Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, California 91125, USA.
J Chem Phys. 2011 Jul 7;135(1):014701. doi: 10.1063/1.3604530.
We employ an analogy to traditional dynamic light scattering to describe the inhomogeneous and anisotropic diffusion of colloid particles near a solid boundary measured via evanescent wave dynamic light scattering. Following this approach, we generate new expressions for the short-time self- and collective diffusivities of colloidal dispersions with arbitrary volume fraction. We use these expressions in combination with accelerated Stokesian dynamics simulations to calculate the diffusivities in the limit of large and small scattering wave numbers for evanescent penetration depths ranging from four particle radii to one-fifth of a particle radius and volume fractions from 10% to 40%. We show that at high volume fractions, and larger penetration depths, the boundaries have little effect on the dynamics of the suspension parallel to the wall since, to a first approximation, the boundary acts hydrodynamically much as another nearby particle. However, near and normal to the wall, the diffusivity shows a strong dependence on penetration depth for all volume fractions. This is due to the lubrication interactions between the particles and the boundary as the particle moves relative to the wall. These results are novel and comprehensive with respect to the range of penetration depth and volume fraction and provide a complete determination of the effect of hydrodynamic interactions on colloidal diffusion adjacent to a rigid boundary.
我们采用类似于传统动态光散射的方法来描述通过消逝波动态光散射测量的胶体粒子在固体边界附近的非均匀各向异性扩散。根据这种方法，我们为具有任意体积分数的胶体分散体生成了短时间自扩散和集体扩散系数的新表达式。我们使用这些表达式结合加速 Stokesian 动力学模拟，计算了在消逝穿透深度从四个粒子半径到五分之一粒子半径以及体积分数从 10%到 40%的大散射波数和小散射波数极限下的扩散系数。我们表明，在高体积分数和较大的穿透深度下，边界对平行于壁面的悬浮液动力学几乎没有影响，因为边界在流体动力学上近似于另一个附近的粒子。然而，在靠近壁面和垂直于壁面的方向上，对于所有的体积分数，扩散系数都强烈依赖于穿透深度。这是由于粒子相对于壁面运动时粒子与边界之间的润滑相互作用所致。这些结果在穿透深度和体积分数的范围内是新颖而全面的，提供了对刚性边界附近胶体扩散中流体动力相互作用影响的完整确定。
