利用单光束光镊分别对水溶液及磁性液体中的SiO2小球进行光操纵和光学组装.实验结果表明：在相同激光功率作用下, SiO2小球在水溶液中只能组装成二维结构;而在磁性液体中, 小球的组装从二维组装过渡到三维组装.利用流体力学斯托克斯定律, 实验测量SiO2小球在不同溶液中所受切向梯度力的径向分布情况.利用扫描电镜表征SiO2小球在磁性液体中组装形成的三维结构发现, 有大量的磁性纳米颗粒包覆在SiO2小球的表面, 磁性纳米颗粒包覆层的形成提高了SiO2小球在光力作用下自组装的效率、有序性和稳定性.

The optical trapping and the self-assembly of silica spheres suspended in the Fe3O4 magnetic fluid were investigated by using a single focused laser beam. It is found that a three dimensional and ordered assembly of silica spheres can be realized in the magnetic fluid while only a two dimensional assembly can happen in aqueous solution of silica spheres with the same laser power. The transversal gradient forces exerted on the silica spheres were determined with the Stokes' law when the silica spheres dispersed in the magnetic fluid and in the water, respectively. It is shown that the transversal gradient forces acting on silica spheres suspended in the magnetic fluids are smaller than that on the silica spheres suspended in water due to the increase of the effective permittivity of surrounding medium. In addition, the morphologies of the assembling structure were investigated with SEM. It is shown that the silica spheres are covered with a layer of magnetic nanoparticles which dramatically enhances the efficiency, the ordering and the stability of the assembly.