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Posted: July 25, 2006
Bonding and de-bonding on command
(Nanowerk News) Adhesives are supposed to harden quickly and reliably – and connection should be debondable without difficulty once they have done their job. Fraunhofer researchers have developed the first adhesive to reconcile these contradictory requirements.
Gluing plastics is a challenge. Adhesives are normally hardened by heat, but heat-sensitive plastics are often unable to withstand high temperatures. Two-component adhesives are therefore mixed only shortly before use, and harden without heat over a long period of time. Adhesives are also supposed to be strong – yet when repairs have to be made or bonded parts should be re-used, the reverse is true. We want the adhesive bonds to be debondable as easily as
“The adhesives contain the MagSilica® filler, which is nano-structured and can be stimulated with high frequencies,” says Dr. Andreas Hartwig, head of the IFAM’s Adhesives and Polymer Chemistry department. “In the high-frequency field, the adhesive hardens immediately without any exposure to external heat sources. In the same way, the adhesive connections can be debonded at the touch of a button.” The researchers have managed to do this by mixing a powder of super-paramagnetic particles into the adhesive. These particles consist of iron oxide embedded in nanoparticles of silicon dioxide. When the scientists expose the adhesives to a high-frequency alternating magnetic field, the particles oscillate and heat the adhesive. This causes both one- and two-component adhesives to harden within seconds. “The bonds can be dissolved in a similar way,” Hartwig confides. “We expose the adhesive bond to another high-frequency magnetic field. This field has the same frequency as during hardening, but a higher intensity.” For the method to work, at least one of the components to be bonded must be electrically non-conducting.
The scientists were able to demonstrate the principle on various combinations of materials and different adhesive base formulations. Now the researchers are working to implement the results in commercial adhesives and products that contain them.