Hybrid Nanoparticles for Enhanced Assembly at Oil-Water Interfaces: A CO2-Assisted Functionalization Approach

Abstract This research presents a novel approach to enhance the assembly of nanoparticles (NPs) at the oil-water interfaces through hybrid functionalization. Silica NPs were initially functionalized with two silanes, which improved their colloidal stability at high temperature and salinity environment. However, at neutral pH, the NPs failed to assemble at the interface due to particle-particle repulsive interactions. To address this limitation, a third functionalization step was introduced, involving the incorporation of stearic acid into the NP surface via an interfacial assembly method facilitated by CO2 bubbling, which enabled efficient dispersion of the particles and provided additional binding sites for the stearic acid molecules. The resulting hybrid NPs exhibited enhanced hydrophobicity, leading to improved assembly at the oil-water interface. Interfacial tension measurements revealed a significant reduction in interfacial tension, comparable to values obtained with molecular surfactants. Additionally, the hybrid NPs displayed increased affinity towards the interface, driven by hydrophobic interactions. Contact angle measurements confirmed the improved hydrophobicity of the hybrid NPs, showing a 30-degree reduction in contact angle compared to the original NPs. Transmission Electron Microscopy (TEM) and X-Ray Photoelectron Spectroscopy (XPS) analyses validated the successful incorporation of stearic acid onto the NP surface. Thermogravimetric Analysis (TGA) showed a notable increase in organic content, indicating the attachment of stearic acid molecules. These findings demonstrate the effectiveness of the proposed hybrid functionalization strategy in overcoming the limitations of traditional NP-based systems. The development of these hybrid NPs opens up opportunities for exploiting them in complex environments, such as those encountered in industrial processes, biomedical applications, and environmental remediation. By leveraging the unique properties of these hybrid NPs, researchers can design and engineer novel systems capable of manipulating fluid-fluid interfaces, enabling breakthroughs in fields like emulsion stabilization, microfluidics, and nanotechnology.