Construction Of Stimuli-responsive Photonic Crystals And The Exploration Of Color Changing Mechanism

Due to the tunable structural colors and self-reporting proprieties of stimuli-responsive photonic crystals,they are widely used in the fields of sensing,smart display,anti-counterfeiting,and information encrypting.Composite photonic crystals have attracted much attention because the stimuli-responsiveness could introduced into photonic structures during the fabrication process,but responsive photonic crystals and their structural color regulation mechanism are still rarely used in the fields of smart windows,replication,and multiple information encryption.To expand the application field of composite photonic crystals,near-infrared responsive nanomaterials or various functional groups were introduced into photonic structure during the preparation process.Tunable structural colors of prepared photonic materials were achieved and their color-change mechanism were explored.Reaction solutions were prepared by using gold nanorods,N-isopropylacrylamide,acrylamide and hydroxyethyl methacrylate.After initiated into polystyrene photonic crystal,the reaction solutions were polymerized by ultraviolet light initiation and obtaine near-infrared responsive photonic hydrogels.The transmittance and structural color changes of prepared photonic hydrogels could be adjusting by changing the composition of the reaction solutions.The obtained photonic hydrogel are expected to be used in the fields of smart windows and light-induced rewritable.In order to improve the stability and optical properties of composite photonic materials,inorganic silica based hollow photonic crystals were composited with cellulose acetate to fabricate photonic anti-counterfeiting films.The surface energy of silica was regulated by chemical modification,and realized the regulation of the liquid wetting behavior in photonic crystals,which avoids the structural color disappearance caused by the inner core infiltration.In addition,different groups modified hollow silica photonic crystals showed multi-solvent responsiveness,which broadens the application fields of photonic crystals in organic solvent detection,anti-counterfeiting and multiple information encryption.The main works of this paper are shown as follows:1.To broaden the near infrared responsiveness of photonic crystals,gold nanorods were introduced into N-isopropylacrylamide and acrylamide reaction solution as photothermal converters.Photonic hydrogels were prepared by ultraviolet light induced polymerization after infiltrating into polystyrene photonic crystals（PSPCs）,then the photonic hydrogels were encapsulated by glasses and hot melt adhesive to prepare near-infrared responsive smart windows.The effect of N-isopropylacrylamide amount on transmittance and color change time was investigated,the photonic hydrogel of 90 mol%N-isopropylacrylamide dosage showed a large transmittance change with a transmittance drop of about 90%at 40℃,and the phase transition can be achieved after about 6 s for near infrared radiation or about 30 min for solar radiation.Under the irradiation of near infrared light,the photonic hydrogel can produce a 25nm blue-shift of structural color,and the structural color change showed excellent cycling stability.The passive cooling performance of prepared smart window was also investigated by sunlight irradiation,and the smart window showed 6℃ cooler than ordinary glasses after 60min of sunlight exposure,compared with the same type of this work,the smart window shows better passive cooling performance.2.To solve the problem that the photonic hydrogel cannot be self-supporting and easily becomes opaque,hydroxyethyl methacrylate was selected as polymerized monomer to fabricate another photonic hydrogel.The reaction solution with gold nanorods was infiltrated into PSPCs,self-supporting photonic hydrogels were obtained by ultraviolet induced polymerization.The photonic hydrogel prepared by 70 mol%N-isopropylacrylamide dosage showed the best self-supporting property,its structural color appear a 35 nm blue shift after near infrared irradiation,and the transmittance change was about 30%.Using PSPCs with diameters of 200 nm,225 nm,and 255 nm as templates,the color of the prepared photonic hydrogels can be covered from blue to red.The prepared near-infrared responsive device showed excellent cycle stability and would be useful in the field of the near-infrared light detection and rewritable paper.3.The stability of polymer-based photonic crystals is poor,while the stable silica photonic crystals possessed close refractive index compare to solvents such as water.So,The chemical modification strategy of hollow silica photonic crystals（HSPCs）would expore to avoid the structural color disappearance caused by refractive index matching.Photo-induced Michael addition reaction was used to introduce different modified groups into HSPCs,and invisible patterns were obtained.PS@Si O₂ photonic crystals were calcined at 400℃ for 8 h to obtain the HSPCs with a 51 nm red shift of structural color in response to moisture.The prepared invisible patterns showed good static stability,while the blue pattern can be revealed after human breath.The invisible pattern can response to 25 wt%ethanol aqueous solution and display a green pattern after the background region was modified with halothane,and the invisible patterns showed good cyclic stability.4.Different modified regions could realize variety of wettabilities in response to single solvent,and the acetone solution of cellulose acetate（CA）can be used to prepare self-supporting photonic films in modified HSPCs.To expand the application of HSPCs in the fields of organic solvent detection and composite photonic film fabrication,N-heptanethiol,dodecanethiol and octadecanethiol were introduced into HSPCs to prepare multi-region modified photonic crystals（MMPCs）via photoinduced Michael addition.The Core₂₄₀Shell₁₄,Core₂₄₀Shell₃₀ and Core₂₅₅Shell₅₅ could be used to prepare HSPCs with structural colors varying from blue to yellow.The prepared MMPCs can distinguish organic solvents such as ethylene glycol,n-hexane,cyclohexane and diiodomethane by showing patterns with different shapes and colors with excellent cycling stability.In addition,MMPCs can also be used to construct user-defined stealth patterns,which can display different information for water,5 wt%ethanol and 15 wt%ethanol,respectively.The modified HSPCs could protect inner core from acetone infiltration,and cellulose anti-counterfeiting films with different structural colors and shapes were obtained on the modified HSPCs via CA acetone solution injection printing.This strategy would applied in the fields of complex invisible pattern fabrication and multi-level information encryption,which would expand the design and printing process of photonic anti-counterfeiting patterns.