Mukhija Deshpremy, Solomon Michael J
Department of Chemical Engineering, University of Michigan, 3410 G.G. Brown, 2300 Hayward St., Ann Arbor, MI 48109-2136, USA.
J Colloid Interface Sci. 2007 Oct 1;314(1):98-106. doi: 10.1016/j.jcis.2007.05.055. Epub 2007 May 24.
We report an experimental method to characterize the dynamics of colloidal rods by measuring their rotation and translation in three dimensions with confocal microscopy. The method relies on solvent viscosification to retard dynamics to time scales that are compatible with 3D confocal optical microscopy. Because the method yields a full three-dimensional characterization of rod displacement and orientation, it is applicable to situations in which complex, anisotropic dynamics emerge. Examples include behavior in liquid crystal phases with both orientational and positional order, suspensions subjected to applied fields such as shear flow or sedimentation, and the emerging area of anisotropic particle dynamics. We demonstrate the performance of the method by quantifying the Brownian motion of fluorescent poly(methyl methacrylate) rods (aspect ratio, L/D=3.1 and 7.0) grafted with poly(dimethylsiloxane) stabilizer. The rods are dispersed at dilute concentration in a solvent mixture of viscosity 2.0 Pa s. Rod translational and rotational diffusivities are extracted from the measured translational mean square displacement of the centroid positions and of the rod unit vector u(t), respectively. Rod orientational dynamics are characterized relative to both their azimuthal and polar angles. Probability distributions for the translation and rotation in the frame of rod are computed from the measurements. Experimental values obtained agree well with theory available for the dynamics of isolated rods.
我们报告了一种实验方法，通过共聚焦显微镜测量胶体棒在三维空间中的旋转和平移来表征其动力学。该方法依靠溶剂增粘将动力学延迟到与三维共聚焦光学显微镜兼容的时间尺度。由于该方法能够对棒的位移和取向进行完整的三维表征，因此适用于出现复杂各向异性动力学的情况。示例包括具有取向和位置有序的液晶相中的行为、受到诸如剪切流或沉降等外加场作用的悬浮液，以及各向异性粒子动力学的新兴领域。我们通过量化接枝聚（二甲基硅氧烷）稳定剂的荧光聚（甲基丙烯酸甲酯）棒（长径比L/D = 3.1和7.0）的布朗运动来证明该方法的性能。这些棒以稀浓度分散在粘度为2.0 Pa·s的溶剂混合物中。棒的平移和旋转扩散系数分别从质心位置和平移均方位移以及棒单位矢量u(t)的测量值中提取。棒的取向动力学相对于其方位角和极角进行表征。根据测量结果计算棒坐标系中平移和旋转的概率分布。获得的实验值与孤立棒动力学的现有理论非常吻合。
