| Responsive photonic crystals are materials that can display color changes in response to environmental stimuli.To date,the most explored responsive optical systems are built by incorporating photonic crystals into stimuli-responsive hydrogels to visually detect humidity,molecules,p H,temperature,solvent,gas,etc.However,the typical bulk optical hydrogels usually show a slow response rate and cannot change their structural color sufficiently fast to respond to external stimuli.In contrast to macroscopic hydrogel,microgels respond quickly to an external stimulus.In this work,a fast and simple method is reported to prepare a freestanding photonic crystal microgel film with multiple responsiveness.Since it is completely composed of microgel spheres,the microgel film has an extremely fast response rate.The main research contents are as follows:The first part is the preparation and characterization of free-standing photonic crystal microgel film with stimulus responsiveness.Different from previous reports,dried amorphous poly(N-isopropylacrylamide-styrene-acrylic acid)(p(NIPAm-st-AA))microgel film was crosslinked to obtain a free-standing photonic crystal microgel film,which doesn’t require to form ordered structures by special treatments,such as long time dialysis,or filtered through special resin.The free-standing microgel film displayed tunable structure color by the swelling/deswelling of the microgels under external stimuli,such as temperature,p H,ionic strength,and organic solvent.Besides,the structural color of the film is angle-independent for the disordered microgel arrays.The second part is the response dynamics and application of the microgel film.The film has ultrafast responsiveness since it is only 10 μm and is completely cross-linked with microgel spheres.The response time for temperature change(from 20℃ to 40℃)was measured only 33 milliseconds,and p H change(from p H 8.3 to p H 2.0)only 2.24 second,much faster than most optical materials reported in previous works.Moreover,programmable color stripes which have the Panther Chameleon’s ability to change skin color are successfully fabricated by patterning microgels with different thermo-responsivity,which exhibited potential applications in biomimetic camouflage.The third part is the preparation and characterization of cross-linked microgel filmhydrogel composite membrane.The prepared microgel films are very fragile even though it has an ultrafast response rate.To overcome this limitation,microgel films have been immobilized in an acrylamide hydrogel matrix.Different from previous reports,in which the position of the microgels was fixed,in our work,the distance between the microgels will change for the intermicrogel crosslinking,the polyacrylamide hydrogels with low cross-linking degrees will not limit the swelling/shrinking of the microgel film.Therefore,the composite film displayed tunable structure color during temperature change.However,the hydrogel without crosslinking microgels has no temperature response,but a good humidity response. |
