Modern integrated microelectronic devices are sometimes poorly repairable and difficult to recycle. Debondable adhesives play a key role within the transition to a circular economy with sustainable resources, less waste, and intelligent repair/recycling strategies. Within the journal Angewandte Chemie, a research team has now introduced a technique for making adhesives that could be deactivated “on command.”
Their inspiration got here from the masters of underwater adhesion: mussels. Mussel-inspired adhesives have been developed before. These recent versions are based on thiol-catechol polyaddition, which forms polymers with adhesive thiol-catechol connectivities (TCC, thiol-substituted six-membered fragrant rings with two neighboring OH groups that are accountable for the strong adhesive properties). The trick is that when the catechol groups within the adhesive polymers are oxidized to quinones (six-membered rings with two oxygen atoms sure by double bonds), the strength of adhesion decreases dramatically.
Changing the essential framework of the monomers allows for control over the properties of the polymers. Kannan Balasubramanian, Hans Börner, and their team at Humboldt University zu Berlin, the Leibniz Institute for Analytical Sciences (ISAS, Berlin, Germany), Universidad Nacional de General San Martin (Buenos Aires, Argentina), the Fraunhofer Institute for Applied Polymer Research (Potsdam-Golm, Germany), and the corporate Henkel (Düsseldorf, Germany) have now produced two various kinds of TCC adhesives with strong adhesion and shear strength.
Biobased, peptidic biscatechol precursors of DiDOPA, which is similarly present in mussels, were compared with their fossil-based analog. Each adhesives also function under water and are insensitive to atmospheric oxygen and weak oxidizing agents. Nevertheless, they lose their stickiness through oxidation with the strongly oxidizing sodium periodate (NaIO4), in order that the adhesive residues could be easily peeled or wiped off the substrate in a single piece.
While the oxidation of the fossil adhesive inactivates the catechols, but at the identical time makes the adhesive more hydrophobic, the biobased type shows the deactivation without becoming dramatically more hydrophobic as a result of a wide range of other peptide functionalities. Börner explains: “The multifunctionality is typical of biomaterials, during which often only the important thing functionalities are switched off and never much else changes in the fabric. This circumstance enables a dramatically more efficient de-adhesion mechanism, which reduces the adhesive strength of the bio-based type by 99%.” The explanation for the poorer deactivation (60%) of the fossil-based adhesive lies within the compensation, as hydrophobic polymers are also excellent adhesives.
In the long run, the consortium is working on replacing chemical oxidation with direct electrochemical oxidation, which may very well be interesting for the repair of cell phones, for instance.
