Construction of insulating layers on conductive nickel-plated core particles by thermal fusion of heterocoagulated polymer shell particles

Abstract

In this study, we developed a method for fabricating conductive particles with an insulating layer on the surface, which can be applied to anisotropic conductive films. Core-shell particles were prepared from conductive nickel-plated core particles and positively charged polystyrene (PSt) shell particles carrying phosphonium groups on their surface by the heterocoagulation technique. The effect of alkyl chain lengths (ethyl, n-butyl, and n-octyl) of (4-vinylbenzyl)trialkylphosphonium chloride on the interfacial properties was investigated by surface tension measurement. Monodisperse PSt shell particles with a controlled particle size were successfully synthesized by emulsifier-free emulsion polymerization of styrene, (4-vinylbenzyl)triethylphosphonium chloride, and n-butyl acrylate. The effects of stirring time, temperature, NaCl concentration, and PSt shell particle concentration on heterocoagulation between the nickel-plated core particles and PSt shell particles were investigated. Uniform core-shell particles with a coverage of 60% could be prepared even though the heterocoagulation temperature was below the glass transition temperature and the NaCl concentration was below the critical coagulation concentration of the PSt shell particles. When the core-shell particles obtained through the heterocoagulation process were heated above the glass transition temperature of the shell particles for 6 h, a smooth polymeric insulating layer with melted shell particles was successfully formed on the surface of the nickel-plated core particles.