Preparation Of Photonic Crystals Films Of P(St-Nipam) Core-Shell Nanoparticles And Its Application In Fluorescence Enhancement

Photonic crystals are synthetic crystals, made of two or more kinds of dielectric building blocks. Photonic crystals, with the characteristic of photonic bandgap based on Bragg diffraction, can control the propagation of light whose wavelength is in the range of photonic bandgap in a certain direction. Photonic crystals have wide potential applications in fabricating novel optical devices. With its special properties, photonic crystals can be used in fluorescence enhancement. In this dissertation, monodispersed Poly (styrene-N-isopropylacrylamide)(P(St-NIPAm)) core-shell nanoparticles were prepared by surfactant-free emulsion polymerization method. The as-prepared P(St-NIPAm) nanoparticles were blended with Rhodamine B(RhB), then the photonic crystals films of P(St-NIPAm) embedded with RhB were prepared by simple vertical deposition method, and the effect of the films on the fluorescent enhancement of RhB was studied. The mainly contents and results were as follows:(1) P(St-NIPAm) nanoparticles with different sizes were prepared by one-step surfactant-free emulsion polymerization method using ammonium persulfate as initiator, with a constant molar ratio of monomers. Results indicated that the nanoparticles had an obvious core-shell structure and good monodispersity; There was a linear relationship between nanoparticles sizes and the dosage of the monomers; The mechanism of polymerization of P(St-NIPAm) nanoparticles were compatible with classic homogeneous nucleation theory.(2) The photonic crystals films of P(St-NIPAm) nanoparticles were prepared by simple vertical deposition method. Results indicated that the nanoparticles of the photonic crystals films were in a close-packed face-centered cubic arrangement, and the thicknesses of the films were about8μm, and there were about50layers of P(St-NIPAm) nanoparticles in the films. The stopbands of films were within visible wavelengths, and the measured stopbands were mostly identical to the theoretical calculations, and it had a linear relationship with the size of the nanoparticles. The colors of the films prepared with different size nanoparticles were bluish violet, bluish green, yellow-green and jacinth, respectively.(3) According to the above conclusion and the fluorescence properties of RhB, P(St-NIPAm) nanoparticles whose sizes were280.7,284.1,288.7nm respectively, were prepared with a certain dosage of monomers, and the photonic crystals films of P(St-NIPAm) nanoparticles whose stopbands overlapped either the emission or the excitation wavelengths of RhB by vertical deposition method. The as-prepared P(St-NIPAm) nanoparticles were blended with RhB, then the photonic crystals films of P(St-NIPAm) embedded with RhB were prepared by simple vertical deposition method. Results indicated that when the stopband of the film embedded with RhB overlapped the emission wavelengths of RhB, the fluorescent intensity of RhB was improved, and when the stopband overlapped both the emission and excitation wavelengths, a stronger fluorescent enhancement, nearly doubled, was observed. However, the fluorescent enhancement effect in this dissertation was far weaker than that reported by other researchers, and further research was necessary.