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A team of scientists from the Hebrew University of Jerusalem led by Professor Shlomo Magdassi has developed insoluble photoinitiators made from composite nanoparticles that increase the efficiency of photopolymer 3D printing.
Shlomo Magdassi should be familiar to our readers from Nano Dimension, which developed the DragonFly 2020 3D inkjet printer. DragonFly 2020 uses a variety of nano-inks created by Professor Magdassi and his colleagues as consumables. This time, the team presented a new solution for SLA / DLP printing using aqueous solutions, and even with increased energy efficiency and speed. The new technique does not require the use of toxic solvents, making the process attractive for applications in biomedical research. In addition, the new photoinitiators absorb ultraviolet radiation about 300 times more efficiently than the best commercially available water-soluble counterparts.
“Photopolymerization requires photoinitiators that break down into free radicals when exposed to light. We report on a new group of photoinitiators for 3D printing based on hybrid semiconductor-metal nanoparticles. Unlike conventional photoinitiators, which degrade when exposed to radiation, these particles form free radicals through a photocatalytic process. The absorption of light by semiconductor sections of the nanorods is accompanied by charge separation and the transfer of electrons to the metal tips, which allows the formation of radicals during redox reactions under aerobic conditions, ”the researchers write.
In other words, instead of converting common photoinitiators into high-energy oxygen molecules, the free radicals needed to form polymer chains, the charge is transferred to the oxygen in the water. In this case, the very decrease in the oxygen content in water as the molecules are integrated into the polymer chains contributes to more efficient polymerization. An additional advantage, scientists believe, is the relatively high cross-section of nanoparticles, which plays into the hands in two-photon polymerization processes and makes it possible to effectively use such photoinitiators for printing submicron structures at high resolution.
"The semiconductor and metal segments of nanoparticles can be altered in terms of composition, size, shape and relative position for optimal efficiency in photopolymerization processes, including 3D printing," the researchers point out. In particular, it is possible to choose the wavelength of the absorbed radiation by adjusting the band gap, and also to use different coatings for use in solutions with different chemical compositions.