Synthesis of silver nanoparticles and their self-organization behavior in epoxy resin

Silver nanoparticles were chemically synthesized by means of microemulsions techniques. Their self-organization behavior, including detailed description of the mechanism, the process and the resultant structure changes, was investigated by examining the electrically conductive characteristics of silver nanoparticles/solvent suspension, silver nanoparticles/epoxy resin mixture and its cured version, respectively. For silver nanoparticles suspension, higher particle concentration was found to be unfavorable to the formation of conducting paths owing to particles aggregation. For silver/epoxy mixture, transition-like changes in conductivity as a function of temperature were observed, manifesting two-stage self-organization of the nanoparticles: one related to the formation of some texture and the other related to melting and growth of the particles. As a result, conductive networks can be established by freezing the nanoparticles aggregation at the first stage under a particle loading even lower than the percolation threshold estimated conventionally. Accordingly, curing reaction of epoxy resin should be so designed as to adequately match the self-organization process. (C) 1999 Elsevier Science Ltd. All rights reserved.