Debond-on-Demand Adhesives
Researchers at AMI have developed a polymer-based material that can bond and debond-on-command when placed under ultraviolet light.
Researchers at the Adolphe Merkle Institute have developed a polymer-based material that can bond and debond-on-command when placed under ultraviolet light. Their findings were published as the Editors Choice in a recent issue of ACS Applied Materials & Interfaces. The reversible adhesives could be used to bond and debond materials used in automotive parts, metal and glass surfaces, packaging materials, medical devices, and many other applications. The proof-of-concept studies carried out can now be adapted and further developed for commercial use.
Adhesive: Picture of a supramolecular adhesive bonding
two glass slides together and illuminated with UV light. Pictures courtesy
Christian Heinzmann for Adolphe Merkle Institute, University of Fribourg,
Switzerland.
The new materials were created by a mechanism known as supramolecular assembly. Unlike conventional polymers, which consist of long, chain-like molecules with thousands of atoms, they are composed of smaller molecules, which are assembled into longer, polymer-like chains using metal ions or hydrogen bonding motifs to link the small components together and create a “quasi-crosslinked” network structure. The result: the new materials, which the scientists call “supramolecular polymers”, behave in many ways like normal polymers. However, when irradiated with intense ultraviolet light, the supramolecular structures disassemble, resulting in a “liquid-like” material state. The supramolecular assemblies reform again as soon as the stimulus is removed.
When used as an adhesive, the material is able to bond objects together under ambient conditions. Upon exposure to an external stimulus – such as ultraviolet light or heat – the liquid-like state of the material possesses no cohesive properties anymore and the bonded objects can be separated easily. As soon as the external stimulus is removed, the original material properties are restored and it can be re-used as an adhesive. The process of bonding and debonding can be performed multiple times without losing the adhesive properties of the original material.
Reversible adhesive: Pictures displaying the bonding and debonding properties of the
supramolecular adhesive. Under ambient conditions, the rubbery supramolecular
adhesive is able to glue objects together such as glass slides (top). Upon
irradiation with UV light, the supramolecular polymer liquefies and loses its
adhesive properties (bottom). As soon as the light is removed, the material solidifies
again and the original properties are restored. The whole process is fully
reversible and can be repeated multiple times. Pictures courtesy Christian
Heinzmann for Adolphe Merkle Institute, University of Fribourg, Switzerland.
Schematic supramolecular: Schematic representation of the molecular
design of the supramolecular adhesive. The supramolecular assembly consists of
comparatively short chain-like molecules (black) with a functional group on
each end (blue), which can be connected by a metal ion (grey), extending the
chain length. The connected / disconnected states can be influenced, for
example with ultraviolet light or heat. Under ambient conditions (left) the
supramolecular polymer behaves like a regular rubbery material, whereas when
exposed to a stimulus, the material liquefies (right). As soon as the stimulus
is removed, the supramolecular assemblies reform again, restoring the original
material properties. This process is reversible and can be repeated multiple
times. Schematic courtesy Christian Heinzmann for Adolphe Merkle Institute,
University of Fribourg, Switzerland.