Investigation Of Responsive Photonic Crystals Based On Butterfly Wing

Responsive photonic crystal(PC)would exhibit reversible changes in reflectance wavelength under external stimuli.Generally,external stimuli are applied,which would result in the variation of photonic band gap.In other word,responsive PC can transform such as chemical,mechanical signal to optical signal,which attracts many researchers to study about these novel materials.Artificial photonic crystals have been well prepared by selfassembly,spin coating and other ways.However,there lacks a simple,lowcost approach to the fabrication of high-performance responsive PCs with more precise structures.We herein developed a new kind of responsive photonic crystals(PCs)by utilizing butterfly wing as the template,which has photonic structures.As a natural PC,readily accessible butterfly wings have brilliant colors due to their unique hierarchical structure.From our perspectives,the combination of this biological PC structure with smart polymers would demonstrate novel or highly improved properties and thus lead to a wide range of new applications.The main performances we achieved were as follows:(1)Firstly,Papilio paris wings having hierarchical,lamellar structure were chosen as the template.A coating of poly(acrylic acid)and poly(acrylamide(AAm))was carried out on the surface of wing scales via in situ copolymerization method.The resultant PCs exhibited high performance of color tunability to environmental pH,as detected by reflectance spectra and visual observation.The introduction of AAm into the system created covalent bonding which robustly bridged the polymer with the wings,leading to an accurate yet broad variation of reflection wavelength to gauge environmental pH.The reflection wavelength can be tailored by the refractive index of the lamellar interspacing due to the swelling/deswelling of the polymer.The mechanism is not only supported by experiment but proved by finite-difference time-domain simulation.It is worth noting that the covalent bonding has provided the PCs-based pH sensor with high cycling performance,implying great potential in practical applications.(2)Secondly,an optical induced thermo-responsive PC was fabricated by coating Papilio paris with thermo-sensitive poly(N-isopropylacrylamide)(PNIPAm)with nanoparticles Ag formed in situ.As an optic-thermo converter,Ag nanoparticles can convert light into thermal energy because of its surface Plasmon resonance properties.The increase of temperature results in the phase transition of PNIPAm coating on the wing scales,leading to the change of the bioinspired PC structure.Correspondingly,a blue shift in reflectance wavelength was detected for the obtained PC.Interestingly,a reversible optical thermos-responsive performance was observed through controlling the light source.