According to a study published in the journal Nature Communications, the team created a new system – inspired by photosynthesis – that uses visible light to generate reactive radical species that can trigger polymerization. This system achieves nearly perfect conversion of monomers to polymers with high-resolution patterning and improved mechanical strength.
Photopolymerization is a widely used technique in various industries, including 3D printing, dentistry, and microelectronics, where liquid monomers are converted into solid polymers upon exposure to light. The process of generating free radical species – reactive intermediates crucial for initiating polymerization – typically relies on ultraviolet (UV) light, which can be harmful and requires specialized equipment.
However, the new study presents an alternative approach using visible light, which is safer and compatible with a wider range of materials. The team capitalized on the unique features of transition metal complexes, specifically iron complexes, which can undergo light-induced ligand-to-metal charge transfer (LMCT) transitions. These transitions generate reactive radical species through the transfer of an electron from the ligand to the metal center, initiating polymerization.
By combining an iron complex with a carefully designed visible light absorber, the researchers achieved highly efficient visible light-induced free radical photopolymerization. The absorber serves as a photosensitizer, capturing visible light and transferring energy to the iron complex, which then generates radical species.
Furthermore, the team successfully applied their system in various practical applications, including 3D printing with sub-100-micrometer resolution, dental composite curing, and fabrication of soft actuators and sensors. The improved mechanical properties and biocompatibility of the resulting polymers make them well-suited for these applications.
The study's corresponding author, Craig J. Hawker, Professor of Chemistry and Materials at UC Santa Barbara, highlights the significance of their findings:
"The ability to use visible light for efficient free radical photopolymerization opens up new opportunities in many areas, including 3D printing, coatings, and biomedical applications. This work represents a major advance in the field of photopolymerization and has the potential to revolutionize how we process and manufacture materials."
By integrating visible light-absorbing molecules into photopolymerizable systems, the researchers effectively enhance the efficiency of free radical photopolymerization, paving the way for more versatile, safer, and practical applications in various industries.
