Fabrication of nanoparticle assemblies with a controlled number of constituent nanoparticles by membrane emulsification using anodic porous alumina

Abstract

Nanoparticle assemblies with a controlled number of constituent nanoparticles were fabricated by membrane emulsification using an aqueous solution containing silica or Au nanoparticles as dispersed phases. For membrane emulsification, ideally ordered anodic porous alumina with extremely uniform-sized pores was used as an emulsification membrane to control the droplet size precisely. The nanoparticle assemblies were formed when droplets containing nanoparticles obtained by membrane emulsification dried up through solubilization in the continuous phase. In this process, the number of constituent nanoparticles in the assemblies could be controlled by changing the concentration of nanoparticles in the dispersed phase and the pore size of anodic porous alumina. Optimizing the concentration of nanoparticles in the dispersed phase and the pore size of anodic porous alumina also confirmed the preferential formation of dimers and trimers of nanoparticles. The Au nanoparticle assemblies obtained by this process could be applied to substrates for enhanced Raman scattering because of the enhanced photoelectric field formed between Au particles.