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Computational Chemistry on Dynamic Properties of Ferromagnetic Colloidal Dispersions by Means of Stokesian Dynamics Method

斯托克斯动力学方法研究铁磁胶体分散体动力学性质的计算化学

基本信息

批准号：
12640560
负责人：
SATOH Akira
金额：
$ 1.86万
依托单位：
Akita Prefectural University
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (C)
财政年份：
2000
资助国家：
日本
起止时间：
2000 至 2001
项目状态：
已结题

项目摘要

(1) We have conducted Stokesian dynamics simulations to investigate the dynamic properties of ferromagnetic colloidal dispersions subjected to a sinusoidal shear flow. Thick chain-like cluster formation is significantly influenced by an oscillatory shear flow even if the amplitude is relatively small, since the internal structures of thick chain-like clusters are highly sensitive to the change in the direction of the shear flow. The motion of thick chain-like clusters is out of phase to a sinusoidal shear rate, and the phase difference is strongly correlated with that of the viscosity and normal stress coefficients. The viscoelastic properties become more apparent with decreasing frequency of the oscillatory shear flow, since such properties have a strong relationship with the thick chain-like cluster formation.(2) We have investigated the rheological properties and the orientational distributions of particles of a dilute colloidal dispersion, which is composed of ferromagnetic spheroc … More ylinder particles, subject to a simple shear flow. The orientational distribution function has a sharper peak for a stronger magnetic field, and the position of the peak changes from the flow direction to the magnetic field direction as the magnetic field comes to govern the shear flow. Since the orientation of the particle is highly restricted in the field direction as the magnetic field becomes strong, the viscosity increases significantly. The particles with a larger aspect ratio lead to the larger increment in the viscosity, since they induce a larger resistance in a flow field.(3) The characteristics and differences in the two approximations, I.e., the additivity of forces and the additivity of velocities, on which Stokesian dynamics methods are based, have been investigated. Stokesian dynamics simulations of a ferromagnetic colloidal dispersion have been carried out for a simple shear flow, and the aggregate structures and averaged viscosities have been evaluated. From the results of aggregate structures in equilibrium, the correlation functions obtained by the additivity of forces are quantitatively different from those by the approximation of ignoring hydrodynamic interactions, although a qualitative agreement is recognized. The results obtained by the additivity of velocities give medium characteristics between the two above approximations. The shape of the pair correlation function for the additivity of velocities approaches that for the additivity of forces as the influence of magnetic interactions decreases. From the results of transient characteristics from an initial state, the results by the additivity of velocities agree well with those by the additivity of forces. In contrast, the results without hydrodynamic interactions deviate from those of the two additivity approximations at a time step when a nearly particle-particle touching situation starts to appear. Less

(1)我们已经进行了斯托克斯动力学模拟研究铁磁胶体分散体受到正弦剪切流的动力学性质。即使振幅相对较小，厚链状簇的形成也受到振荡剪切流的显著影响，因为厚链状簇的内部结构对剪切流方向的变化高度敏感。粗链状团簇的运动在正弦剪切速率下是异相的，其相位差与粘度系数和法向应力系数的相位差有很强的相关性。随着振荡剪切流频率的降低，粘弹性性质变得更加明显，因为这种性质与粗链状簇的形成有很强的关系。(2)本文研究了由铁磁球组成的稀胶体分散体的流变特性和粒子的取向分布。 ...更多信息圆柱体颗粒，受到简单的剪切流。取向分布函数具有更尖锐的峰值，对于更强的磁场，并且峰值的位置从流动方向改变为磁场方向，因为磁场开始支配剪切流。由于随着磁场变强，颗粒的取向在磁场方向上受到高度限制，因此粘度显著增加。具有较大长径比的颗粒导致较大的粘度增量，因为它们在流场中引起较大的阻力。(3)分析了两种近似的特点和区别，即：研究了Stokes动力学方法所基于的力的可加性和速度的可加性。采用斯托克斯动力学方法模拟了简单剪切流场中铁磁性胶体分散体的聚集态结构和平均粘度。从平衡态聚集体结构的结果来看，由力的可加性得到的相关函数与忽略流体动力相互作用的近似得到的相关函数在数量上不同，尽管定性上一致。由速度的可加性得到的结果给出了介于上述两种近似之间的介质特性。随着磁相互作用的影响减小，速度可加性的对相关函数的形状接近力可加性的形状。从一个初始状态的瞬态特性的结果来看，由速度的可加性得到的结果与由力的可加性得到的结果一致。与此相反，没有流体动力学相互作用的结果偏离的两个可加性近似的时间步长时，几乎粒子接触的情况开始出现。少