Nanostructured Polymer Films Exhibiting Solvent-Responsive Photonic Band Gaps

Tunable and reversible photonic band gap materials generated from nanostructured block polymers have shown applications in displays, sensors and waveguides. Here, we present a way to rationally design the change in the photonic band gap of a lamellar-forming poly(1,2-butadiene)-block-poly(ethylene oxide) (1,2PBD-b-PEO) on the addition of solvents that are able to selectively swell one or both domains. A good solvent for both 1,2PBD and PEO domains, like tetrahydrofuran, leads to the largest increase in the domain spacing, and as a result, the largest change in the photonic band gap. For selective solvents like water and hexane, only one domain swells (PEO or 1,2PBD domain, respectively), leading to smaller changes in the photonic band gap. Cryogenic scanning electron microscopy and small-angle X-ray scattering were used to characterize the structural changes that occur on addition of the different solvents, while optical reflection measurements were used to determine the change in the photonic band gap. The work presented here highlights the necessary parameters for tuning the photonic band gap properties for block polymer materials using the combination of solvent quality (e.g., degree of polymer domain swelling) and changes in the refractive index.