Size and shape control of metal nanoparticles using dendron ligands

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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