Scalable Fabrication of Thick Opals through Drop-Casting Concentrated Suspensions with In-Solution Ordering

Self-assembled materials, studied for optical, mechanical, and fluidic applications, have not yet been widely adopted due to slow manufacturing times. We demonstrate a drop-casting process that provides a rapid approach to fabricate large and thick opals from 40 to 55% w/v solutions of charged polystyrene particles. The high concentration allows for rapid drying, leading to fast assembly times, and the charged particles repel in solution and partially order prior to evaporation. Cryo-FIB SEM images of frozen solutions combined with inverse opals fabricated from still-wet templates visualize the particle ordering prior to assembly. This method produces well-ordered opals with areas of 6.25-100 cm² and thickness of 100-150 μm, which take 0.5-1.25 h to assemble. In addition, the procedure enables continuous fabrication using a doctor blade to spread the material across the substrate. We demonstrate feasible and scalable opal and inverse opal fabrication.