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The ability to retain localized charges at the surface or interface of dielectric materials is a universal property that applies to many different fields such as tribocharging, charge nanopatterning, nanoxerography, etc. Once the surface is charged, its stability and subsequent discharging rate will determine the potential applications of a given system. This decay rate is properly defined by the macroscopic equations which depend on dielectric constants and conductivities of the two media. Here, we derive the equations to model the decay of charge distributions localized at the surface/interface of materials and solve them avoiding additional approximations made so far. Addressing the problem in the Fourier space, we arrive to a compact generic equation which provides a useful tool to determine both the bulk and surface conductivities of a material. Furthermore, we show that Kelvin Probe Force Microscopy (KPFM) is a particularly suited method to exploit this tool. Monitoring the charge decay of previously injected charge patches on silicon dioxide (SiO 2), together with an appropriated data analysis, we verify the behavior predicted by our equations. This allows us to characterize the surface and bulk conductivities of SiO 2 layers as well as its dependence with the relative humidity. [Display omitted] • Surface charging of dielectric materials is a universal property. • The dependence of the surface charge decay rate with the system geometry is established. • Surface and bulk conductivities are obtained with Kelvin probe force microscopy. [ABSTRACT FROM AUTHOR]

The abnormal stability of bulk nanobubbles has attracted substantial attention from academia and industry since classical Epstein–Plesset theory predicts that gas bubbles cannot keep stable thermodynamic equilibrium spontaneously. The dual nature of ionic surfactants, acting simultaneously as charge carriers and attenuators of surface tension at the gas–liquid interface, enables them to play a unique role in bulk nanobubble stabilization. Herein the stability of bulk nanobubbles in anionic, cationic and nonionic surfactant solutions over a wide range of concentration is studied. Experimental results show that different kinds of surfactant molecules are involved in the nucleation and stabilization of bulk nanobubbles in different ways. We demonstrate that the accumulation of net charges carried by surfactant ions at the interface is predominantly responsible for stabilizing nanobubbles, instead of the reduction of surface tension. With theoretical calculations, we further quantify the coupling action of interfacial tension and surface charge on the stable equilibrium state of bulk nanobubbles. The result illustrates that the interfacial tension and the degree of gas saturation together determine the upper limit of the bubble size that can exist stably. Our study identifies a route to explore the intrinsic mechanism of bulk nanobubble's stability. [Display omitted] • Stability of bulk nanobubbles in ionic and nonionic surfactant solutions is studied. • Surfactant molecules are involved in the nucleation and stabilization of nanobubbles. • Accumulation of net charges is predominantly responsible for stabilizing nanobubbles. • Coupling action of interfacial tension and surface charge is revealed. • Interfacial tension and gas supersaturation together determine the upper bound size. [ABSTRACT FROM AUTHOR]