Surface Charge Properties of Nanoparticle: Size Dependency and Boundary Effect

Surface charge properties of nanoparticles play an important role in many applications, such as drug delivery, cellular uptake and their separation. Surface charge properties of silica nanoparticles are investigated as functions of particle’s size, solution properties including pH and background salt concentration, and separation distance from a flat silica surface using a multi-ion charge-regulation model. In contrast to most previous studies utilizing constant surface charges regardless of the local solution properties, surface chemical reactions in the presence of multiple ionic species are considered in this study. The obtained results agree with experimental data available from the literature. Results show that the magnitude of nanoparticle’s surface charge density increases with its size due to the curvature effect and the presence of the nearby boundary induces spatially non-uniform surface charge around the nanoparticle as while decreasing the kh, the degree of nonhomogeneous distribution increases. Due to the surface chemical reactions, both pH and background salt concentration significantly affect the charge properties of silica nanoparticles.