With Multiple Electromagnetic Ph Sensitivity Of The Fe <sub> 3 </ Sub> The O <sub> 4 </ Sub> / Polymer Magnetic Microspheres Design, Construction And Characterization

Electromagnetic polymer microspheres as a new type of functional materials are a polymeric microsphere with electronic and magnetic response prepared by combining organic polymers with inorganic materials (Fe₃O₄, Fe₂O₃, Fe-Co) based on a microencapsulation method. Compared with conventional microspheres, the electromagnetic polymer microspheres bear many characteristics of polymers and electromagnetic response such as their surface functional groups and superparamagnetic properties etc., and thus can be quickly separated from the surrounding media or mixtures under the guidance of the magnetic field, which hint on us a new thread or idea for biological separation and detection, and bring about a new developing direction of functional materials. In recent years, magnetic polymer microspheres as a new type of functional materials have been extensively examined and exploited. Particularly, in the biomedical and biological engineering fields great attention has been aroused from researchers, which has become a hot topic in the realm of biomedicines. As the electromagnetic polymer microspheres can be combined with various functional molecules such as enzymes, antibodies, bacteria, DNA or RNA etc on their surface, and therefore assume broad application prospects in detection of pathogenic bacteria, protein purification, immobilized enzyme, targeted drug delivery, separation of nucleic acid research.In consideration of the above background, this study has done lots of work focusing on preparation, construction and characterization of functional magnetic polymer microspheres. Specifically, the work is dealt with the preparation and surface modification of Fe₃O₄ nanoparticles, core-shell magnetic polymer microspheres Fe₃O₄/P(MAA-MAH), as well as the preparation and characterization of a multi-layer core-shell structural magnetic polymer microspheres.1. Super-paramagnetic magnetite nanoparticles (Fe₃O₄) of about 10 nm were obtained by using an oleic acid and sodium dodecylbenzenesulfonate as modifiers based on chemical coprecipitation with superparamagnetic nanoparticles. The structure and magnetic properties were characterized by a Fourier transform-infrared (FT-IR), transmission electron microscopy (TEM), vibrating sample magnetometer (VSM) etc. The experimental results showed that the modified Fe₃O₄ nanoparticles exhibit good dispersion behavior on the basis of dual-surfactants, and the Fe₃O₄ size can be controlled by changing the reaction time, stirring speed of which the stirring speed have an important effect. X-ray diffraction (XRD) confirms that the as-prepared Fe₃O₄ nanoparticles show themselves spherical grains with cubic spinel structure.2. A typical core-shell structural microsphere, Fe₃O₄/P(MA-co-MAA), was prepared through a dispersion polymerization process using the modified Fe₃O₄ as a core and poly(maleic anhydride-co-methacrylic acid)(P(MA-co-MAA), as a shell coated on the surface of Fe₃O₄ nanoparticles. FT-IR, XRD and TEM observations indicated that the (P(MA-co-MAA)copolymer has successfully covered the Fe₃O₄ nanoparticles, and P(MA-co-MAA)/Fe₃O₄ miceospheres bear a marked core-shell structure characteristic. The characterization by VSM revealed that the coated magnetic microspheres have higher saturation magnetization than the pure Fe₃O₄, which favors drug controlled release via their magnetic properties.3. A novel multi-layered polymer microsphere, Fe₃O₄/PPy/P(MAA-co-AAm), with electric, magnetic and pH response was constructed by an oxidation polymerization route of pyrrole in a ferric chloride solution in view of common ion effect and subsequently by a free radical micro-emulsion copolymerization of MAA and NVP. At the same time, a new type of Fe₃O₄/PANI/P(MAA-co-NVP) multilayered composite microsphere was tailored by a coupling reaction of MDI anchor molecule based on a grandual polymerization principle as well as the same reaction mechanisum as the above mentioned. The as-prepared materials were characterized by various means, and the effect of different PANI molecular weight, component ratios of PANI or PPy to Fe₃O₄, etc on electric, magnetic, light, thermal and pH response was investigated. FT-IR, TEM, TGA and UV-vis findings prove that the as-prepared composite microspheres are characterized by designable spherical core-shell structure, and relatively strong interaction exists among the three layers and the microspheres therefore reflect good thermal stability. The VSM analysis testifies that the magnetic microspheres bear superparamagnetic, and the saturation magnetization of Fe₃O₄/PPy nanoparticles is increased from 27.9 to 32.52 emu·g^-1 with increasing Fe₃O₄ contents, while for Fe₃O₄/PANI nanoparticles, the value is from 36.18 emu·g^-1 up to 37.45 emu·g^-1. The saturation magnetization of Fe₃O₄/PPy/P(MAA-co-AAm) copolymer microspheres is decreased by 5.27 emu·g^-1 while he use of four-point resistance whereas the value for Fe₃O₄/PANI/P(MAA-co-AAm) tri-layered copolymer microspheres is 10.23 emu·g^-1. The four-probe resistance measurement confirmed that the conductivity of the Fe₃O₄/PANI/P(MAA-co-NVP) tri-layered microspheres increases from 1.301×10^-7 to 4.648×10^-5 S·cm^-1 with the increase in the content of conductive filler PANI, while for Fe₃O₄/PPy the value is from 8.9×10^-4 to 3.4×10^-3 S·cm^-1. The swelling in various PBS solutions and particle dimension analyses demonsrated that the magnetic microspheres display pH response. Therefore the multi-layered magnetic microspheres possess electric, magnetic and pH responsive multifunctionality, and can be well tailored or mediated by structure design, type of conductive fillers including their molecular weight, the component ratios etc. It is expected to be widely used in biomedicine, cytology and bioengineering etc. as separation materials and carriers for cell separation, enzyme immobilization, immunoassay, target drug and so on.