Background Pressure-sensitive adhesive (PSA) is a common means of adhesion used in various fields. Examples of daily use include adhesive tape or sticky paper. PSAs are also used in industrial fields such as building materials and cars. However, the phenomenon of adhesion is complex because of the many factors involved, such as surface free energy, viscoelasticity, and cohesion. Many studies have been conducted to investigate the nature

The development of low material-consuming adhesion techniques for different kinds of materials such as polymers and metals is important for the realization of sustainable societies. This study demonstrates that coating layers, expected to be formed as self-assembled monolayers, of silane coupling agents can act as adhesion layers at the polymer film-metal plate interfaces. Polyimide films were alkaline hydrolyzed to generate carboxy groups on their surfaces, whereas titanium plate surfaces were treated with the aminosilanes to form their coating layers thereon. These modified surfaces were placed in contact with each other and then hot pressed, which resulted in adhesion between them. An examination of the adhesion strength using lap shear tests and surface characterization of the prepared surfaces using X-ray photoelectron spectroscopy and other techniques indicated the formation of ionic bonds and/or amide bonds between the carboxy groups of the PI film surfaces and the amino groups immobilized on the titanium plate surfaces. The activation of the carboxy groups using N-hydroxysuccinimide resulted in adhesion obtaining a water-resistant property, which supported the increase in amide bond formation. On the basis of the results, the adhesion mechanism and the possible breaking points upon the breaking of adhesions are proposed.

Understanding the adhesion process between a rigid material (filler) and a viscoelastic material is important for designing an enhanced industrial material. However, the adhesion process is not simple because the properties of the adhesive, adherend, and interface are intricately influenced by this process. Here we investigate the adhesion of microspheres onto rubber films to clarify the dominant factor in the adhesion process. A rubber meniscus first forms on the sphere surface, followed by sedimentation of the sphere into the rubber film. This sedimentation is even observed when the surface free energy of the sphere is lower than that of the rubber film, which indicates that the driving force of meniscus formation obeys Young’s equation on a tangential line of the sphere. The dominant factor of the sedimentation behavior is investigated by using atomic force microscopy force–sample deformation curve measurements and creep tests on the rubber films. These experimental results demonstrate that the adhesion process is strongly dominated by the viscoelastic property of the bulk rubber as opposed to the sphere and interface properties.