aDepartment of Applied Surface Chemistry, Chalmers University of Technology,
SE-412 96 Göteborg, Sweden bCompetence Centre for Catalysis, Chalmers University of Technology,
SE-412 96 Göteborg, Sweden cPhysical Chemistry, Lund University
SE-221 00 Lund, Sweden
Nanostructured noble metals are of interest, since their physiochemical properties have a flora of applications in fields as diverse as photovoltaics, catalysis, electronic and magnetic devices etc. A range of physical and chemical methods has been utilized to prepare nanosized noble metals, and several of these are based on the use of a structure-directing template. Among the wet-chemical methods the ones based on the use of self-assembled amphiphilic templates have proven to be particularly successful in the preparation of nanostructured noble metals. Hexagonal and cubic liquid crystalline templates have proven useful for the synthesis of mesoporous materials of both oxides and noble metals1-3. Qi et al4 have showed that a lamellar liquid crystalline phase consisting of C12E4 surfactants and water can be used to produce silver nanoparticles with a narrow size distribution.
In this work a flexible method of preparing and macroscopically aligning nanoparticles of crystalline silver into millimeter long fibers is presented. The approach utilizes the dual functionality of a reverse hexagonal liquid crystalline template containing a built-in reducing agent facing the aqueous domain. The method is advantageous in that its slow kinetics allows for a thorough introduction of a silver salt into the liquid crystal before the reduction takes place, allowing for an efficient loading of the template and a retained mesoscopic ordering as evidenced by SAXS. It was confirmed by 1H-NMR that the oxyethylene groups of the amphiphilic polymer reduce the silver ions while being oxidized to aldehydes. The silver nanoparticles are monodisperse and in the same size range as the diameter of the aqueous domain of the liquid crystal (4 nm) further supporting that the silver particles form inside the liquid crystal. TEM images confirm the macroscopic alignment of silver nanoparticles into fibrils and the packing of fibrils into millimeter long fibers. The diameter of the fibrils and fibers ranges from 30 nm to several hundreds of micrometers. Electron diffraction analysis of a collection of silver nanoparticles confirms their crystallinity as three diffraction rings could be indexed to the face centered cubic structure of silver.