Self-Assembly of Matchstick-Shaped Inorganic Nano-Surfactants with Controlled Surface Amphiphilicity

Abstract

Molecular and nanoscale amphiphiles have been extensively studied as building blocks for organizing macroscopic matter through specific and local interactions. Among various amphiphiles, inorganic Janus nanoparticles have attracted a lot of attention owing to their ability to impart multifunctionalities, although the programmability to achieve complicated self-assembly remains a challenge. Here, we synthesized matchstick-shaped Janus nano-surfactants that mimic organic surfactant molecules and studied their programmable self-assembly. High amphiphilicity was achieved through the hard-soft acid-base-based ligand-exchange reaction with strong selectivity on the surface of nano-matchsticks consisting of Ag2S heads and CdS stems. The obtained nano-surfactants spontaneously assembled into diverse ordered structures such as lamellar, curved, wrinkled, cylindrical, and micellar structures depending on the vertical asymmetry and the interfacial tension controlled by their geometry and surface ligands. The correlation between the phase selectivity of suprastructures and the characteristics of nano-surfactants is discussed. This study realized the molecular amphiphile-like programmability of inorganic Janus nanostructures in self-assembly with the precise control on the surface chemistry.