Control and detection of molecular dynamics in the diluted magnetic fluid solution under magnetic field.

磁流体是铁磁性微粒的胶体溶液，用表面活性剂覆盖在液体（水或有机溶剂）表面，使其分散。磁流体胶体的直径约为10 nm。当单层表面活性剂覆盖颗粒时，磁流体疏水并分散在非水溶剂中。当两层表面活性剂覆盖颗粒时，磁流体是亲水的，可溶于水。在本研究中，磁流体用含有荧光染料的溶剂稀释。我们假设磁流体粒子在磁场下产生团簇。当染料和磁流体颗粒之间的相互作用很强时，荧光染料分子与簇相关联。在这种情况下，它提供了在染料的偏振荧光强度的变化，通过激发与磁场平行偏振的光源。当使用水溶性磁流体（第一层表面活性剂为亚油酸，第二层表面活性剂为聚乙二醇十二烷基醚）时，罗丹明染料的荧光强度提高200%以上，而其他染料的荧光强度没有提高。此外，在磁场下，在稀释的磁流体（表面活性剂的第一层：油酸）的存在下，蒽衍生物的荧光强度的变化进行了研究。在这种情况下，荧光强度下降了约10%。虽然大多数蒽衍生物的荧光强度都有类似的下降幅度，但9,10-二甲基蒽的荧光强度下降幅度较大。另一方面，当激发和荧光垂直于磁场时，荧光增强。这些结果表明，由于染料和磁流体中使用的表面活性剂的亲和力，本方法可以分离染料分子。

Magnetic fluid is a colloid solution of the ferromagnetic fine particles which can be dispersed in the liquid (water or organic solvents) by covering their surfaces with surfactants. Diameter of the colloid of magnetic fluid is about 10 nm. When the single layr of the surfactant covers the particle, magnetic fluid is hydrophobic and dispersed in non-aqueous solvents. When the double layrs of the surfactant cover the particle, magnetic fluid is hydrophilic and soluble in water. In this study, the magnetic fluid was diluted with the solvent which contains the fluorescent dye. We assumed that the magnetic fluid particles produce clusters under the magnetic field. When the interaction between the dye and the magnetic fluid particle is strong, the fluorescent dye molecules are associated to the cluster. In this case, it provides a variation in the polarized fluorescence intensity of the dye by excitation of the light source polarized with parallel against the magnetic field. When water solube magnetic fluid (the first layr of surfactant : linoleic acid, the second layr of surfactant : polyethylene glycol lauryl ether) was used, the fluorescence intensity of Rhodamine dyes increased by over 200%, but other dye did not. Also, variations in the fluorescence in the intensities of anthracene derivatives under a magnetic field were investigated in the presence of a diluted magnetic fluid (first layr of the surfactant : oleic acid). In this case, the intensity of the fluorescence decreased by about 10%. Although the fluorescence intentisities of most of the anthracene derivatives showed a similar decrease in magnitude, that of 9,10-dimethylanthracene showed a large decrease. On the other hand, fluorescence increased when excitation and fluorescence were perpendicular to the magnetic field. These results show the possibility of the separation of the dye molecules due to the affinity specific to the dye and the surfactant used in the magnetic fluid y means of the present method.