(ORDO NEWS) — Scientists in Japan have developed a new adhesive that can be turned on and off at will. Caffeic acid is used to make the glue, which forms and breaks cross-links under the influence of light of different wavelengths. When irradiated with ultraviolet light at a wavelength of 365 nanometers, the adhesive turns into a strong film that holds at room temperature with a shear bond strength of up to 7.2 MPa.
However, when irradiated with ultraviolet light with a wavelength of 254 nm, the crosslinks are destroyed, and the adhesive returns to its original state, which allows it to be reused as new. The researchers embedded magnetic nanoparticles in the adhesive, which heat up when a magnetic field is applied, bonding the adhesive to the base. This material can be used in a wide range of applications, allowing products to be more easily disassembled into their component parts at the end of their service life and converted into new products.
Adhesive development is tricky business, as it has to balance two conflicting properties: how well they stick together and how easily they separate from each other. When one property is strengthened, another is usually sacrificed. The ideal adhesive should be one that holds firmly during use but can be separated on demand to correct mistakes or when the product is no longer needed.
Scientists at Japan’s National Institute of Materials Science (NIMS) have developed an adhesive that does just that. The key component is caffeic acid, which is able to form and destroy crosslinks under the influence of light of different wavelengths. In this case, the experts made a polymer containing caffeic acid, applied it to the surface and irradiated with ultraviolet light with a wavelength of 365 nanometers (nm). As a result, the polymer hardens into a strong film that holds at room temperature with a shear bond strength of up to 7.2 MPa.
When adhesion is no longer needed, the film can be exposed to 254 nm ultraviolet light, which breaks down the crosslinks and returns it to its original state. At the same time, the film does not leave marks on the surface and does not lose its adhesive properties, which allows it to be reused like a new one.
The researchers subjected the adhesive to a series of tests, including repeatedly bending samples and lifting a 40 kg (88 lb) load, which it held for 72 hours without any sign of breaking. In other cases, glue was used to repair cracked silicone tubes, then high pressure water was run through them and there were no leaks.
In subsequent tests, the team demonstrated that the material could be used even underwater. Magnetic nanoparticles were embedded in the adhesive, which, when a magnetic field is applied, heat up, bonding the adhesive to the base.
According to experts, this material can be widely used, making it easier to disassemble products into their component parts at the end of their service life and turn them into new products.
According to Dr. Emre Kizilkan, Postdoctoral Fellow in the Department of Mechanical Engineering at Imperial College London, “The development of a photosensitive adhesive that can be activated and deactivated on demand is a significant breakthrough as it provides a reversible bonding mechanism that can be used in various fields such as manufacturing, electronics and biomedicine”.
The study is published in the journal Advanced Functional Materials.
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