Controlling photochemical reactions with precise spatial-temporal control is at the heart of engineering high-resolution, functionally-graded materials, with targeted properties ranging from stimuli-responsiveness to morphology tunability. While additive manufacturing has risen as a powerful platform in using light to pattern architecturally-complex materials, limitation exists in achieving large-area patterning with high resolution. Herein a dual-wavelength digital-light-projection (DLP) system has been developed with low resolution and minimal control in the rate and the location of specific photochemical reactions. In this work, a dual-wavelength laser system in combination with projection systems controlled by digital-micro-mirrors was developed to achieve sub-diffraction limited, wavelength-specific photochemical reactions for 3D printing purposes with higher resolution and the potential of accessing multi-material patterning. To understand the wavelength-specific photochemistry and to characterize the boundary at which the two wavelengths interact with the reactive resin, we first focused on the diffusion-limited time-scale and the reinitiation. Specifically, we use dual wavelengths (349nm and 445nm) lasers coupled with model reversible addition-fragmentation chain transfer (RAFT) polymerization reaction, with polymerization time scales controlled in the seconds regimes. Here, a co-initiator system (CQ/EDAB) and inhibitor (TETD) systems are employed and two independently controlled laser patterns, generated from 445nm and 349nm wavelengths are projected onto the flow-cell device that selectively activate CQ/EDAB at 445nm and TETD at 349nm. Importantly, polymerization is expected to occur at regimes where only CQ/EDAB are excited, and inhibition to occur at regimes where TETD are simultaneously activated. By controlling the intensity of 349nm light, interdigitated patterns sizes, positions, and gap distances with DMD, the collective excitation and diffusion of CQ/EDAB and TETD radicals are spatially controlled, and their corresponding diffusion dynamics and reinitiation via RAFT polymerization are studied. We found that TETD effectively inhibits photopolymerization of CQ/EDAB and that inhibition length scales are dictated by the radical’s diffusivity when operating in the diffusion-limited time scales (seconds). Moreover, as the power of 349nm light increases, we observed that the reinitiation process involves competition between propagation and inhibition. Furthermore, a radical reaction–kinetics, diffusion model, and reinitiation model were developed to recapitulate our experimental results. Taken together, our work establishes a framework from which fundamental understanding of wavelength-specific photochemical reactions and the reaction-diffusion boundaries of different radicals generated by distinct wavelengths are developed. This knowledge will further impact our next step in studying reaction-limited regimes, where resolution enhancement and arresting of photopolymerization at different morphological states will be explored.
