Preparation Of SiO₂/PNIPAm Complex Microgel And Study On Its Self-assembly Behavior

Photonic crystal(PC)is a kind of artificial microstructures periodically arranged by media with different refractive indexes.This highly ordered structure makes the light waves propageate in PC will be regulated by photonic band gap(PBG).When the photonic energy overlaps with PBG,the transmission of photons in PC will be hindered.Based on this mechanism,the stimulus-responsive material can be combined with PC to prepare the stimulus-responsive PC.The stimulus-responsive PC can respond to external stimuli,and convert electrical signals,pressure signals into visible light signals,which greatly expand the application of PC in sensing and detection.In this paper,thermosensitive poly(N-isopropylacryloyl)(PNIPAm)was used as the component material of the PC,the performance and application of the PC were studied,and the main contents are as follows:(1)Firstly,SiO₂microspheres doped with three kinds of organic dyes(Rhodamine B,RhB;fluorescein isothiocyanate,FITC;commercial cationic Fluorescent Yellow,X-10GFF)were prepared and they were used as the cores to synthesize SiO₂/PNIPAm complex microgels doped with organic dyes by free radical polymerization.Then 3D self-assembled colloidal crystals(CCs)of the complex microgels were fabricated by centrifugation.The microstructure of the complex microgel was characterized by Fourier transform infrared(FTIR),transmission electron microscopy(TEM),thermogravimetric(TG),dynamic light scattering(DLS),scanning electron microscopy(SEM)and differential scanning calorimeter(DSC).Moreover,the effect of doping organic dyes and temperature on self-assembly of the microgels were investigated.Manipulation of fluorescence emission for organic dyes by PCs was studied by photoluminescence(PL)and UV-visible spectrophotometer(UV-Vis).The results indicate that,due to the soft and thermosensitive property of PNIPAm shell,continuous adjustment to the PBG of the CCs can be achieved conveniently by varying concentrations of the complex microgels or ambient temperatures,and when PBG of the CCs overlaps with the fluorescence emission peak of the organic dye,fluorescence emission of the organic dye can be manipulated.(2)In this study,using hydroxyethyl methacrylate(HEMA),acrylic acid(AA),and N-isopropylacrylamide(NIPAm)as monomers,two kinds of PNIPAm microgel and HEMA modified poly(N-isopropylacrylamide-acrylic)(P(NIPAm-AA))microgel with similar size were synthesized,through microgel self-assembly,and then the ordered structure was stabilized in situ free radical photopolymerization.The chemical composition and stimulus response of microgels were characterized by Fourier transform infrared(FTIR),differential scanning calorimetry(DSC)and dynamic light scattering(DLS).Moreover,the structure of CC was characterized by scanning electron microscopy(SEM)and ultraviolet visible spectroscopy(UV-Vis).The results indicate that due to the differences in the response of the two microgels to external stimuli,the internal defects of CC can be induced and eliminated conveniently by adjusting the temperature,pH value or sodium ion concentration,and the process is reversible.