Applied Adhesion Science最新文献

Gecko’s foot hairs exhibit significant frictional anisotropy that enables a strong foot grip in a specific direction and an easy detachment in the opposite direction. In this study, we fabricate adhesive devices with frictional anisotropy mimicking gecko’s foot hair based on oblique micro-beam arrays. The devices adhesion force is strongly anisotropic along the beam tilting direction and depends on the stress distribution at the contact area which, in turn, is affected by the geometry of the beam tips. This dependence is investigated by fabricating and testing micro beam arrays with various tip shapes.

Double cantilever beam (DCB) tests under impact loading conditions were conducted using a falling-wedge impact test machine and a high-speed camera. The change in mode I fracture energy G _IC was investigated in comparison with the results obtained under the quasi-static loading condition. Two types of adhesives with significantly different mechanical properties were used for the DCB tests, and the change in rate dependency of the adhesive types was observed. Adhesively bonded joints have been widely used in various engineering products, such as automobiles, ships and airplanes. The strength of the joints is important for product safety. To evaluate the mode I fracture energy of adhesively bonded joints, DCB tests have been standardized under the quasi-static loading condition. Additionally, several tests have been proposed to evaluate the impact resistance of the joints. However, impact loading makes it difficult to evaluate the fracture energy accurately because of the dynamic effects. Therefore, specialized evaluation methods for dynamic fracture must be considered, and a load-independent analysis of the fracture energy was used to avoid load measurement problems due to the dynamic effects in this study.

This paper reports on the adhesion characteristics between microspheres and rubber surfaces. Silica, polystyrene, and poly(methyl methacrylate) microspheres were deposited on cis-1,4-polybutadiene (BR) films. A BR meniscus formed on the sphere surfaces when the film thickness was less than the diameters of the spheres. Additionally, the attractive forces acting on the spheres in the direction of the BR films were examined via atomic force microscopy. Sedimentation of the spheres occurred for films with thicknesses much greater than the diameters of the microspheres in all systems. Interestingly, this wetting process occurred even in the silica/BR system, despite the incompatibility of these materials. The driving force for meniscus formation is the difference between the surface free energy of BR (γ _BR) and that of the spheres (γ _sphere). For all systems, γ _BR is lower than γ _sphere, i.e., the BR surface is more stable than those of the spheres, and thus a meniscus forms to stabilize the system. Once a meniscus formed, a downward force acted on the spheres to embed them into the BR film. Sedimentation eventually ceased when the angle between the tangential line of the sphere and the rubber surface became equal to the equilibrium contact angle determined by Young’s equation. Interestingly, the sedimentation behavior was nearly identical for spheres with various surface free energy values except in terms of their final positions. The same sedimentation phenomena were studied with crosslinked BR films. In contrast to the experiments performed using various types of spheres, the sedimentation behavior varied with different rubber characteristics. The results of these studies indicate that the sedimentation behavior mainly depends on the physical properties of the rubbers used, although the physical properties of the spheres are in determining their final depth.

To develop an adhesion system satisfying both constant adhesion strength during use and quick debonding ability during a dismantling process.

Adhesive properties were investigated for the random and block copolymers consisting of 1-isobutoxyethyl acrylate (iBEA), 2-ethylhexyl acrylate (2EHA), and 2-hydroxyethyl acrylate (HEA) as the dismantlable pressure-sensitive adhesives in the presence of a photoacid generator in response to dual external stimuli of photoirradiation and post baking.

The use of LED combined with a new photoacid generator SIN-11 was enable us to achieve a rapid dismantling process during UV irradiation within several minutes. The protection of the ester alkyl group in the iBEA repeating unit to give an acrylic acid unit was suppressed by the introduction of isobornyl acrylate (IBoA) as the additional unit into the copolymer of iBEA, 2EHA, and HEA. While IBoA‐containing block copolymer showed a constant adhesive strength during photoirradiation as the single external stimulus, deprotection was immediately induced by the subsequent heating, leading to a significant decrease in the adhesive strength.

The copolymer including the iBEA and IBoA units was revealed to function as the highly sensitive adhesive materials for dual-locked dismantlable adhesion.

Adhesion hysteresis was investigated with the energy dissipation in the contact experiments between a spherical glass lens and a polydimethylsiloxane (PDMS) block. The experiments were conducted under step-by-step loading–unloading for the spontaneous energy dissipation. The force, contact radius, and displacement were measured simultaneously and the elasticity of the PDMS was confirmed. The work of adhesion was estimated in the loading process of the strain energy release rate. The total energy dissipation has been observed to be linearly proportional to the contact radius in the unloading process. The approximately constant gradient of the energy dissipation for each unloading process has been found. The result would provide how the dissipation is induced during the unloading as some interfacial phenomena. The fact has been discussed with some interfacial phenomena, e.g., the adsorbates on the surface, for the mechanism of adhesion hysteresis.

Effects of mixed micro and nano silica particles on the dynamic stiffness, stress transmissibility, and energy absorption of the epoxy composite were investigated using the split Hopkinson pressure bars. It was found that the dynamic stiffness significantly increased with silica weight fraction regardless of its sizes and composition ratio. However, the effect became less significant as the temperature approached T _g . It was also found that mixed micro and nano silica particles decreased both the epoxy dynamic stiffness and the stress transmissibility, and increased the energy absorption. The optimum composition ratio was found to maximize the energy absorption while maintaining high stiffness performance of epoxy. The results obtained in the present work can be used to design the performance of epoxy/silica adhesive for appropriate applications.

The objective of this study was to evaluate the coumarin-based iodonium hexafluoroantimonate (P3C-Sb) in the polymerization kinetics of an experimental model adhesive resin both in presence of solvent and acid monomer content. A monomer mixture based on Bis-GMA, TEGDMA and HEMA was used as a model adhesive resin. Initially a screening was performed to evaluate P3C-Sb concentrations (0.25, 0.50, 1, 2, 4?mol%). Four photoinitiator systems using P3C-Sb at 2?mol% were evaluated: CQ?+?EDAB (control), P3C-Sb?+?CQ, P3C-Sb?+?EDAB and P3C-Sb?+?EDAB?+?CQ. Additionally, the performance of the photoinitiator systems in the presence of ethanol and acidic monomer at four different concentrations (0, 10, 20, 40 wt%) were evaluated. Real-time Fourier transform infrared spectroscopy was used to evaluate degree of conversion (DC) and rate of polymerization (RP). The ternary initiation system P3C-Sb?+?CQ?+?EDAB showed similar DC and RP to CQ?+?EDAB into the model adhesive resin without ethanol, however, in the presence of solvent, P3C-Sb?+?CQ?+?EDAB showed the highest polymerization kinetics. An inhibitory polymerization effect was observed when a solvent was introduced to adhesive resin using CQ?+?EDAB. Polymerization reaction was affected by the presence of acidic monomer irrespective of initiation system used. Adhesive resins with CQ?+?EDAB and P3C-Sb?+?CQ?+?EDAB as initiation systems showed similar DC to CQ?+?EDAB in presence of acidic monomer. The use of P3C-Sb as a third component of the initiation system seems to be an interesting alternative to improve the polymerization kinetics of simplified dental adhesives which showed to be less sensitive to the residual presence of solvent before photoactivation and it was similar polymerization behavior to CQ?+?EDAB in presence of acidic monomer.

This study evaluated the effect of aging methods on the bond strength of etch-and-rinse adhesive systems to dentin cavities. Eighty bovine incisors were used to prepare dentin cavities, which were bonded with different adhesive systems [Adper Scotchbond Multipurpose (SBMP), and Adper Single Bond 2 (SB)], and restored with composite resin. The specimens were stored in water for 24?h, and subjected to each aging method (n?=?10): control group (not exposed to additional aging), thermal cycling (TC) (10,000 cycles; at temperatures of 5, 37, and 55?°C), mechanical loading (ML) (100,000 cycles; Hz; 60?N load), and TC?+?ML. The push-out bond strength test was performed using a universal testing machine. Failure modes were evaluated by scanning electron microscopy. Data were analyzed by two-way ANOVA and Tukey’s test (α?=?0.05). For SBMP, only TC?+?ML decreased the bond strength compared to control group. For SB, all aging methods decreased similarly the bond strength compared to control group. A high number of adhesive failures were observed. Therefore, SB was sensitive to all aging methods, whilst only TC?+?ML was able to decrease the bond strength for SBMP.

An experimental investigation was performed to study the effect of surface roughness and oxidation on the shear strength of single-lap-joints of AA6061, AA7075 aluminum alloys and an?AISI 1080 steel?alloy bonded with two different epoxy adhesives. An optimum surface roughness that provided the maximum shear strength was obtained for all the alloys at room temperature. The variation of the shear stress due to the different heat treatment temperatures revealed that the oxides developed on the alloy surfaces adversely affected the adhesive shear strength. The bulk concentration of magnesium of the aluminum alloys were also observed to affect the adhesive shear strength of the joints.