College of Chemistry and Chemical Engineering, State Key Laboratory of Chemo/Biosensing and Chemometrics, Hunan University, Changsha, China.
J Chromatogr A. 2011 Jun 24;1218(25):3823-9. doi: 10.1016/j.chroma.2011.04.038. Epub 2011 Apr 20.
The experimental conditions necessary for the synthesis of well-defined nanoparticles are often difficult to control. There is thus a compelling need for post-synthesis separation of nanoparticles polydispersed in size and shape. We demonstrate here both theoretically and experimentally that gold nanorods with diverse aspect ratios can be separated using density gradient centrifugation. By analysing the force balance of a Brownian rod falling in a Stokes flow, we derive a rigorous and predictive model that reveals the quantitative dependency of the nanorod sedimentation rates on their mass and shape. The calculations show that while mass dependency is still the dominating factor during centrifugation, the shape factor is not insignificant. Relatively heavier but long and thin rods could sediment slower than certain size of lighter spheres, and some rods and spheres with different masses and shapes may never be separated. This mass and shape dependency is exploited to separate as-prepared gold nanorod colloids by sucrose gradient centrifugation. Two layers of nanorods with narrow aspect-ratio distributions are obtained.
用于合成具有明确结构的纳米粒子的实验条件往往难以控制。因此，迫切需要对尺寸和形状多分散的纳米粒子进行合成后的分离。我们在这里从理论和实验两方面证明，具有不同纵横比的金纳米棒可以使用密度梯度离心法进行分离。通过分析在斯托克斯流中下降的布朗棒的力平衡，我们推导出一个严格且可预测的模型，揭示了纳米棒沉降速率对其质量和形状的定量依赖性。计算表明，虽然在离心过程中质量依赖性仍然是主要因素，但形状因子并非不重要。相对较重但又长又细的棒可能比某些尺寸的较轻球体沉降得更慢，而某些具有不同质量和形状的棒和球体可能永远无法分离。这种质量和形状的依赖性被用来通过蔗糖梯度离心法分离制备好的金纳米棒胶体。得到了具有较窄纵横比分布的两层纳米棒。
