| Ordered Nanostructures give beautiful colors to the nature and have some unique properties. They are made to be provided with potential applications at magnetic storage, catalyze, optical communications, laser devices and 3D artificial neural networks.There are many good variety of method to prepare ordered nano-arrays, among various methods, self-assembled colloidal particles is of special interest as it provides the possibility to modify its properties and functionality by external stimuli (electric, magnetic fields, light, etc.). The preparation process has certain controllability and purpose. In the formation process of an ordered nano-structured film, the interaction between nanoparticles can be controlled by changing the surface properties of particles, the surrounding solvent environment and other external conditions. In this way, people can build the ordered nano-structured films followed their own wishes. The research on the interaction between nanoparticles which was studied through the method of magnetochromic colloids mechanism can be important for guiding the preparation and synthesis of ordered nano-assemblies.The superparamagnetic Nano-Fe3O4 particles were selected as studied object for this paper. As a functional material, Fe3O4 show many special features in magnetic recording materials, special catalyst materials, basic materials of magnetic fluid, assembly units of ordered nano-array, magnetic pigments, drugs, etc.Superparamagnetic Fe3O4 nanoparticles with well-controlled size and high water solubility were produced through the method of high-temperature hydrolysis reaction. The size of the nanocrystals can be precisely controlled from 30nm to 180nm by sismply changing the amount of NaOH while keeping all other parameters fixed. The sample was dispersed in water forming its hydrosol after it was cleaned. One appropriate external magnetic field was applied, magnetochromic colloids appear. Because Nano-FesO4 particles which were dissolved in water will form a regular arrangement in the coulomb force and magnetic force. Magnetochromic colloids will appear when the distance between the layers of ordered structures can be comparabled to the visible light and satisfy the Bragg diffraction formula. The diffraction peak wavelength over the entire visible spectrum can be tuned by changing the magnetic field strength.The diffraction was not only influenced by the external magnetic field strength but also the sample particle size, pH value, concentration, aging time, etc.1) Magnetochromic colloids blue-shift with the increase of the particle size.2) The diffraction peak blue-shift with the decrease of the pH value. This has a great relationship with the ionization of polyacrylic acid (PAA) band to Nano-Fe3O4 particles surface. The diffraction peaks red-shift firstly and then blue-shift with the decrease of concentration in the same magnetic field. This is also affected by the ionization of PAA in the water. The ionization of PAA changes the conductivity of the Nano-Fe3O4 particles'hydrosol.3) The diffraction peaks blue-shift with its aging time. Because the samples placed in air will absorb CO2 to form carbonic acid. The fragmentation of Nano-Fe3O4 clusters is also a reason for it.
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