Dual- and 3-wavelength Controlled Photopolymerization Confinement for 3D-Printing: Kinetics and Analysis

Abstract

The kinetics and dynamic profiles of monomer conversion for various situations of: blue-light only, 2-light (red and UV), and 3-light (red, blue, UV) are presented. Higher oxygen concentration leads to a lower conversion, which could be enhanced by reducing the S-inhibition via a red or blue light pre-irradiation. The system under UV-only leads to a conversion lower than that of blue-only. However, conversion could be improved by the dual-light (blue and UV), and further enhanced by the pre-irradiation of red-light. The two competing factors, N-inhibition and S-inhibition, could be independently and selectively tailored to achieve: (i) high conversion of blue-light (without UV-light), enhanced by red-light pre-irradiation for minimal S-inhibition; and (ii) efficient PC initiated by UV-light produced N-inhibition for reduced confinement thickness and for high print speed. For a dual-wavelength (UV and blue), the UV-light initiated inhibition effect is strongly monomer-dependent due to different C=C bond rate constants and conversion efficacies. Without the UV-light, for a given blue-light intensity, higher initiator concentration and rate constant lead to higher conversion, Conversion of blue-only are much higher than that of UV-only and UV-blue combined. For example, UV-light controlled methacrylate conversion of a glycidyl dimethacrylate resin is formulated with a tertiary amine co-initiator, and butyl nitrite. The system is subject to a continuous exposure of a blue light, but an on-off exposure of a UV-light. Finally, we developed a theoretical new finding for the criterion of a good material/candidate governed by a double ratio of light-intensity and concentration, [I₂₀C₂₀]/ [I₁₀C₁₀].