Steric-Repulsion-Based Monodisperse Superparamagnetic Nanoparticles And Responsive Photonic Crystals

One dimensional magnetic responsive photonic crystals have the merits of fast response,wide and reversible tunable color range and high color saturation.They are composed of nanocrystal cluster particles with high loading of magnetic contents,superparamagnetism and strong electrostatic repulsion force.However,they have no other responsiveness other than magnetic field.What's more,they are dynamic one dimensional periodic structures of unconnected magnetic particles which could only exist in the solutions and very fragile to perturbations.Therefore,it is vital to immobilize those structures in different matrix with diverse functionalities.Unluckily,the periodicity of traditional electrostatic-repulsion-based magnetic responsive photonic crystals are easily deteriorated by ionic species or impurity in the solutions resulting in limited choices of solid functional matrix.In this dissertation,we developed a new kind of magnetic responsive photonic crystals which relies on steric repulsion force instead of the electrostatic force to construct the one dimensional periodic structures.It largely increases the properties of the original materials and also developed new applications.The main research contents are as follows:1.By taking iron?III?chloride hexahydrate as the source for Fe₃O₄,monodisperse superparamagnetic particles are fabricated by a modified polyol process in the presence of polyhydroxy compound?glucose or tannic acid?and poly?vinyl pyrrolidone??PVP?.The formation mechanism is:glucose derivatives constrain the growth of primary grains in the particles,the size of which account for the superparamagnetism of the as-obtained products,while PVP molecules prevent the random agglomeration of the primary grains which facilitate the formation of monodisperse particles.Those superparamagnetic CNC particles show a long-range steric repulsion sufficiently strong enough to counteract the magnetic attractive force which finally constructed steric-repulsion-stabilized MRPCs.They cannot only manifest color tunability within nearly the entire visible spectrum in solvents of diverse polarities,but also insusceptible to the variation of ionic strength or pH value.These merits enable the solidification of the one-dimensional ordered magnetic photonic crystalline structures in a wide range of organic polymers promising lots of potential applications.2.Because of the distinct advantages of steric-repulsion-stabilized MRPCs,we use them for the improvement of the properties of current responsive photonic crystal film or microballs based on colloidal self-assembled structures.First,in order to solve the problem that the traditional pH responsive films always rely on post-treatment for the acquirement of functional ionic groups,we first fabricated a pH responsive film based on MRPCs by a simple radical polymerization.Since the dynamic 1D structures are not susceptible to ionic monomers and initiator,ionic monomers can be freely used.The as-obtained film possess wide tunable color range even in high ionic strength which is 6⁸ times better than their previous counterparts.On the other hand,for the existing RPC balls based on 3-D photonic crystals,they have suffered from color unevenness for visualization owing to the curvature of periodical structures.We have demonstrated magnetically switchable,thermal and solvent RPC balls based on1-D magnetic photonic crystals.The homogeneous distribution and collective orientation of 1-D periodical nanostructures in the responsive polymer insure the color uniformity of RPC balls.What's more,the as-prepared photonic balls have a uniform volume change during the color changing process to external stimuli which promises their free rotation between 0°and 90°to realize“on”and“off”states for the demonstration of structure colors.3.Traditional responsive hydrogels based on photonic crystals always adopt the form of film and microball for the realization of different functionalities.However,because all the one dimensional periodical structures of magnetic photonic crystals are collectively immobilized in film or microball,they normally have large dimensions.Hence,they are hard for miniaturization and possess low resolution and sluggish responsiveness which account for their incapability for microenvironment sensing and imaging along with real-time on-line monitoring.Here we have for the first time demonstrated a new category of hydrogel-based PC sensors?responsive photonic nanochain probes which are at least 2³ orders of magnitude smaller than the previous counterparts.Each probe is obtained by immobilization of the smallest periodic structure of magnetic responsive PCs,which is composed by linear aligned magnetic particles,in hydrogel to form a peapod-like chain.A series of responsive photonic nanochain probes?including pH,solvent and temperature-responsive?can be fabricated in a large-scale by a general hydrogen bond-guided template polymerization method.Taking pH-responsive hydrogel-based photonic nanochains for example,they not only validating the feasibility of using structural colors for microenvironment sensing and imaging,but also manifest higher resolution and faster response time by 2³ orders of magnitude than the previous ones due to the submicrometer size.