Modeling Strategy for 3-Wavelength (UV, Blue, Red) Controlled Photopolymerization: Part-II, Improved Conversion and Confinement in 3D-Printing

Abstract

Detailed kinetics for a 3-wavelength photopolymerization confinement (PC) system is presented for both numerical solutions and analytic formulas. The dynamic profiles are simulated for oxygen, free radical, and conversion for various situations of: blue-light only, 2-light (red and UV), and 3-light (red, blue, UV). An effective PC requires two conditions: (i) a strong N-inhibition for uncured regime with a low conversion (triggered by the UV-light); and (ii) a weak S-inhibition (oxygen-induced) for high conversion under the blue-light or blue and red-light initiation. Good PC candidates are governed by collective factors of: (i) the double ratio of light-intensity and initiator-concentration, (ii) monomers rate-constant; and (iii) effective absorption constants at specific wavelength and initiators. A new reverse feature for the role of N-inhibition on the blue-conversion is found. 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, having a pre-irradiation time TP=200 s for red-light only, and reduced to 150 s, when both red and blue-light. System under UV-only leads 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: (a) high conversion of blue-light (without UV-light), enhanced by red-light pre-irradiation for minimal S-inhibition; and (b) efficient PC initiated by UV-light produced N-inhibition for reduced confinement thickness and for high print speed.

Unified Theory for Hybrid-Photocatalysts: A Review on New Strategies for Synergic, Enhanced Conversion Efficacy and Photoredox Cycle

“…As reported by van der Laan et al [4], the effectiveness of a photoinhibitor in a two-color system is strongly monomer-dependent, which also requires: (i) a high conversion of bluephotoinitiation in the absence of the UV-active inhibitor; (ii) a strong chain termination with significant reduction of blue and UV conversion in the presence of UV-active inhibitor and (iii) short induction time or rapid elimination of the inhibitor species in the dark (or absence of UVlight) [22]. Synergic effects have been reported using co-initiator and/or additives and 2-and 3wavelength systems [8,10]. Conversion efficiency may be also improved by reduction of the oxygen inhibition effect [23].…”

“…many of our theoretically predicted features remain to be explored and confirmed experimentally, including the following new directions/topics: (i) optimal conditions [26][27][28] of the key parameter P=bIC0 for maximum convesion efficacy (CE); (ii) transient and steady-state dependence of CE on the parameter P, which are in general given by a scaling law of P m , where m = 0.5 to 1.5, depending on various conditins as discuused in the present articles, Eq. (11) to ( 15); (iii) tehe competing features between FRP and CP, and their dependence on the concentartion ratios, such as [A][B]/[C]; (iv) available high efficacy under a minimum dose and/or initiator concentration, for safty issues; (v) enhancements via various strategies of reduction of oxygen inhibition effects, or production of extra radicals; (vi) methods for maximum initiator regeneration (RGE), such that catalytic cyle is available under minimum initiator concentration; (vi) new materials or functional groups for absorption in the visible to near IR range for thick polymers; and (vii) multi-wavelength system for orthogonal type excitation, which is critical in 3D printing, speed and resolutions [7,8] We have presented comprehensive model for various systems of G1/ Iod/EDB, and BC/Iod/EPOX systems based on the proposed mechanism of Rahal [17], Bonardi {20], Tar et al [20], and Mau [24]. Analytic formulas are developed to explore the new features including: (i) efficacy of FRP is an increasing function of the light intensity (I), the effective absorption coefficient (b), and the concentration sum of A0(k1B0 + 2k2E0), for transient state.…”

“…The present comprehensive model (with minimum mathematics) will focus on the enhancement mechanisms/pathways, provides analytic formulas which can be used to analyze reported data, and, more importantly, serves as guidance for exploring new functional materials or new kinetic schemes for improved conversion or procedures in applications such as additive manufacturing (AM), 3D and 4D bioprinting. The present article will skip most of the detailed derivations of the formulas with an emphasis on the synergic and enhancement schemes, whereas more complex kinetics with detailed mathematical approaches, may refer to the modeling published by Lin et al [7][8][9][10][11]17,23]. Furthermore, a greater details on the schemes of various systems can be found in Lin et al [25].…”

Efficacy Modeling of New Multi-Functional Benzophenone-Based System for Free-Radical/Cationic Hybrid Photopolymerization Using 405 nm LED

“…Light sources in UV (365 nm) has been conventionally widely, whereas light sources in near-UV (400-410 nm) and visible (430 to 680 nm) and near infrared (700 to 1064 nm) have been explored more recently in various applications such as additive manufacturing (AM), 3D and 4D bioprinting [3,4]. Both spatial and temporal controlled 3D processes were reported using single and multiple wavelength lights [7][8][9][10][11].…”

“…In comparison, FRP-radicals (R and S) are produced by the (positive) k2T[E] term in Eq. ( 7) and (8). Therefore, higher concentration of [E] will enhance the CE of FRP, but it also supresses the CE of CP, a competing effect.…”