A team of researchers from the Case Western Reserve University headed by Stuart J. Rowan, a research team from the Army Research Laboratory at Aberdeen Proving Ground headed by Rick Beyer and another team of researchers at the Adolphe Merkle Institute of the University of Fribourg headed by Christoph Weder have developed a polymer-derived substance that can heal on its own when exposed to UV light for not more than a minute. The research has been published in Nature on April 21 issue.
According to the researchers, the polymer-based substance is not yet ready for commercial utilization. However in the future, these substances could be utilized in varnishes for furniture and floors, motor vehicle paints and several other applications.
Stuart Rowan, Director of the Institute for Advanced Materials at Case Western Reserve University and Professor of Macromolecular Engineering and Science, stated that the polymers include a Napoleon Complex and the distinct weak molecular interactions offer innovative behavior to these tiny polymers.
Christoph Weder, Director of the Adolphe Merkle Institute and Professor of Polymer Chemistry and Materials, mentioned that the molecular layout of the polymers enable them to alter their characteristics when exposed to intense UV light.
The new polymer-based substances were developed by means of supramolecular assembly. When compared to traditional polymers, which include extensive, chain-like molecules featuring thousands of atoms, these substances are made of tiny molecules which are grouped into lengthy, polymer-resembling chains by utilizing metal ions as ‘molecular glue.’ The resulting new substances are termed as ‘metallo-supramolecular polymers’ and in several ways show similar behavior as conventional polymers. However when exposed to high dose of UV light, the grouped structures are momentarily separated and the original solid substance is converted into liquid form, which is capable of flowing easily. When radiation is turned off, the substance re-groups into a solid form and the original characteristics are reinstated.
The scratches found in the polymers were repaired by using lamps, which are similar to those used by dentists to treat fillings. The researchers found that wherever they moved the UV light, the scratches filled up and vanished, leaving no trace on the surface. Experiments confirmed that the scientists could continually scratch and restore the substances in the same spot.
According to Mark Burnworth, a student at Case Western Reserve University, the enhanced control offered by the UV light enabled them to aim only at the flaw and leave the remaining substance undisturbed.
The scientists methodically studied several new polymer-based substances to determine an enhanced combination of mechanical characteristics and curing capability. They determined that metal ions supporting the grouping process through weaker chemical interactions serve as the light-sensitive molecular glue. They also established that the substances that grouped in the most organized microstructures had superior mechanical characteristics. However as structural order reduced, the healing efficiency improved significantly.
Beyer mentioned that understanding these associations is crucial to enhance the lifespan of coatings customized to distinct applications. Rowan stated that the researchers would apply the concepts to develop a coating that could be used in industrial applications.
The US Army Research Laboratory’s Army Research Office, Adolphe Merkle Foundation and the US National Science Foundation sponsored the research.