Magnetic Induction Self-assembly Of Carbon Coated Fe₃O₄ Colloidal Nanoparticles And Its Biomimetic Application

In recent years,it has become a hot topic for scientists to imitate the ordered micro nanostructures in nature and to develop their functions on this basis.As a highly ordered microscopic periodic structure,photonic crystals have attracted wide attention.It can control the light wave and meet the application needs of some special physical optics devices,biological medical diagnosis and chemical sensing.The preparation methods of traditional photonic crystals have many defects,such as long preparation period,low efficiency,expensive equipment,complex process and poor structural stability.Therefore,developing an economical,efficient and large area photonic crystal for photonic band gap in the visible range is very important for expanding the optical performance and application value of photonic crystals.The technology of using the external magnetic field to induce the superparamagnetic colloidal nanoparticles to prepare the photonic crystals by self assembly is gradually developed.Compared with the traditional preparation technology of colloidal photonic crystal,this kind of magnetic-induced self-assembly technology has many advantages.First of all,this technique can complete the construction of the photonic crystal structure instantaneously and realize the variation of the diffraction color from scratch.Secondly,the modulation of the photon structure and its diffraction color only needs to simply change the intensity and direction of the magnetic field and can be easily realized.In addition,a new stimulus responsive functional material with photonic crystal structure can be constructed by introducing the irritation responsive polymer into the photonic crystal structure.The material can convert the information of environmental changes into changes in the detection of optical signals.Therefore,it is bound to play an important role in the scientific research and industrial application of intelligent sensing materials and biomimetic materials.The purpose of this paper is to explore the mechanism of magnetic induced self-assembly of magnetic colloidal nanoparticles and the fabrication of photonic crystal materials based on this technique.The microstructure,chemical composition and optical properties of the system are systemically analyzed by a variety of testing methods.The main contents are summarized as follows:Monodisperse carbon coated superparamagnetic Fe₃O₄ colloidal nanocrystalline clusters were synthesized by solvothermal method.The colloidal nanoparticles have core-shell structure,the core is formed of superparamagnetic Fe₃O₄ magnetic crystal cluster,the negative charge on the surface of the carbon shell endow good dispersion in the solution with the particle.Under the induction of external magnetic field,the nanoparticle can self assemble in the solution system to grow the ordered one dimensional photonic crystal structure with several microns,and show strong diffraction color.This phenomenon is the result of the joint effect of the magnetic packing force produced by the external magnetic field and the electrostatic repulsion provided by the negative charge on the surface of the nanoparticles.In addition,the nanoparticles have good stability and have good magnetic assembly performance even after three months of preservation.Induced self-assembly technology and free radical polymerization using magnetic structure,one-dimensional photonic crystal immobilized in poly（isopropylacrylamide-co-acrylamide）glycol gel matrix to prepare a highly stable,visually display the self pressure,humidity,ion responsive hydrogel photonic crystals film.The whole preparation process is simple,time consuming and the color shape of the photonic crystal film can be made arbitrarily.The photonic crystal film has obvious color change when the external pressure changes.It has super fast pressure response ability.The diffraction wavelength range is 260 nm.It has high sensitivity and achieves some image display.When the relative humidity changes from 11%to97%,the color of the photonic crystal film can be converted from green to orange red,and the diffraction wavelength range reaches 190 nm.In the range of ion concentration of 1500 m M-2850 m M,the variation of the peak of the diffraction spectrum of the 130 nm is accompanied and the color change can be detected by naked eye.Furthermore,the cyclic test shows that the photonic crystal film has good stability and repeatability on the optical signal.In addition,it can also be used as an environment-friendly photonic writing board.It can be wrote with distilled water as ink and removes imprints in dry air to achieve multiple reusing.This low-cost,non power consumption photonic crystal film can also achieve quantitative detection of pressure,humidity and ion concentration similar to pH test paper,which is of great significance for the future industrial production.