在化学共沉淀法合成Fe3 O4晶相初期加入过量油酸进行包覆，在碱性条件下获得了水基磁流体，通过加入酸或乙醇的简易方法，将亲水颗粒转变为亲油颗粒。对包覆改性后的颗粒进行傅里叶红外（FTIR）、热重（TG）、透射电镜（TEM）以及磁性能（VSM）的表征，结果表明：加入过量油酸形成了内层化学吸附，外层物理吸附的双层包覆结构，酸法改性通过外层羧基的质子化将颗粒转变为亲油性，保留了双层吸附结构，颗粒的失重率最大；TEM观察表明颗粒呈理想的单分散状态，所制备的正己烷磁流体较单层吸附情况下稳定性显著提高。%In this work,spinel Fe3 O4 magnetic nano particles were synthesized by chemical co-precipita-tion method.The excess oleic acid was added during the initial stage of the reaction to prepare water-based ferrofluid under an alkaline condition.Subsequently,a novel and facile modified method were pro-posed by adding hydrochloric acid to adjust pH value or adding ethanol to successfully change the bilayer-coated hydrophilic particles to hydrophobic ones.The coated particles were characterized by Fourier infra-red spectrometer (FTIR),thermogravimetry analyzer (TG),transmission electron microscopy (TEM) and vibrating sample magnetometer (VSM).The results showed that the prepared water-based ferrofluid had the formation of inner layer chemical and outer layer physical adsorption by oleic acid and the particles' bilayer-coated structure was maintained by the acid modification through protonating the termi-nal carboxyl group,which had the maximum weight loss rate.The bilayer-coated Fe3 O4 particles were monodispersed in hexane indicated in TEMimage.The stability of the ferroluid was much better than that of single coated particles because of the space steric effects'promotion caused by the bilayer-coated struc-ture.
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