Department of Chemical and Biomolecular Engineering, Johns Hopkins University, Baltimore, Maryland 21286, USA.
Langmuir. 2011 Aug 2;27(15):9219-26. doi: 10.1021/la2014804. Epub 2011 Jun 28.
We report nonintrusive optical microscopy measurements of ensembles of polystyrene colloids in inhomogeneous AC electric fields as a function of field frequency and particle size. By using an inverse Monte Carlo (MC) simulation analysis of time-averaged particle microstructures, we sensitively measure induced dipole-dipole interactions on the kT energy 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-dipole interactions vanish. By using measured single dipole-field interactions and associated parameters from Part I as input in the inverse analysis, the dipole-dipole interactions in this work are accurately modeled with no adjustable parameters for conditions away from the crossover frequency (i.e., |f(CM)| > 0). As dipolar interactions vanish at the crossover, a single frequency-dependent parameter is introduced to account for microstructures that appear to result from weak AC electro-osmotic flow induced interactions. By connecting quantitative measures of equilibrium microstructures and kT-scale dipole-field and dipole-dipole interactions, our findings provide a basis to understand colloidal assembly in inhomogeneous AC electric fields.
我们报告了非侵入式光学显微镜测量非均匀交流电场中聚苯乙烯胶体聚集体的结果，实验测量结果与场频和颗粒尺寸有关。通过对时间平均粒子微结构的逆蒙特卡罗（MC）模拟分析，我们在 kT 能量标度上灵敏地测量了感应偶极-偶极相互作用。我们报道了在粒子极化率大于和小于介质的频率下的测量结果，以及在这些条件下偶极-偶极相互作用消失的交叉频率。通过在逆分析中使用第一部分中测量的单个偶极场相互作用和相关参数作为输入，在远离交叉频率（即 |f(CM)| > 0）的情况下，无需可调参数即可准确地对偶极-偶极相互作用进行建模。当偶极相互作用在交叉点处消失时，引入了一个单一的频率相关参数，以解释似乎由弱交流电渗流诱导相互作用引起的微观结构。通过连接平衡微观结构和 kT 尺度偶极-场和偶极-偶极相互作用的定量测量，我们的研究结果为理解非均匀交流电场中的胶体组装提供了基础。
