Preparation And Stimulus Responsiveness Properties Of Gold-doped Photonic Crystal Hydrogel

Photonic crystal materials have wide potential applications in various fields related to color,thanks to their special structural color owing to their unique periodic structure.The combination of photonic crystal structure,stimuli-responsive hydrogel and metal nanoparticles can endow photonic crystal hydrogel with multistimuli responsiveness,which has important application value in the fields of intelligent displays and visibility sensors.In this paper,multistimuli-responsive opal-structured composite hydrogels(OH_PNIPAm/Au)and inverse opal hydrogels(IOH_PNIPAm/Au)were designed and prepared based on the conformational transformation behavior of the thermosensitive hydrogels and the photothermal effect of gold nanorods（Au NRs）.In the first part,poly（styrene-acrylic）（P（St-AA））microspheres with different size were first prepared by the method of soap-free emulsion polymerization.Then,gold nanorods with 808 nm longitudinal surface plasmon absorption peak were prepared by seed-mediated growth method.Finally,Au NRs and P（St-AA）microspheres were assembled to form gold-doped photonic crystal template with three-dimensional opal structure by vertical deposition co-assembly method.This kind of co-assembly method was reliable and simple to fabricate gold-doped P（St-AA）photonic crystal templates with different structural color.The effects of the size,solid content of P（St-AA）microspheres and the content of gold nanorods in the deposition solution on the structural color and integrity of the photonic crystal template were studied in detail.In the second part,the precursor of thermo-sensitive hydrogel poly（N-isopropylacrylamide）was filled into the gap of the gold-doped P（St-AA）photonic crystal template,and then polymerized to form gold-doped opal composite hydrogel(OH_PNIPAm/Au).Xanthan gum was introduced into the OH_PNIPAm/Auto adjust the viscosity of the precursor and played a role in completely preserving the structure of template.The response of the OH_PNIPAm/AAto temperature,near infrared light,p H and mechanical stress were investigated based on the structural color and reflectance spectrum.The results show that the structural color of OH_PNIPAm/AAchanges significantly and the reflection peak shifts significantly under the stimulus of temperature or p H.The structural color of OH_PNIPAm/Auexhibits a blue shift after stretched.Under the irradiation of near-infrared light,the photothermal effect of gold nanorods makes the surface temperature of OH_PNIPAm/Auincrease,and the structural color of OH_PNIPAm/Aualso exhibits a reversible disappearance-appearance near 36℃.In the third part,gold-doped inverse opal hydrogel(IOH_PNIPAm/Au)was prepared by etching away the P（St-AA）photonic crystal template in OH_PNIPAm/Au.The effects of crosslinking degree on the structure and properties of OH_PNIPAm/Auwere explored by adjusting the amount of physical crosslinking point（C-dots）and chemical crosslinking agent.The temperature and photothermal responsiveness of the inverse opal hydrogel were investigated.The results show that IOH_PNIPAm/Auhas three-dimensional ordered macroporous structure.The structural color and reflection peak of IOH_PNIPAm/Auobviously change under the stimulus of temperature or near-infrared light.Therefore,both OH_PNIPAm/Auand IOH_PNIPAm/Auprepared in this work are expected to be used in color sensors or temperature sensing smart windows.