Rapid fabrication of organic/organic photonic bandgap films with tuneable mechanical properties using blended polymer spheres



In this study, the photonic bandgap (PBG) film with tunable mechanical properties and photonic stop band was prepared by a simple and feasible approach. Colloid polymer spheres with a relatively large diameter (approximate Dn of 200 nm) and different glass transition temperatures (Tg) were blended with small polystyrene (PS) latex (Dn = 20 nm) and were subsequently casted on a substrate for 3 h at 50°C for self-assembly of the PBG film. The monodispersed polymer spheres were synthesized by soap-free emulsion polymerization in the boiling state. The Tg values of the spheres were predetermined based on the Fox equation, and designed to fall in the region of −34°C to 112°C. Small PS could also be synthesized by this approach using the comonomer, sodium p-styrenesulfonate (NaSS), to ensure the small diameter. The long-range ordered structure constructed by embedding the small PS in the PBG film was indirectly confirmed on the basis of SEM analysis, from which the monochromatic film color was determined based on Bragg's diffraction law. Tunable film color was achieved by adjusting the diameter of the spheres, as evaluated using UV–Vis. Tunable mechanical properties of the PBG film were also achieved by varying the Tg of the spheres or the filling ratio of small PS. Based on these approaches, the ultimate tensile strength could be tuned in the region between 0.39 to 4.7 Mpa, and the relative strain could be varied from 1236% to 16%, illustrative of the excellent deformability of the film. Furthermore, by variation of these two parameters, the film properties could be changed from typical elastomer behavior to brittle plastic polymer type behavior, greatly extending the prospective application fields. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 40276.