Size and shape control of metal nanoparticles using dendron ligands

金属纳米粒子的物理和化学性质强烈依赖于其尺寸和形状，因此对其进行控制在基础研究和应用中都是非常重要的。我们尝试通过两种不同的系统：微流反应器和反胶束来控制粒子的大小。首先，在微流反应器系统中，合成了具有氨基焦点的1-4代聚苄基醚树枝状配体。这些树枝状配体与有机金属化合物(Pd(II)醋酸酯，Pd(OAc)2)混合在高沸点的惰性溶剂(二苯醚，bp.259℃)中，从注射器推入内径150-300μm的二氧化硅微流动反应器。采用Pd(OAc)2热分解法制备了Pd纳米粒子。在该体系中，考察了反应温度、反应器内径、流量、前驱体浓度和配位体浓度等流动参数对Pd纳米粒子的影响。得到了以下结果：(1)p…随着反应温度的升高，颗粒尺寸从2.7 nm增大到4.8 nm。(2)颗粒尺寸随线流速的增加而减小，但与体积流速无关。此外，(3)当r=1-2时，粒径最小，其中r由树枝状大分子与金属前驱体的摩尔比定义。我们还发现，在较宽的金属前驱体浓度范围内(1-27 mm)，颗粒尺寸没有变化，并保持了良好的单分散性，而在间歇式反应器中，随着前驱体浓度的增加，平均颗粒尺寸和多分散性都显著增加。其次，合成了聚苯醚树枝状聚乙二醇链，用于在有机溶剂中制备反胶束。由于亲水性/溶血性平衡(HLB值)随聚乙二醇链的长度(N)而变化，因此我们从n=6开始。然而，它不足以在反胶束中溶解水。因此，我们合成了聚乙二醇链较长的树枝状分子，n=8和11.5。研究发现，聚乙二醇链最长的树枝状分子能在甲苯反胶束中增溶水。然而，目前还不清楚这些胶束是否可以作为金属纳米颗粒的储存库。较少

Physical and chemical properties of metal nanoparticles strongly depend on their size and shape, thus their control is very important in both basic researches and applications. We have attempted to control the particle size by two different systems : microflow reactor and reversed micelle.First in the microflow reactor system, poly (benzyl ether) dendron ligands of generations 1 to 4 with an amino focal group have been synthesized. These dendron ligands were mixed with an organometallic compound (palladium (II) acetate, Pd(OAc)_2) in an inert solvent with a high boiling point (diphenyl ether, bp.259℃) and pushed out from a syringe to a silica microflow reactor with 150-300μm in inner diameter. The Pd nanoparticles were yielded by thermal decomposition of Pd (OAc)_2. In this system, effects of flow parameters, i.e. reaction temperature, inner diameter of the reactor, flow rate, concentrations ofprecursor and ligand, have been investigated. The following results were obtained : (1) The p … More article size increases from 2.7 to 4.8 nm with increasing the reaction temperature, (2) the particle size decreases with increasing linear flow rate but does not depend on the volume flow rate. Moreover, (3) the particle size shows the minimum at r=1-2where r is defined by the dendrimer to metal precursor molar ratio. We found also that the particle size does not vary in a wide concentration range of the metal precursor (1-27mM) with keeping an excellent monodispersity, while in the batch reactor, a significant increase in both the mean particle size and the polydispersity was observed with increasing the precursor concentration. This implies that the microflow reactor system is feasible for mass production of size-regulated metal nanoparticles.Second, poly (benzyl ether) dendrons attached with a polyethyleneglycol (PEG) chain at the focal point were synthesized for making reverse micelles in organic solvents. Since the hydrophil/lyophil balance (HLB) varies with the length of PEG chain(n), we started with n=6. However, it was not long enough to solubilize water in the reverse micelle. Therefore we synthesized the dendron with a longer PEG chain, n=8 and 11.5. The dendon with the longest PEG chain has been found to solubilize water in the reverse micelles in toluene. However, it is not yet clear that these micelles can work as a reservoir for metal nanoparticles. Less