Synthesis And Electrorheological Effect Of Polystyrene Microspheres On Rare Earth Hybrid Surface

Recently, considerable attention has been focused on the development of functional polymer microspheres by polymerization. The latexes with functional groups can be used to graft inorganic materials to form hybrid materials.The lanthanides present various unique chemical properties that are favorable for research of photoelectric materials, biological materials and other new materials and interest in their applications is increasing. Electrorheological fluids (ERF) are fascinating materials whose structure and rheological properties are dramatically altered by an external electric field. The rheological properties of an ER suspension could reversibly change in several orders of magnitude under an external electric field of several kilovolts per millimeter. Since its mechanical properties can be easily controlled within a wide range almost from pure liquid to solid, the ER fluid could be used as various electromechanical control equipments. Unfortunately, some available ER materials, some with relatively low shear stress and narrow operating temperature, some with poor suspension stability, are not satisfactory in engineering. Recent inclusion of nano or sub-micron particles within ER fluids has shown a relationship to favorable ER trends. The optimization of ER fluid performance depends on the chemical and structural compositions of the particles in suspension and the suspension itself. Therefore, the development of high performance ER fluids via optimizing and tuning conducting materials has been a main subject of considerable interest for the application. Based on this point, our aim is to obtain hybrid polystyrene microspheres with surface rare earth complexes and study on their ER behaviors or effects. The main results obtained are shown as follows:1. Synthesis of carboxyl polystyrene monodisperse microspheres via emulsifier-free emulsion copolymerizationThe soap-free emulsion copolymerization of styrene with carboxylic acid was conducted in presence of sodium p-styrenesulfonate (NaSS) using a mixture of water and methanol as the dispersing medium. The resulting carboxyl polystyrene microspheres, due to a large number of surface bound-COOH groups, possessed high surface electric charges in a monodisperse style, which were fully characterized using TEM, SEM, FT-IR, DLS and solid-state NMR. Many parameters for the co-polymerization, such as the concentrations of styrene (St) and NaSS, the ratio of DVB/St, and the solvent composition were discussed in details. Here the carboxyl acids included p-vinyl benzoic acid (VBA), acrylic acid (AA), methacrylic acid (MAA), and itaconic acid (IA).FT-IR spectra and solid-state NMR spectrum confirmed the presence carboxyl groups located on the surface of polymer microspheres. TEM images and DLS results showed that the polymer particles were monodisperse microspheres. With the increasing concentration of NaSS, the fraction of NaSS in the polymer chains would increase, more latex particles could be formed and the particle size deceased. The presence of methanol could facilitate the oligomer nucleation and adsorption, and relatively larger particles were formed at higher methanol content. To some extent, the influence on particle-size of NaSS was obviously bigger than that of mass ratio of methanol/water. The more St concentration increased, the more St monomers absorbed, the more particle size grew. At the same time, the particle size was slightly influenced by the polarity of the reaction medium when DVB was added.2. Synthesis of hybrid polystyrene microspheres with surface rare earth complexes via direct coordination of rare earth ionsHybrid polystyrene microspheres with surface rare earth complexes were easily fabricated from carboxyl polystyrene particles and aqueous rare earth ion solution in the presence of triethylamine, due to the negative charges on the surface of microspheres coordinated with rare earth ion. The rare earth elements included terbium (Tb), europium (Eu), cerium (Ce), samarium (Sm), lanthanum (La), gadolinium (Gd), yttrium (Y) and neodymium (Nb). Various methods, including TGA, TEM, SEM-EDS, ICP-OES, EPR, SEM and FT-IR, were used to characterize the resultant polystyrene composite microspheres.FT-IR spectra could confirm that the rare earth ions were successfully coordinated with the carboxylic groups on the polymer microspheres. The results of TG and EPR confirmed such conclusion from another perspective. TEM images showed that the rare earth ions binding to the surface of the microspheres didn’t lead to obvious changes in the morphologies of them. The result of SEM-EDS was usually more than that of ICP-OES; maybe it was due to the lack of representative of analytical area in SEM-EDS, partly indicating the rare earth ions amount on the surface of microspheres. On the other hand, the result of ICP-OES presented the whole amount of rare earth ions, in our case, equivalent to the rare earth ions amount on the surface, so the results of ICP-OES were selected as judgment in the whole experiment. The reaction factors which influenced the coordination of rare earth ions with carboxyl groups on the surface of hybrid polystyrene microspheres included solvent, pH value, reaction temperature, time, rare earth ions concentration and so on.3. Synthesis of hybrid polystyrene microspheres with surface rare earth complexes, based on non "polymerization-coordination" methodsFirst, direct co-polymerization of styrene with a rare earth-containing precursor was used to fabricate hybrid particles; such precursors included Gd (MAA)3and Eu (MAA)3phen. TEM images showed that resultant polymer particles were microspheres too. The result of SEM-EDS also indicated that there had been rare earth ions complex on the surface of hybrid microspheres.Second, rare earth hybrid microspheres were synthesized by using poly (St-co-AA) microspheres combined with CeO2nanopowders. TEM images showed that CeO2nanoparticles had been doped onto the surface of poly (St-co-AA). The results of SEM-EDS indicated that there had been rare earth ions complex formation on the surface of hybrid microspheres.4. Study on the electrorheological effects of hybrid polystyrene microspheres with surface rare earth complexesThe hybrid polystyrene microspheres prepared above were used as dispersed phase in ER fluids respectively. Methyl silicone oil and hydroxyl silicone oil were used as liquid phase respectively. The rheological properties of such ER suspension under an external direct-current electric field were investigated respectively too. The results showed that the species of carboxylic acids and rare earth elements had different degree of influences on such properties. Based on the composite polystyrene microspheres as dispersed phase, obtained with VBA as co-monomer, such electrorheological suspension showed the best positive electrorheological effect.