Photo-polymerization using quantum dots for stable epoxy coatings†

Photo-polymerization is at the foundation of many industries such as dentistry, coatings, adhesives, and stereolithography 3D printing. However, the organic cationic photo-initiators currently used are toxic, expensive, and difficult to tune with respect to the wavelength of light required to initiate polymerization reactions. For example, current stereolithography 3D printing resins are unstable under sunlight. Here, we demonstrate that less expensive and non-toxic titania quantum dots made via the scalable flame spray pyrolysis technology can photo-polymerize epoxy when exposed to UVC (not present in sunlight on Earth), while being insensitive to UVA (present in natural sunlight on Earth) leading to resins that are photo-stable during end use. We use NMR and FTIR to demonstrate that photo-polymerization is catalyzed under UVC but not UVA, and nanoindentation to monitor the mechanical stability of epoxy films during post-polymerization UVA exposure. This approach allows precise control over the wavelengths of light under which photo-polymerization can and cannot occur, and is also transferable to other photo-catalytic reactions.

Keywords: Polymers; Photo-polymerization; Catalysis; Quantum dots; Nanotechnology.