Research On The Fabrication Of Stimuli-Responsive Structural Colors Based On Femtosecond Laser Two-Photon Polymerization And Their Applications

The study of structural colors(SCs)originated from bionics,but the horizon of mankind is not stuck in the wings of butterflies or the feathers of peacocks.Since the formation of SCs is directly related to the morphology and structural parameters,any variance of morphology and feature size will lead to the sudden change of SCs.And SCs based on grating diffraction will change as the angle of incident light varies.From these perspectives,SCs hold infinite potential in optical sensing.Stimuli-responsive material can respond to external stimuli,such as the change of structure size or the property of material.SCs based on stimuli-responsive material can realize the change of color when exposed to external stimuli.At the same time,researchers are trying to promote the miniaturization of SCs with an aim to improve the density of structural color pixels.Femtosecond Laser Two-Photon Polymerization(fs-TPP),however,can achieve processing resolution up to-100 nm,and holds much higher degree of freedom compared with other precision manufacturing techniques,for example,Electron Beam Lithography(EBL)and Ion Beam Lithography(IBL).In this dissertation,we polymerized stimuli-responsive material(SZ2080 photoresist and pH-responsive hydrogels)to fabricate woodpile SCs based on fs-TPP,and achieved the encryption and decryption of structure color patterns based on the stimuli-responsive property of polymerized materials(surrounding mediums and the pH in solution).The content of this work can be divided into following three parts:(1).The SZ2080 woodpile SCs were realized based on fs-TPP,and the encryption and decryption of structure color patterns was achieved based on SZ2080 photoresist’s affinity to organic solvent.Firstly,the resolution of SZ2080 was tested.Then,we designed four-layer Woodpile Structures(WSs)on a pillar so that they can expand in a freeform manner and acquired their expansion ratio in different mediums afterward.Based on the above-mentioned results,we fabricated SZ2080 woodpile SCs,and achieved their color changing in different mediums.Finally,we realized the encryption and decryption of structural color patterns based on the similarity of SCs with different structural parameters in deionized water(DI water)and air when fabricated with rather low laser power.(2).Aiming at the problem that the critical pH value of existing pH-responsive hydrogels is either acidic or alkaline,a new solvent-free pH-responsive hydrogel formula was developed,and the composition was carefully chosen through comparative tests,so that this new hydrogel demonstrated terrific pH-responsive speed(480 ms),close-to-neutral critical pH value and excellent biological compatibility.After that,the 4D printing of hydrogel woodpile SCs was realized,and processing resolution up to 98 nm was observed.Then,we systematically investigated the influence of laser power and structural parameters on hydrogel SCs.In the end,reversible encryption and decryption of structural color patterns by adjusting the pH of environment was accomplished.(3).Based on FDTD simulation,the mechanism of the emergence of SCs was further explored.By comparing theoretical simulation and experimental spectra,we concluded that the emergence of SCs was mainly based on the interference and diffraction of WSs,which is quite similar to the stacking two-dimensional gratings,and their color changing could be attributed to the change of structural parameters.The color changing of SZ2080 SCs in DI water or air is because of their shrinkage,so light propagating through is reduced,resulting in the overall dropping of transmittance.The color change of hydrogel SCs,however,is mainly due to the drastic change of structural parameters cause by pH response.