Investigating phase separation and structural coloration of self-assembled ternary polymer thin films

Poly(3-hexylthiophene-2,5-diyl) (P3HT) can generate nanoporous structures with variable pore diameters ranging from 150 to 600 nm from spin-coated blends with polystyrene (PS). In the present study, we observe the effect of the addition of polymethylmethacrylate (PMMA) to P3HT:PS blends to increase the pore-to-pore dimensions up to the micrometer scale. The phase separation in the ternary blend can be directly visualized by replacing the commercial (non-emissive) PS with a boron-dipyrromethene functionalized PS to distinctively locate the red-emitting P3HT and the green-emitting PS phases. In particular, in the ternary blend with high PMMA contents, we observe that PS acts as a compatibilizing agent at the interface between the P3HT and PMMA phases. After selective removal of the PS and PMMA phases using acetone, we demonstrate that, in these P3HT structured thin films, iridescence can be observed as they exhibit angle dependent reflectivity which is further emphasized when covered with a thin metal layer. The metal covered nanostructured P3HT films display bright color switching properties with blue and red emission at low and high reflection angles, respectively. Published by AIP Publishing.