Department of Physics, Georgia Institute of Technology, Atlanta, Georgia 30332, USA.
Department of Physics, Emory University, Atlanta, Georgia 30322, USA.
J Chem Phys. 2017 Oct 7;147(13):134502. doi: 10.1063/1.4996733.
We observe the translational and rotational diffusion of dimer tracer particles in quasi-2D colloidal samples. The dimers are in dense samples of two different sizes of spherical colloidal particles, with the area fraction ϕ of the particles varying from dilute to nearly glassy. At low ϕ, rotational and translational diffusion have a ratio set by the dimer size, as expected. At higher ϕ, dimers become caged by their neighboring particles, and both rotational and translational diffusion become slow. For short dimers, we observe rapid reorientations so that the rotational diffusion is faster than the translational diffusion: the two modes of diffusion are decoupled and have different ϕ dependence. Longer dimers do not exhibit fast rotations, and we find that their translational and rotational diffusion stay coupled for all ϕ. Our results bridge prior results that used spheres (very fast rotation) and long ellipsoids (very slow rotation).
我们观察了准二维胶体样品中二聚体质点的平移和旋转扩散。这些二聚体存在于两种不同大小的球形胶体粒子的密集样品中，粒子的面积分数ϕ从稀相到近玻璃相变化。在低ϕ时，旋转和平移扩散的比值由二聚体的大小决定，这是预期的结果。在较高的ϕ时，二聚体被相邻粒子束缚，旋转和平移扩散都变得缓慢。对于短二聚体，我们观察到快速的重新取向，使得旋转扩散比平移扩散快：两种扩散模式解耦，具有不同的ϕ依赖性。较长的二聚体不会表现出快速的旋转，我们发现它们的平移和旋转扩散在所有ϕ下都保持耦合。我们的结果连接了之前使用球体（非常快速的旋转）和长椭球（非常缓慢的旋转）的结果。
