Modern microelectronic devices are often challenging to repair and recycle. The use of debondable adhesives is crucial for promoting a circular economy that focuses on sustainable resources, reducing waste, and enhancing repair and recycling methods. Recently, a research team has developed a technique for creating adhesives that can be turned off “on command.”
Modern microelectronic devices often face difficulties in repair and recycling. Debondable adhesives are essential for fostering a circular economy aimed at sustainable resource use, waste reduction, and better repair and recycling strategies. A research team has introduced a method to create adhesives that can be deactivated “on command,” as detailed in the journal Angewandte Chemie.
The researchers drew inspiration from mussels, which are known for their exceptional underwater adhesive abilities. Previous efforts have resulted in mussel-inspired adhesives, but these latest versions utilize thiol-catechol polyaddition. This process creates polymers that have strong adhesive connections (TCC) that feature thiol-substituted six-membered aromatic rings with two adjacent OH groups, contributing to their robust adhesive characteristics. The unique aspect of this invention lies in how the adhesive’s strength significantly diminishes when the catechol groups get oxidized to quinones, which are six-membered rings with double-bonded oxygen atoms.
By altering the basic structure of the monomers, the researchers can dictate the properties of the resulting polymers. Kannan Balasubramanian, Hans Börner, and their colleagues from Humboldt University zu Berlin, the Leibniz Institute for Analytical Sciences (ISAS) in Berlin, Universidad Nacional de General San Martin in Buenos Aires, the Fraunhofer Institute for Applied Polymer Research in Potsdam-Golm, and Henkel in Düsseldorf, have developed two distinct types of TCC adhesives that showcase strong adhesion and resistance to shear.
They compared biobased peptidic biscatechol precursors of DiDOPA, which mimic mussel characteristics, to their fossil-based counterparts. Both types of adhesives work underwater and are unaffected by atmospheric oxygen and mild oxidizing agents. However, they can lose their adhesion when exposed to strongly oxidizing sodium periodate (NaIO4), allowing the adhesive residues to be easily removed from surfaces in one piece.
While the oxidation of the fossil-based adhesive deactivates the catechols and makes it more hydrophobic, the biobased version deactivates without a significant increase in hydrophobicity thanks to its varied peptide functionalities. Börner notes, “Multifunctionality is typical in biomaterials, where often only essential functions are disabled while the material remains largely unchanged. This allows for a markedly more efficient de-adhesion process, reducing the adhesive strength of the biobased type by 99%.” In contrast, the fossil-based adhesive experiences a lesser deactivation (60%) mainly because hydrophobic polymers tend to be strong adhesives as well.
Looking ahead, the research team aims to substitute chemical oxidation with direct electrochemical oxidation, which could offer exciting possibilities for repairing devices like cell phones.
