Materials and Manufacturing Directorate, Air Force Research Laboratory, Wright-Patterson AFB, Ohio 45433-7702, USA.
Nano Lett. 2010 Apr 14;10(4):1433-9. doi: 10.1021/nl100345u.
For nanoparticle-based technologies, efficient and rapid approaches that yield particles of high purity with a specific shape and size are critical to optimize the nanostructure-dependent optical, electrical, and magnetic properties, and not bias conclusions due to the existence of impurities. Notwithstanding the continual improvement of chemical methods for shaped nanoparticle synthesis, byproducts are inevitable. Separation of these impurities may be achieved, albeit inefficiently, through repeated centrifugation steps only when the sedimentation coefficient of the species shows sufficient contrast. We demonstrate a robust and efficient procedure of shape and size selection of Au nanoparticles (NPs) through the formation of reversible flocculates by surfactant micelle induced depletion interaction. Au NP flocculates form at a critical surfactant micelle molar concentration, C(m)* where the number of surfactant micelles is sufficient to induce an attractive potential energy between the Au NPs. Since the magnitude of this potential depends on the interparticle contact area of Au NPs, separation is achieved even for the NPs of the same mass with different shape by tuning the surfactant concentration and extracting flocculates from the sediment by centrifugation or gravitational sedimentation. The refined NPs are redispersed by subsequently decreasing the surfactant concentration to reduce the effective attractive potential. These concepts provide a robust method to improve the quality of large scale synthetic approaches of a diverse array of NPs, as well as fine-tune interparticle interactions for directed assembly, both crucial challenges to the continual realization of the broad technological potential of monodispersed NPs.
对于基于纳米粒子的技术，高效快速的方法对于优化纳米结构的光学、电学和磁学性质至关重要，因为这些方法可以得到高纯度、具有特定形状和尺寸的粒子，从而避免由于杂质的存在而产生偏见的结论。尽管化学方法在形状可控的纳米粒子合成方面不断得到改进，但副产物仍然不可避免。只有当物种的沉降系数表现出足够的对比时，通过重复离心步骤才能有效地分离这些杂质。我们通过表面活性剂胶束诱导的耗尽相互作用形成可逆聚集体，展示了一种用于金纳米粒子（Au NPs）的形状和尺寸选择的强大而高效的方法。Au NP 聚集体在临界表面活性剂胶束摩尔浓度 C(m)*下形成，在该浓度下，表面活性剂胶束的数量足以在 Au NPs 之间产生吸引力势能。由于这个势能的大小取决于 Au NPs 的颗粒间接触面积，因此即使是具有不同形状的相同质量的 NPs，通过调整表面活性剂浓度并通过离心或重力沉降从沉淀物中提取聚集体，也可以实现分离。然后通过降低表面活性剂浓度来重新分散细化后的 NPs，以降低有效吸引力势能。这些概念为提高各种纳米粒子的大规模合成方法的质量提供了一种强大的方法，也为定向组装微调颗粒间相互作用提供了方法，这对于持续实现单分散纳米粒子的广泛技术潜力都是至关重要的挑战。
