Photothermal synergy mechanism in near-infrared photopolymerization for 3D printing acceleration and mechanical enhancement

The efficiency of near-infrared (NIR) light-induced photopolymerization depends considerably on its photodynamics, which is affected by photoinitiated systems and, inevitably, the thermal effect of NIR light. This study reports the underlying photothermal synergy mechanism of NIR light-induced up-conversion material-assisted photopolymerization (UCAP) employing extra thermal initiation for utilizing undeveloped heat to improve NIR photopolymerization and 3D printing efficiency. The results revealed that excited up-conversion particles (UCPs) not only provide upconverted photon energy but also release heat to aggravate the thermal effect after NIR irradiation. The designed photothermal synergetic curing (PTSC) systems recycle unavailable heat to reduce the necessary energy threshold of the UCAP process by 35% and accelerate NIR photopolymerization for rapid 3D printing of complex structures with 40% enhanced mechanical properties. Moreover, oxygen inhibition is alleviated to improve the surface sharpness of printing materials due to the utilization enhancement of NIR light energy to increase, particularly, the overall surface conversion. The established photothermal synergy mechanism in UCAP provides a theoretical foundation for efficiently fabricating various unsupported and sharp-surface materials, highlighting the potential applications of UCAP technology in high-precision material manufacturing. A photothermal synergy mechanism for recycling unavailable heat to improve light energy utilization and reduce the cured threshold during NIR photopolymerization to improve 3D printing efficiency based on UCAP.