium and the epoxy resin. This composite layer is prevalent in the 1% (w/w) organosilane sample, whilst it is smaller or absent for the 0.5% and 2% (w/w) silane concentration. These observations correlate well with the observed macroscopic durabilities observed when these adhesives are used for the structural adhesive bonding of aluminium aerospace alloys.     

Thermosets as compatibilizers at the isotactic polypropylene film and thermomechanical pulp fiber interphase

The objective of this study was to improve interfacial adhesion properties at the interface of thermomechanical pulp (TMP) fiber and isotactic polypropylene (iPP) using thermoset adhesives such as phenol formaldehyde (PF) and urea formaldehyde (UF). This study also attempted to achieve fiber-to-fiber adhesion using thermoset adhesives before the molten iPP would flow into the fiber web. The fracture surfaces with thermoset adhesive showed identical differences in terms of fracture modes at the interface. An increased TMP fiber failure was observed with increased thermoset quantity at the interface. Using one percent resin content of weight fraction of TMP fiber handsheet, the tensile strength properties increased almost two fold higher than the strength of control samples. Additional adhesive contents of three and five percent showed gradual strength enhancement. However, the enhanced strength was statistically insignificant. UF resin showed slightly better strength performance over PF resin. This result may be caused by solid contents and additional pigments of resins.     

Castor Oil-Based Polyurethane/Epoxy Intercross-linked Polymer Network Adhesives for Metal Substrates

Castor oil based polyurethane (CO-PU) was first synthesized from castor oil and 4, 4’-diphenyl-methane-diisocyanate (MDI). Then, a series of CO-PU/epoxy (EP) intercross-linked polymer network (ICPN) adhesives for metal substrates were prepared by a sequential method. The functional groups, tack -free time, mechanical properties, adhesive properties, and thermal stability were studied. Fourier transform infrared spectroscopy analysis indicated that an ICPN structure was formed through the introduction of CO-PU into EP. Results of adhesive measurements showed that the maximal value of lap shear strength was achieved at the CO-PU content of 20%. Thermogravimetric analysis results indicated that thermal stability of the adhesive film decreased with increased CO-PU content.     

Improving Epoxy Adhesives with Zirconia Nanoparticles

Zirconia nanoparticles were synthesized by a sol–gel route and dispersed into an epoxy base for structural adhesives. Nanoparticles were used as-synthesized or after calcination. Moreover, the effect of silane functionalization was also investigated. According to preliminary tensile mechanical tests on bulk nanocomposite samples, calcined and untreated zirconia nanoparticles were selected for the preparation of adhesives with various filler contents. The glass transition temperature increased up to a filler content of 1 vol% and then decreased, probably due to the concurrent and contrasting effects of chain blocking and reduction of the crosslinking degree. Also tensile modulus, stress at break and fracture toughness of bulk adhesives samples were positively affected by the presence of an optimal amount of zirconia nanoparticles. Mechanical tests on single lap aluminium bonded joints indicated that zirconia nanoparticles led to relevant enhancements of the shear strength of the joints. In particular, the shear strength increased by about 60% for an optimal filler content of 1 vol%, and an adhesive failure mechanism was evidenced for all the tested specimens. Concurrently, a significant decrease of the equilibrium contact angle with water was observed for adhesives containing zirconia nanoparticles. It can therefore be concluded that the addition of zirconia nanoparticles can effectively improve epoxy adhesives, both by increasing their mechanical properties and by enhancing the interfacial wettability with an aluminium substrate.     

Raman and infrared analysis of glues used for pottery conservation treatments

The conservation of ceramics and glass involves the repair or the restoration of broken and fragmented artefacts with polymer adhesives and gap fillers. In the past, many different adhesives had been used. Re‐restoration is often required and the fast identification of adhesive residues on objects would be very useful to define the best of way to remove them, in particular to avoid the use of noxious chemicals. Sixteen pottery artefacts restored during the 19th and 20th centuries at the Musée National de Céramique in Sèvres have been analysed by non‐destructive Raman microspectroscopy. For comparison purposes, the artefacts were also sampled in order to acquire infrared (IR) absorption spectra in KBr pellets. Modern adhesives (methyl metacrylate/acrylate, vinyl acetate, polychloroprene, methyl 2‐cyanoacrylate and diglycidylether biphenol) were also characterised with the same methods. IR and Raman spectra were obtained for all ancient glue residues, but among the 16 analysed items, only 7 adhesives have been identified unambiguously, and an assignment proposed for 4 others solely on the basis of the Raman signature. Copyright © 2009 John Wiley & Sons, Ltd.     

Investigation of adhesive–dentin interfaces using Raman microspectroscopy and small angle X‐ray scattering

Human dentin specimens were treated with two different etch‐and‐rinse adhesives, Single Bond 2 (SB2) and Prime & Bond NT (PBNT), and two composite resins, TPH and P60. Cross‐sectional samples, approximately 1 mm thick, were analyzed with Raman line mapping and imaging across the dentin–adhesive–composite interface. The integrated intensities of selected bands associated with adhesive, organic material, composite and hydroxyapatite of dentin were calculated to determine the distribution of adhesive infiltration into demineralized dentin. The results were compared with the enamel‐adhesive composite interface. The demineralized zone was smaller in the enamel‐adhesive interface than in the dentin–adhesive interface. The region of collagen‐adhesive crosslinking was wider in the PBNT adhesive than in the SB2 adhesive. However, a gap at the dentin–PBNT composite interface, which was not observed at the dentin–SB2 composite interface, might compromise the dentin–restoration bond. K‐means cluster analysis of the Raman images confirmed the findings. The ultrastructure of the dentin–resin interface was studied using scanning electron microscopy. Small‐angle X‐ray scattering was also applied to reveal and quantify fine‐scale structural features. SB2 adhesive was found to diffuse more into demineralized dentin along with greater nanosized aggregations in the hybrid layer. Copyright © 2011 John Wiley & Sons, Ltd.     

The measurement of cohesive and interfacial toughness for bonded metal joints with epoxy adhesives

The types of crack growth in adhesive joints are reviewed and three are identified, namely central cohesive, asymmetric cohesive and interfacial. Test methods for measuring fracture toughness associated with these cracks are then outlined and include a Tapered Double Cantilever Beam (TDCB) test for a central cohesive crack and peel tests on flexible laminates for the other types of crack. In particular, fixed arm and mandrel peel tests are used. Two aerospace adhesives are used to prepare test specimens in order to conduct these tests. For one of these adhesives, all three types of crack growth were recorded and this provided an opportunity to make detailed comparisons of the three associated fracture toughness values. Of particular interest was the use of the mandrel peel method because it enabled a fracture transition (asymmetric cohesive to interfacial fracture) to be observed during the test. The fracture toughness value associated with a central cohesive crack was similar in magnitude to that for an asymmetric cohesive crack. However, the fracture toughness for interfacial fracture was much lower, but similar in magnitude to the expected value of half the fracture toughness from a TDCB test.