Improvement on solvent resistance of photonic crystals by surface modification

In this study polystyrene (PS) spheres were synthesized by emulsifier-free emulsion copolymerization of styrene with methacrylic acid for the fabrication of photonic crystals. A facile method to significantly improve the solvent resistance of photonic crystals was developed through surface modification of PS spheres by poly(vinyl pyrrolidone) (PVP). We used an ethanol soaking test to evaluate the solvent resistance of photonic crystals prepared by pristine, thermal-treatment, and PVP-modification methods. The crystal structure and the absorption band of the photonic crystals before and after the soaking test were investigated. Experimental results revealed that the photonic crystals prepared from the unmodified PS spheres have a very weak resistance to ethanol, resulting in impossibility of carrying out inverse opal photonic crystals. The improvement on solvent resistance by the thermal-treatment method was limited due to the weak bonding or the mergence of PS spheres. We found the photonic crystal prepared from the PVP-modification PS spheres maintains its integrity very well in the ethanol solution after 5-h soaking. Moreover, the photonic crystal and the corresponding inverse opal photonic crystal revealed excellent structure and optical properties.