Precise Control of Mesoscale Morphology in Photoreactive Polymer Blends Using Visible Light Beams

Controlling the structure of polymeric blends with microscale precision and high scalability is critical for their deployment in applications. We present a new process to organize multiphase morphology in photoreactive polymer blends by coupling light-induced polymer waveguide formation to polymerization-induced phase separation. By exposing a blend of photocrosslinker and linear chain polymer to an array of microscale beams, generated from a visible-light LED or white-light source, photopolymer fibers grow from the point of exposure across the blend medium. Concurrently, the underlying polymerization of the growing fibers induces spatially-local, mesoscale spinodal decomposition of the blend along the fibers’ path lengths. Thereby, large-scale, multiphase morphology is produced that corresponds to the beams’ size and arrangement. We show that polymer blend morphology can be controlled with microscale precision over unprecedentedly large depths (> 1 mm) and areas (> 10 cm²) – well beyond the limits of uniform polymerization and holography – by varying the size and arrangement of the beams. Systematic variation of the relative weight fractions in the blend also tunes the final structure. While a single array of beams produces a 2D structure, 3D structures can be produced by propagating multiple arrays in different directions through a common surface of the medium. The generalizable nature of phase separation enables a wide range of polymer blend and hybrid blend systems to be self-organized. Hence, we anticipate that this method will become a versatile mechanism that serves the dual role of fabricating 2D and 3D mesostructured composite materials, while concurrently organizing the morphology of its components.