Tuning The Size Of Magnetite Microspheres By Changing Reactant Mixing Process In Polyol Method And The Study Of Its Mechanism

Magnetite microspheres have been widely used in many biomedical fields,including cell separation, nucleic acid extraction, immunoassay, owning to theirunique physicochemical properties. These properties and applications strongly dependon the size of microspheres. Therefore, tunable synthesis of magnetite microspheres isof significant importance to its biomedical applications. Up to now, various strategies,including microemulsion polymerization, solvophobic interactions, and emulsionevaporation method, have been developed to prepare magnetic microspheres withcontrolled size. Recently, much attention has been directed to a polyol method for itscapacities in synthesizing magnetic microspheres with hydrophilic surfaces and a highmagnetic content in one pot.In the present work, we report a new approach to tune the size ofcarboxyl-functionalized magnetite microspheres in polyol process. In this approach,large-scale of magnetite microspheres have been synthesized with a high iron saltconcentration. The diameter of magnetite microspheres can be tuned from about300to about900nm by simply changing the reactant mixing process while keeping otherconditions constant. The results indicate that mild reactant mixing process producesFe₃O₄microspheres with large size while intensive mixing process produces smallermicrospheres. The reactant mixing process does not significantly change thecomposition, surface and magnetic properties of the Fe₃O₄microspheres. With a lowerreactant concentration, the reactant mixing process also significantly affects the sizeof the magnetic microspheres. To study the influence mechanism of reactant mixing process on the size of theFe₃O₄microspheres, optical microscope and Masterzier were used to analyze the sizeof particle aggregates in the mixtures obtained with different reactant mixingprocesses. The results show that particle aggregates with large size generate in themixture obtained with mild mixing process while aggregates with smaller sizegenerate with vigorous mixing process. The rheological measure indicates that anetwork structure formed between the aggregates in the mixture. And a quasi-in situobservation of the reactant shows that the reactant mixture turned into a gel after aperiod of reaction, and then collapsed with the prolonging of reaction time. Based onthe above results, the impact mechanism assumption of reactant mixing process on thesize of Fe₃O₄microspheres in polyol process is describe as followed: the mixingprocess impact the size of particle aggregates in the mixture, which in turn impacts thesize of the synthesized Fe₃O₄microspheres.