Synthesis of silica Janus nanoparticles by buoyancy effect-induced desymmetrization process and their placement at the PS/PMMA interface

This work presents a unique desymmetrization method to produce a high quantity of Janus nanoparticles (JNPs) using dual-phase oil (melted wax)/water system. The four-stage process includes fixing, primary modification, releasing, and secondary modification. Unlike other works, dispersed hydrophilic nanoparticles were forced to be placed at oil/water interface using an upward water stream formed by buoyancy effects due to the applied heat to the bottom of the container. This eliminated some significant deficiencies of common desymmetrization processes which apply oil (melted wax)/water Pickering emulsion systems, e.g., the coalescence of melted /solidified wax droplets and high cost. The best effect of heat-driven buoyancy flow was ensured using saturation theory. In order to induce asymmetrical surface properties to the applied nanoparticles, (3-aminopropyl)triethoxysilane and hexadecyltrimethoxysilane were used in primary and secondary modification stages, respectively. Produced JNPs were characterized using FTIR, thermogravimetric analysis (TGA), and energy-dispersive X-ray spectroscopy (EDX) tests in order to confirm the attachment of modifier molecules on the surface of the applied nanoparticles. Furthermore, TGA results were used to calculate three-phase contact angle (beta) as an important parameter dictating the asymmetric properties of Janus nanoparticles. Also, a dichloromethane/water mixture was used to demonstrate the differences of Janus nanoparticles with similar uniformly modified nanoparticles. Furthermore, using polystyrene/poly(methyl methacrylate) blend, it was shown that produced Janus nanoparticles tend to be placed at the interface while their corresponding uniformly modified nanoparticles stay in polystyrene or poly(methyl methacrylate) phase.