Electrical Conductivity at Surfaces of Silica Nanoparticles with Adsorbed Water at Various Relative Humidities

Abstract

Electrical conductivity of silica nanoparticles deposited on electrodes from colloidal suspension were measured under controlled relative humidity (RH). The electrical conductivity values at 1 kHz increased with increasing RH. Amounts of water adsorbed on silica nanoparticles were measured by quartz crystal microbalance (QCM) and they also increased with increasing RH. An empirical power law relation was observed between the reported surface conductivity and RH data for a silica glass. By applying this relation to the silica nanoparticles, the water film thicknesses are estimated to be from 0.08 nm to 0.23 nm. The corresponding specific surface area (SSA) becomes smaller (102 m 2 g −1) than the reported value (215 m 2 g −1), indicating aggregation of the nanoparticles. In fact, aggregated rod-like structures were observed under electron and laser scanning microscopy. The electrical conduction of deposited silica nanoparticles under various RH can be understood by surface conduction in thin water films adsorbed on the nanoparticles.

High Voltages in Sliding Water Drops

“…Our measurements and previous works suggest that the surface charge on the dry substrate decays with a characteristic time scale τ (section S2.2) on the order of 1–100 s through nonzero substrate or surface conductivity − or by neutralization through ionic species in the ambient air . To account for these surface charges in the charge balance, we can modify eq for the n th drop at position x normald Q n = [ − α c s false[ χ normalΦ + U normalD ( x ) false] + σ out n − 1 false( x false) e − normalΔ t / τ ] w d x where Δ t is the time in between two drops and σ out 0 = 0 for initially uncharged substrates.…”

Slide electrification: charging of surfaces by moving water drops

“…It is known that silicon oxide or glass show significant surface conduction at a humidity above E40%. [57][58][59] This surface conduction may lead to discharging via the back electrode, or at least to a diffusion of charge away from the area where the charges were deposited.…”

Adaptive two capacitor model to describe slide electrification in moving water drops

“…In the time between two drops, ∆t, the surface charge will gradually dissipate, e.g. through non-zero substrate or surface conductivity [32][33][34][35] or by neutralization through ionic species in the air [36]. As a first-order approximation, we assume that these processes introduce an effective surface resistance, dR on each surface element dA, leading to an exponentially decaying surface charge with characteristic decay time τ = dRc s dA.…”