Verweij Ruben W, Ketzetzi Stefania, de Graaf Joost, Kraft Daniela J
Huygens-Kamerlingh Onnes Laboratory, Leiden University, P.O. Box 9504, 2300 RA Leiden, The Netherlands.
Institute for Theoretical Physics, Center for Extreme Matter and Emergent Phenomena, Utrecht University, Princetonplein 5, 3584 CC Utrecht, The Netherlands.
Phys Rev E. 2020 Dec;102(6-1):062608. doi: 10.1103/PhysRevE.102.062608.
Geometric confinement strongly influences the behavior of microparticles in liquid environments. However, to date, nonspherical particle behaviors close to confining boundaries, even as simple as planar walls, remain largely unexplored. Here, we measure the height distribution and orientation of colloidal dumbbells above walls by means of digital in-line holographic microscopy. We find that while larger dumbbells are oriented almost parallel to the wall, smaller dumbbells of the same material are surprisingly oriented at preferred angles. We determine the total height-dependent force acting on the dumbbells by considering gravitational effects and electrostatic particle-wall interactions. Our modeling reveals that at specific heights both net forces and torques on the dumbbells are simultaneously below the thermal force and energy, respectively, which makes the observed orientations possible. Our results highlight the rich near-wall dynamics of nonspherical particles and can further contribute to the development of quantitative frameworks for arbitrarily shaped microparticle dynamics in confinement.
几何限制对液体环境中微粒的行为有强烈影响。然而，迄今为止，即使是靠近诸如平面壁这样简单的限制边界的非球形粒子行为，在很大程度上仍未得到探索。在这里，我们通过数字同轴全息显微镜测量壁上方胶体哑铃的高度分布和取向。我们发现，较大的哑铃几乎与壁平行取向，而相同材料的较小哑铃却令人惊讶地以特定角度取向。我们通过考虑重力效应和静电粒子 - 壁相互作用来确定作用在哑铃上的总高度相关力。我们的模型表明，在特定高度，哑铃上的净力和扭矩分别同时低于热力和热能，这使得观察到的取向成为可能。我们的结果突出了非球形粒子丰富的近壁动力学，并可为受限环境中任意形状微粒动力学的定量框架的发展做出进一步贡献。
