Preparation of Ultrafine Magnetic Particles Using Microemul-sions and Vesicles

近年来，人们对均匀尺寸的超细磁性氧化物的需求不断增加，这些氧化物主要用于计算机数据存储、音频和视频记录、磁流体和某些微波器件的制造。磁性氧化物纳米颗粒制备的困难之处在于它们的制备大多是在散装水介质中进行的，在这种介质中无法阻止不受控制的成核和晶粒生长。这些化合物(γ - fe2o3, Fe3O4, CrO2，钴掺杂Fe2O3和钡铁氧体)在受限的微反应器中，如油包水微乳液的水芯或单室囊泡的内部部分，似乎是一个有前途的替代方案，尽管这些技术仍在发展中。本课题通过适当调节微乳和囊泡体系的某些理化条件，优化和控制微乳和囊泡体系的超低粒径和窄粒径分布。此外，该项目还研究了如何在产品微粒的形态（尺寸、形状和尺寸分布）和结构与表面活性剂体系的物理化学性质之间建立定量关联。研究结果描述了两种类型的微反应器（微乳液和微泡）在化学反应方面的异同。从这种微反应器中得到的固体沉淀物可能不同于在大的含水介质中沉淀的固体沉淀物。这些实验不仅可能导致单分散超细磁性颗粒的产生，而且还可能为微反应器中与成核和晶体生长有关的界面化学提供更大的基础理解。该项目利用了两个研究小组（罗德岛和佛罗里达大学）的专业知识。

In recent years, there has been an increasing demand for the preparation of ultrafine magnetic oxides of uniforms size which are mainly used in computer data storage, audio and video recording, magnetic fluids and fabrication of certain microwave devices. The difficulty of obtaining uniform-sized nanoparticles of magnetic oxides stems from the fact that their preparations are mostly done in bulk aqueous media in which uncontrolled nucleation and grain growth cannot be prevented. Synthesis of these compounds (gamma-Fe2O3, Fe3O4, CrO2, Cobalt doped Fe2O3 and barium ferrite) in constrained microreactors such as the aqueous cores of water-in-oil microemulsions or the inner part of single-compartment vesicles seems to be a promising alternative although these techniques are still under development. In this project, methods are used to optimize and control the ultralow size and the narrow particle size distribution by proper modulation of certain physico-chemical conditions of the microemulsion and vesicular systems. Further, the project examines how to make quantitative correlations between the morphology (size, shape, and size-distribution) and structure of the product microparticles and the physico-chemical properties of the surfactant system. The results of the study delineate the similarities as well as the differences between the two types of microreactors (microemulsions and vesicles) in relation to chemical reactions in them. The solid precipitate obtained from such microreactors may be different from that precipitated in a large aqueous medium. Not only might these experiments lead to the production of monodispersed ultrafine magnetic particles, but they might also provide a greater fundamental understanding of interfacial chemistry in relation to nucleation and crystal growth in microreactors. This project exploits the expertise of two research groups (Rhode Island and University of Florida).