Department of Chemistry, Physical and Theoretical Laboratory, University of Oxford, South Parks Road, Oxford OX1 3QZ, United Kingdom.
Department of Materials, ETH Zürich, 8093 Zurich, Switzerland.
Phys Rev E. 2023 Apr;107(4):L042602. doi: 10.1103/PhysRevE.107.L042602.
Anisotropic colloidal particles exhibit complex dynamics which play a crucial role in their functionality, transport, and phase behavior. In this Letter, we investigate the two-dimensional diffusion of smoothly curved colloidal rods-also known as colloidal bananas-as a function of their opening angle α. We measure the translational and rotational diffusion coefficients of the particles with opening angles ranging from 0^{∘} (straight rods) to nearly 360^{∘}(closed rings). In particular, we find that the anisotropic diffusion of the particles varies nonmonotonically with their opening angle and that the axis of fastest diffusion switches from the long to the short axis of the particles when α>180^{∘}. We also find that the rotational diffusion coefficient of nearly closed rings is approximately an order of magnitude higher than that of straight rods of the same length. Finally, we show that the experimental results are consistent with slender body theory, indicating that the dynamical behavior of the particles arises primarily from their local drag anisotropy. These results highlight the impact of curvature on the Brownian motion of elongated colloidal particles, which must be taken into account when seeking to understand the behavior of curved colloidal particles.
各向异性胶体颗粒表现出复杂的动力学行为，这些行为在其功能、输运和相行为中起着至关重要的作用。在这封信中，我们研究了光滑弯曲胶体棒（也称为胶体香蕉）的二维扩散，作为其开口角度α的函数。我们测量了具有从 0^{∘}（直棒）到近 360^{∘}（闭合环）的开口角的粒子的平移和旋转扩散系数。特别是，我们发现粒子的各向异性扩散与它们的开口角度呈非单调变化，并且当α>180^{∘}时，最快扩散轴从粒子的长轴切换到短轴。我们还发现，几乎闭合环的旋转扩散系数比相同长度的直棒高大约一个数量级。最后，我们表明实验结果与细长体理论一致，表明粒子的动力学行为主要源于其局部阻力各向异性。这些结果突出了曲率对长形胶体粒子布朗运动的影响，在试图理解弯曲胶体粒子的行为时，必须考虑这一影响。
