Preparation, Characterization And Applications Of Super-paramagnetic Composite Microspheres With Patterned Surface Structures

In recent years, magnetic composite microspheres and organicinorganic composite materials with patterned surface structures have attracted growing attention due to their potential applications. Preparation of composite microspheres with patterned surface structures integrated with super-paramagnetism has seldom reported in literatures. Based upon this consideration, a new strategy for preparing composite materials via introducing magnetism into template in a manner of outer and inner sediment on/in microspheres was proposed in our laboratory, and a series of the magnetic composite micrspheres exhibiting novel surface morphologies, which have excellent magnetic responsibility, and easiness in the chemical modification of their surfaces, were successfully created by simply varying kinds of aggradations and the ratio of the two monomer units in the template microgels, etc. respectively.On the bases of the above-mentioned research works conducted in our laboratory and the review (Chapter 1) on magnetic composite microspheres and composite materials with patterned surface structures, several magnetic composite microspheres were designed and prepared. It has been demonstrated that the magnetic responsibilities and surface structures of the microspheres we produce can be adjusted via various ways. The main works conducted in my thesis are outlined below.First, N-isopropylacrylamide (NIPAM) and acrylic acid (AA) copolymer microgels P(NIPAM-co-AA) of different amount of AA were prepared by employing a reverse suspension polymerization technique. The polymeric microgels were used firstly as micro-containers to include Fe₃O₄ nano-particles and then as micro-reactors to control the hydrolysis of tetraethyl orthosilicate (TEOS). In this way, various superparamagnetic composite microspheres SiO₂-Fe₃O₄-P(NIPAM-co-AA) with different morphologies in the micrometer size range were prepared. It was demonstrated that the sensitivity of the composite microspheres to external magnetic field was controlled by the amount of Fe₃O₄ adding; the morphologies of the composite microspheres could be tailored to a certain extent by either varying the ratio of the two-monomer units in the template microgels or the amount of SiO₂ deposited. The more the amount of SiO₂ deposited, the more specific gravity of microspheres was, and then after calcined, thermal stabilities of the skeleton and morphologies of microspheres enhanced. Images of SEM and TEM show that the microspheres morphology is novel and perfect, Fe₃O₄ nano-particles were dispersed uniformly in the microgel templates and coated completely by SiO₂. Statistic results of microspheres size indicated that the particles sizes are about 35μm and occupied a good monodispersity. The excellent magnetic responsibility of the composite microspheres, the easiness of modifying of the surfaces and the better biocompatibility of SiO₂ may make the microspheres find important uses in the mild separation of bioactive materials, loading of active materials, and radiation and shock absorption, etc.Considering the fact that the morphologies and performance of magnetic composite microspheres depend on the depositing methods and the microgels templates, the swelling method was substituted with preparation of Fe₃O₄ in-situ during the preparation process of the magnetic composite microspheres. A series of magnetic composite microspheres with fine patterned surface structures were prepared and characterized. Compared with the microspheres mentioned above, the magnetic hysteresis loops of the composite microspheres are not identical, asymmetrical loop, which clearly revealed the presence of unidirectional exchange anisotropy, which can be understand by the interaction between an anti-ferromagnetic material and ferromagnetic material. Besides this work, we also introduced acrylamide (AM) and methyl acrylic acid (MAA) copolymer microgels as template, and got another kinds of composite microspheres with fancy morphology. The surface became smoother after calcinations. In general, simply adjusting the reaction condition could control the surface structures, the magnetic responsibility and the density of these magnetic microspheres. This offers a new strategy for designing and preparation of the super-paramagnetic composite microspheres with patterned surface structures.In the third part of this thesis, a lot of full-IPN urea-formaldehyde resinP(NIPAM-co-AA) (UFR-P(NIPAM-co-AA)) polymer composite microspheres with patterned surface structures were prepared by employing P(NIPAM-co-AA) microgel as a template. This organic-organic composite microspheres were designed and to be prepaed in order to extend the applications of the microspheres with patterned surface structures. The influence of acidity, concentration, the ratio of urea and formaldehyde on the surface pattern structures of the UFR-P(NIPAM-co-AA) composite microspheres were interrogated by using SEM and FTIR techniques. It was demonstrated that the morphologies of the polymer-polymer composite microspheres are determined by the initial ratios of urea to formaldehyde. As examples, the morphologies of the surfaces are characterized by a network and a dense deposit structures when the ratio are 1:2 and 3:1, respectively. Furthermore, these fancy pattern structures, which may offer a diversification template for preparing composite microspheres, make them worth to be exploited further.Acoustic absorbing test of the magnetic composite microspheres with patterned surface structures have been measured with an ultrasonic system, the magnetic composite materials. The magnetic microspheres were compounded into epoxy resin during the absorbing test. It shows good performance at high frequency ranges. It is anticipated that the magnetic composite microspheres may be used as novel materials for radiation absorbance and shock absorption.The main contributions of this thesis are as follow:(1) A swelling method was used firstly to introduce super-paramagnetic Fe₃O₄ nano-particles into polymeric microgel templates and via this way, a number of inorganic-organic composite microspheres of a size in the micrometer range with patterned surface structures and super-paramagnetic properties have been succefully prepared.(2) The patterns of the surface structures, the chemical properties of surface, and the magnetic responsibility of the composite microspheres could be adjusted in a great range, according to the methodology we established in this work.(3) The model for acoustic absorbing measurement of the panicles in micrometer or nanometer size range was proposed.