Holographic characterization and tracking of colloidal dimers in the effective-sphere approximation
Holographic characterization and tracking of colloidal dimers in the effective-sphere approximation
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DOI：
10.1039/d0sm02262d
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发表时间：
2021-03-14
期刊：
影响因子：
3.4
通讯作者：
Grier, David G.
中科院分区：
文献类型：
--
作者：
Altman, Lauren E.;Quddus, Rushna;Grier, David G.
利用Lorenz-Mie光散射理论分析胶体球体的同轴全息图，可以测量出纳米级精度的球体的三维位置，同时也可以测量出球体的直径和折射率，精度为千分之一。将同样的技术应用于非球面或非均匀粒子，可以测量出有效球体的位置、直径和折射率，代表粒子的几何形状和组成的平均值。这种有效球体的解释已经成功地应用于多孔、凹陷和涂层球体，以及纳米颗粒的分形团簇，所有这些不均匀现象都出现在小于光波长的长度尺度上。在这里，我们结合数值和实验研究来研究微米级球体对称二聚体的有效球特性，微米级球体是一类在现实世界中常见的非球面物体。我们的研究表明，在单分散胶体球的全息表征研究中，有效球解释有助于区分小的胶体团簇。对二聚体轴向位置的有效球面估计与其质心的地面真实情况密切相关。此外，有效球直径和折射率的趋势可以用来测量二聚体的三维取向。当应用于Poiseuille流中传输的胶体二聚体时，估计的取向分布与布朗粒子经历Jeffery轨道的预期一致。
An in-line hologram of a colloidal sphere can be analyzed with the Lorenz-Mie theory of light scattering to measure the sphere's three-dimensional position with nanometer-scale precision while also measuring its diameter and refractive index with part-per-thousand precision. Applying the same technique to aspherical or inhomogeneous particles yields measurements of the position, diameter and refractive index of an effective sphere that represents an average over the particle's geometry and composition. This effective-sphere interpretation has been applied successfully to porous, dimpled and coated spheres, as well as to fractal clusters of nanoparticles, all of whose inhomogeneities appear on length scales smaller than the wavelength of light. Here, we combine numerical and experimental studies to investigate effective-sphere characterization of symmetric dimers of micrometer-scale spheres, a class of aspherical objects that appear commonly in real-world dispersions. Our studies demonstrate that the effective-sphere interpretation usefully distinguishes small colloidal clusters in holographic characterization studies of monodisperse colloidal spheres. The effective-sphere estimate for a dimer's axial position closely follows the ground truth for its center of mass. Trends in the effective-sphere diameter and refractive index, furthermore, can be used to measure a dimer's three-dimensional orientation. When applied to colloidal dimers transported in a Poiseuille flow, the estimated orientation distribution is consistent with expectations for Brownian particles undergoing Jeffery orbits.