离子型CoFe_2O_4磁性液体的宏观链径分布

利用Massart法制备了体积分数为0.4%的CoFe2O4磁性液体,在100～800Oe(1Oe=79.5775A/m)均匀磁场中利用光学显微镜分别观察了磁性液体宏观链的形态,测出了宏观链链径的分布.发现磁性液体在磁场100～500Oe内,链径满足双正态分布.提出磁性液体成链是由双因素主导的.利用六角模型,并构造链体系的混合熵,将链体系自由能最小化,得出了两个平均链径与磁场的数值关系.根据计算结果提出,宏观链径显双正态分布时,磁性液体处于两相混合相,随着外磁场增加,磁性液体内本身存在的微小预团聚体作为链核成链方式,逐步变为磁性液体内类"气"的颗粒受磁场"压缩"成链方式,磁性液体微结构也由混合相向六角("固")相转变.

Macro-chain diameter distribution of ionic CoFe_2O_4 ferrofluid

CoFe2O4 ferrofluid with volume fraction 0.4% has been prepared by Massart＇s method.Conformations of macro-chains of ferrofluid in uniform magnetic field ranged from 100 to 800 Oe are observed with optical microscope, and the distribution of chain diameter is also measured.It is found that the distribution of chain diameter satisfies the bi-normal distribution under the field ranged from 100 to 500 Oe.It is two factors dominant the formation of chains.After constructing the system mixing entropy and minimizing the system free energy, the relations of two average chain diameters and magnetic field is obtained with the hexagon model.According with the results of calculation, the ferrofluid is in the mixtue phase while macro-chain diameters show the bi-normal distribution.With the increasing of external field, in the ferrofluid, the mode which the chains format with the secondary particles as the cores turns gradually into the one which the chains format with the ＂gas-like＂ particles being ＂compressed＂ in field.Then, the ferrofluid will be transformed from the mixture phase to hexagonal phase （or ＂solid＂ phase）.