Interpretation of Electrostatic Self-Potential Measurements Using Interface-Trapped Microspheres with Surface Heterogeneity

Electrostatic self-potentials of individual particles trapped at an oil-water interface were determined, and the effects of surface chemical nonuniformity on heterogeneous self-potentials and equilibrium microstructures were investigated. Direct measurement of the pair interactions and the self-potentials of polystyrene microspheres were performed using optical laser tweezers. The individual particles had different self-potentials even when they possessed the same surface functionalities. Atomic force microscopy measurements elucidated the relationship between nonuniform surface charge distribution and heterogeneity and magnitude of self-potentials. Monte Carlo simulations demonstrated that self-potential heterogeneity led to the formation of more melted microstructures that showed excellent consistency with experiments.