Chemical and Biomolecular Engineering, Johns Hopkins University, Baltimore, Maryland 21286, USA.
Langmuir. 2011 Aug 2;27(15):9211-8. doi: 10.1021/la201478y. Epub 2011 Jun 28.
We report nonintrusive optical microscopy measurements of single micrometer-sized silica and polystyrene colloids in inhomogeneous AC electric fields as a function of field amplitude and frequency. By using a Boltzmann inversion of the time-averaged sampling of single particles within inhomogeneous electric fields, we sensitively measure induced dipole-field interactions on the kT energy scale and fN force scale. Measurements are reported for frequencies when the particle polarizability is greater and less than the medium, as well as the crossover between these conditions when dipole-field interactions vanish. For all cases, the measured interactions are well-described by theoretical potentials by fitting a nondimensional induced dipole-field magnitude. While silica dipole-field magnitudes are well-described by existing electrokinetic models, the polystyrene results suggest an anomalously high surface conductance. Sensitive measurements of dipole-field interactions in this work provide a basis to understand dipole-dipole interactions in particle ensembles in the same measurement geometry in part II.
我们报告了非侵入式光学显微镜测量，结果表明在非均匀交流电场中，单个微米大小的二氧化硅和聚苯乙烯胶体作为场幅度和频率的函数。通过使用玻尔兹曼反演在非均匀电场中单个粒子的时间平均采样，我们在 kT 能量尺度和 fN 力尺度上灵敏地测量了感应偶极场相互作用。报告了当颗粒介电常数大于和小于介质时的频率，以及当偶极场相互作用消失时这些条件之间的交叉。对于所有情况，通过拟合无量纲感应偶极场大小，测量到的相互作用都很好地符合理论势。虽然二氧化硅偶极场大小很好地符合现有的电动模型，但聚苯乙烯的结果表明表面电导率异常高。这项工作中对偶极场相互作用的敏感测量为在部分 II 中以相同的测量几何形状理解粒子系综中的偶极偶极相互作用提供了基础。
