Biomimetic strategies for the control of size, shape and self-organization of nanoparticles

Abstract

An unusual phase diagram is presented. It is composed of copper(II) bis(2-ethylhexyl) sulfosuccinate Cu(AOT) 2-isooctane-water. Keeping the concentration of the Cu(AOT) 2-isooctane solution constant, increasing in the amount of water induces various phase transitions. At low water content, spherical and cylindrical reverse micelles are formed. By increasing the water content, a bicontinuous system appears. Further addition of water leads to the formation of planar and spherulite type lamellae. As more water is added only spherulites remain in the phase. Still further addition of water leads to a reappearance of an interconnected network and then reverse micelles. Syntheses performed in the various parts of the phase diagram show that the use of colloidal assemblies as templates favors the control of the shape of nanoparticles. Cylindrical metallic copper particles having the same size can be obtained in various parts of the phase diagram when the template is made of interconnected cylinders. A very low amount of cylinders (13%) is formed when the synthesis is performed in cylindrical reverse micelles. When the colloidal self-assembly is a mixture of several phases, various types of shapes can be obtained. In some cases, the polydispersity in size is so low that metallic particles are able to self-assemble in a hexagonal network. Multilayers can be observed and are arranged in a face centered cubic structure.