Kluijtmans SG, Koenderink GH, Philipse AP
Van't Hoff Laboratory for Physical and Colloid Chemistry, Debye Research Institute, Utrecht University, Padualaan 8, 3584 CH Utrecht, The Netherlands.
Phys Rev E Stat Phys Plasmas Fluids Relat Interdiscip Topics. 2000 Jan;61(1):626-36. doi: 10.1103/physreve.61.626.
Long-time self-diffusion and sedimentation of fluorescent tracer spheres in electrostatically stabilized dispersions of rigid colloidal host rods have been measured in situ with fluorescence recovery after photobleaching, and gravitational and ultracentrifugal sedimentation. The dynamics of silica tracer spheres of 39 and 370 nm radius was monitored in dispersions of host rods with aspect ratios 9.6 and 25.7 at various rod volume fractions. The translational and rotational diffusion coefficient of the host rods was obtained independently with dynamic light scattering and birefringence decay measurements. Our results indicate that sedimentation and long-time self-diffusion are determined by the same friction factor. Furthermore we find that, as long as the host rods are relatively mobile, tracer sphere sedimentation and long-time self-diffusion are governed by the macroscopic solution viscosity, regardless of the tracer and host rod size. However, when the host rods are immobilized, due to rod entanglements at higher volume fractions, tracer sphere dynamics depends strongly on the tracer size relative to the pore size of the host rod network. The large tracers are completely trapped in the network whereas the small tracer spheres remain mobile. Current models for tracer sphere motion in rod assemblies do not satisfactorily explain the complete dynamic regime covered by our experimental model system because the effect of host rod mobility is not properly taken into account.
利用光漂白后的荧光恢复技术以及重力沉降和超速离心沉降，原位测量了刚性胶体主体棒状粒子静电稳定分散体系中荧光示踪球体的长时间自扩散和沉降。在不同棒状粒子体积分数下，监测了半径为39纳米和370纳米的二氧化硅示踪球体在长径比分别为9.6和25.7的主体棒状粒子分散体系中的动力学。通过动态光散射和双折射衰减测量，独立获得了主体棒状粒子的平动和转动扩散系数。我们的结果表明，沉降和长时间自扩散由相同的摩擦系数决定。此外，我们发现，只要主体棒状粒子相对可移动，示踪球体的沉降和长时间自扩散就由宏观溶液粘度控制，而与示踪粒子和主体棒状粒子的尺寸无关。然而，当主体棒状粒子因在较高体积分数下发生缠结而固定时，示踪球体的动力学强烈依赖于示踪粒子尺寸与主体棒状粒子网络孔径的相对大小。大的示踪粒子完全被困在网络中，而小的示踪球体仍可移动。目前关于示踪球体在棒状粒子聚集体中运动的模型不能令人满意地解释我们实验模型系统所涵盖的完整动力学范围，因为没有正确考虑主体棒状粒子可移动性的影响。
