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) 我们进行了斯托克斯动力学模拟，以研究铁磁胶体分散体在正弦剪切流作用下的动态特性，即使振幅相对较小，粗链状簇的形成也会受到振荡剪切流的显着影响，因为内部的内部结构。粗链状团簇的结构对剪切流方向的变化高度敏感，粗链状团簇的运动与正弦剪切异相。速率，相位差与粘度和法向应力系数密切相关，随着振荡剪切流频率的降低，粘弹性特性变得更加明显，因为这种特性与粗链状簇的形成有很强的关系。 (2) 我们研究了稀胶体分散体颗粒的流变特性和取向分布，该分散体由铁磁球体圆柱体颗粒组成，受到简单的影响剪切流的方向分布函数对于更强的磁场具有更尖锐的峰值，并且随着磁场开始控制剪切流，峰值的位置从流动方向改变到磁场方向。当磁场变强时，在场方向上受到高度限制，粘度显着增加，具有较大纵横比的颗粒导致粘度增量更大，因为它们在流场中产生更大的阻力。（3）两者的特点和区别斯托克斯动力学方法所基于的近似，即力的可加性和速度的可加性，已经针对简单的剪切流、聚集结构和平均进行了铁磁胶体分散体的斯托克斯动力学模拟。从平衡状态下的聚集体结构的结果评估了粘度，通过力的相加性获得的相关函数与通过力的相加获得的相关函数在数量上有所不同。忽略流体动力相互作用的近似，尽管认识到了定性的一致性，通过速度的可加性获得的结果给出了上述两个近似之间的介质特征。速度的可加性的成对相关函数的形状接近于力的可加性的形状。从初始状态的瞬态特性结果来看，速度相加性的结果与力相加性的结果非常吻合。当几乎粒子与粒子接触的情况开始出现时，没有流体动力学相互作用的结果在时间步上偏离了两个可加性近似的结果。