Eloi M T A, Santos J L, Morais P C, Bakuzis A F
Instituto de Física, Universidade de Brasília, DF, Brazil.
Phys Rev E Stat Nonlin Soft Matter Phys. 2010 Aug;82(2 Pt 1):021407. doi: 10.1103/PhysRevE.82.021407. Epub 2010 Aug 24.
The field dependence of the optical transmission of tartrate-coated and polyaspartate-coated magnetite-based aqueous colloids was studied. The colloidal stock samples were diluted to prepare a series of samples containing different particle volume fractions ranging from 0.17% up to 1.52% and measured at distinct times after preparation (1, 30, 120, 240, and 1460 days). We show that the magneto-transmissivity behavior is mainly described by the rotation of linear chains, at the low-field range, whereas the analysis of the data provided the measurement of the average chain length. Results also reveal that the optical transmissivity has a minimum at a particular critical field, whose origin is related to the onset of columns of chains built from isolated particle chains, i.e., due to a columnar phase transition. We found the critical field reducing as the particle volume fraction increases and as the sample's aging time increases. To investigate the origin of this phenomenon we used phase condensation models and Mie's theory applied to a chain of spheres and to an infinite cylinder. Possible implications for magnetophotonic colloidal-based devices and biomedical applications were discussed.
研究了酒石酸盐包覆和聚天冬氨酸包覆的磁铁矿基水胶体的光传输的场依赖性。将胶体原液样品稀释以制备一系列含有不同颗粒体积分数（范围从0.17%到1.52%）的样品，并在制备后的不同时间（1、30、120、240和1460天）进行测量。我们表明，在低场范围内，磁透射率行为主要由线性链的旋转来描述，而对数据的分析提供了平均链长的测量值。结果还表明，光透射率在特定的临界场处有最小值，其起源与由孤立颗粒链构建的链柱的开始有关，即由于柱状相变。我们发现临界场随着颗粒体积分数的增加和样品老化时间的增加而降低。为了研究这种现象的起源，我们使用了相凝聚模型以及应用于球形链和无限长圆柱体的米氏理论。讨论了对基于磁光子胶体的器件和生物医学应用的可能影响。
