Conduction and Excess Charge in Silicate Glass/Air Interfaces

Abstract

The glass/air interface shows electrical properties that are unexpected for a widely used electrical insulator. The mobility of interfacial charge carriers under 80% relative humidity (RH) is 4.81 × 10 −5 m 2 s −1 V −1 , 3 orders of magnitude higher than the electrophoretic mobility of simple ions in water and less than 2 orders of magnitude lower than the electron mobility in copper metal. This allows the glass/air interface to reach the same potential as a biased contacting metal quickly. The interfacial surface resistance R increases by more than 5 orders of magnitude when the RH decreases from 80 to 2%, following an S-shaped curve with small hysteresis. Moreover, the biased surfaces store charge, as shown by Kelvin potential measurements. Applying an electric field parallel to the surface produces RH-dependent results: under low humidity, the interface behaves as expected for an ideal two-dimensional parallel-plate capacitor, while under high RH, it acquires and maintains excess negative charge, which is lost under low RH. The glass surface morphology and potential distribution change on the glass/air interface under high RH and applied potential, including the extensive elimination of nonglass contaminating particles and potential levelling. All these surprising results are explained by using a protonic-charge-transfer mechanism: mobile protons dissociated from silanol groups migrate rapidly along a field-oriented adsorbed water layer, while the matrix-bound silicate anions remain immobile. Glass may thus be classified as the ionic analogue of a topological insulator but based on structural features and charge-transfer mechanisms different from the chalcogenides that have been receiving great attention in the literature.

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.…”

Balancing charge dissipation and generation: mechanisms and strategies for achieving steady-state charge of contact electrification at interfaces of matter

“…The characteristic time of charge dissipation was less than 0.1 seconds in this case. 173 Various functional relationships between humidity and surface conduction have been reported in previous studies. Some studies reported that the surface conductivity of insulating materials increased approximately exponentially with increasing humidity.…”

“…161,165 Other studies suggested that a threshold humidity was involved for other materials. 171,173,174 Below the threshold, the surface conductivity did not increase signicantly as humidity increased; above the threshold, the surface conductivity increased drastically as humidity increased.…”

“…23,161,170 Therefore, most insulating materials (e.g., inorganic materials and polymers) showed a drastic increase in surface conductivity with increasing humidity. 161,[171][172][173][174] For example, the surface conductivity of glass was found to be about 10 À12 S , À1 below a relative humidity of 30%. Under these conditions, the glass belonged to the insulative regime.…”