Phase and Dispersion Stability of Silver Nanocolloids for Nanoparticle-Chemisorption Printing

Here we investigated the unique phase and dispersion characteristics of alkylamine/alkylacid encapsulated silver nanocolloids (AgNCs) that allowed the production of ultrafine metal wiring using the nanoparticle chemisorption printing technique. We found that a polar methanol component, which was unintentionally involved during the synthesis of the AgNCs, promoted the instability of the colloidal phase and slightly accelerated the flocculation of the silver nanoparticles (AgNPs). We also investigated ternary phase diagram of a mixed solvent system of octane/butanol/methanol in the absence of AgNPs. The phase separation was observed at relatively large methanol content, and the feature was closely associated with the deterioration of AgNCs due to phase separation. In the unseparated AgNCs, the methanol component accelerated the self-aggregation of AgNPs, eventually triggering the phase separation that took place at lower methanol content as compared to the pure mixed-solvent system. Furthermore, the self-aggregation considerably affected the conductivity of the printed silver wires without undergoing the annealing process. We discuss that the compatibility of encapsulating ligands with polar/nonpolar solvent molecules is the key to understand the instability of AgNCs.