Modulation of Surface Charge by Mediating Surface Chemical Structures in Nonpolar Solvents with Nonionic Surfactant Used as Charge Additives

One of the major challenges in controlling the colloidal stability in nonpolar solvents concerns their surface charging strength. By tuning surface chemical structures in nonpolar solvents, the surface charge can be modulated with nonionic surfactants used as charge additives. In this study, various self-assembled monolayers (SAMs) were coated onto specific surfaces and nanoparticles to obtain different chemical structures. X-ray photoelectron spectroscopy (XPS) and atomic force microscope (AFM) measurements were used to quantify surface chemical structures, whereas dynamic adsorption experiments and molecular dynamics (MD) simulation were utilized to study the influence of these structures on surfactant adsorption behavior. Surface charging optimization was achieved by mediating the concentration of electron acceptors and donors, which is reflected as matching the alkyl length of SAMs with an appropriate concentration of hydroxyl group on the surfaces. The charging strength of particles decreased above a certain surfactant concentration, which is attributed to the competition between surfactant adsorption stability and charge neutralization effect generated via the disproportionation process.

Automated summary

Controlling the surface charging strength in nonpolar solvents is a major challenge when it comes to colloidal stability. By tuning surface chemical structures and using nonionic surfactants as charge additives, the surface charge can be modulated. Various self-assembled monolayers were coated onto specific surfaces and nanoparticles in this study to obtain different chemical structures, with techniques like XPS and AFM used to quantify these structures. Optimizing surface charging was achieved by adjusting the concentration of electron acceptors and donors, while the strength of particle charging decreased above a certain surfactant concentration due to competition between adsorption stability and charge neutralization effect.