Tuning the refractive index of homopolymer blends by controlling nanoscale domain size via RIR-MAPLE deposition


Anti-reflection (AR) coatings designed for glass and other rigid, inorganic substrates are commercially available; however, these inorganic AR coatings tend to crack or delaminate on flexible substrates. A polymeric film with a gradient refractive index (GRIN) profile would make an ideal AR coating for flexible substrates, but such coatings are challenging to fabricate using traditional, solution-based techniques. Emulsion-based resonant infrared, matrix-assisted pulsed laser evaporation (RIR-MAPLE) offers a straightforward approach to enabling the desired GRIN profile in polymeric materials. Two homopolymers (polystyrene (PS) and poly(methyl methacrylate) (PMMA)) are deposited as a blend and one component (PMMA) is dissolved, leaving behind a porous PS film. The porosity and refractive index (RI) are controlled by the volume ratio of the two homopolymers in the film. Structural and optical characterizations, as well as comparison to modeled optical properties, confirm that porous films fabricated from polymer blends deposited by RIR-MAPLE behave as effective media over most of the visible spectrum. While evidence for the partial collapse of the porous polymer networks is observed, the RI of the porous films is reduced from that of the bulk material. Importantly, these studies demonstrate that RIR-MAPLE should enable broadband, omnidirectional, polymeric AR coatings appropriate for flexible substrates. Nanoporous homopolymer thin films deposited by resonant infrared, matrix-assisted pulsed laser evaporation (RIR-MAPLE) for use as effective media in anti-reflection coatings are presented. Current anti-reflection technologies are available for inorganic substrates, but tend to crack and delaminate on organic substrates. Films of two homopolymers co-deposited by RIR-MAPLE, after removal of one component, demonstrate nanoscale domain sizes suitable for refractive index tuning across the visible spectrum. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.