Self-assembled polymeric solid films with temperature-induced large and reversible photonic-bandgap switching.

In aqueous solutions the response of polymers and biological matter to external conditions, such as temperature and pH, is typically based on the hydrophobic/hydrophilic balance and its effects on the polymer conformation. In the solid state, related concepts using competing interactions could allow novel functions. In this work we demonstrate that polymeric self-assembly, reversibility of hydrogen bonding, and polymer-additive phase behaviour allow temperature response in the solid state with large and reversible switching of an optical bandgap. A complex of polystyrene-block-poly(4-vinylpyridinium methanesulphonate) and 3-n-pentadecylphenol leads to the supramolecular comb-shaped architecture with a particularly long lamellar period. The sample is green at room temperature, as an incomplete photonic bandgap due to a dielectric reflector is formed. On heating, hydrogen bonds are broken and 3-n-pentadecylphenol additionally becomes soluble in polystyrene, leading to a sharp and reversible transition at approximately 125 degrees C to uncoloured material due to collapse of the long period. This encourages further developments, for example, for functional coatings or sensors in the solid state.