Preparation And Application Of Shape Memory Photonic Crystals With Bistable Order-disorder Structures

Photonic crystals,as periodic dielectric structures with photonic stopbands,can manipulate the flow of light and has attracted tremendous interests.For commonly adjustable photonic crystals,however,the temporarily configured nanostructures and optical states cannot be memorized once the external stimuli are ceased.Compared with conventional photonic crystals with fixed photonic stopbands,reconfigurable photonic crystals that can change and recover their optical property in response to external stimuli.Shape memory polymers,which can memorize temporary shape and revert to their permanent shape upon exposure to an external stimulus,are thought as ideal materials to construct reconfigurable photonic crystals with optical bistability.Silica microspheres were self-assembled into 3D photonic crystals as templates by vertical assembly method.In this study,we present the reconfigurable inverse opal photonic crystal membranes with optically bistable states,which were enabled by "cold" programming at room temperature and heating or solvent-recoverable shape memory polymers.The reversible transition of photonic crystals between an ordered permanent state and a disordered temporary state during the cyclical programming and recovery results in a mutation in appearance and photonic photonic band gap?PBG?,and the states can remain after external stimuli are removed.First,thermal response shape memory photonic crystals were built with polyethylene glycol diacrylate?PEGDA?and ethoxylated trimethylolpropane triacrylate?ETPTA?copolymer?ratio 4:1?.The photonic crystals showed no Bragg diffraction peaks after dying out of water at room temperature,while orderly structures fully recovered around 2.5 s at 80 oC.Due to 640 nm displacement of PBG and 65% light transmittance difference value,the photonic crystals have a good application prospect in a rewritable optical switch.Second,solvent response shape memory photonic crystals were built with polyethylene glycol diacrylate?PEGDA?and polyurethane acrylate?PUA?copolymer?ratio 1:5?.The photonic crystals showed no Bragg diffraction peaks under 1.25 MPa pressure at room temperature,while orderly structures fully recovered after dying out of acetone.Due to good resolution,optical reversibility and stability,the photonic crystals can be used as a rewritable optical data storage medium.Finally,light response shape memory photonic crystals were built with 0.2% mass fraction of Cu₂ S doped polyethylene glycol diacrylate?PEGDA?and polyurethane acrylate?PUA?copolymer?ratio 1:5?.The photonic crystals showed no Bragg diffraction peaks after dying out of water and alcohol?volume ratio 1:1?at room temperature,while orderly structure fully recovered around 2.6 s at 980 nm laser irradiation?power density of 7.5 W/cm2?.Due to high reversibility and optical stability,the photonic crystals can be used in laser direct writing reusable equipment.