Electrochemistry on Tribocharged Polymers Is Governed by the Stability of Surface Charges Rather than Charging Magnitude

Abstract

Electrically insulating objects gain a net electrical charge when brought in and out of contact. This phenomenon -triboelectricity -involves the flow of charged species, but to conclusively establish their nature has proven extremely difficult. Here, we demonstrate an almost linear relationship between a plastic sample's net negative charge and the amount of solution metal ions discharged to metallic particles, with a coefficient of proportionality linked to its electron affinity (stability of anionic fragments). The maximum magnitude of reductive redox work is also material-dependent: metallic particles grow to a larger extent over charged dielectrics that yield stable cationic fragments (smaller ionization energy). Importantly, the extent to which the sample can act as electron source greatly exceeds the net charging measured in a Faraday pail/electrometer set up, which brings direct evidence of triboeletricity being a mosaic of positive and negative charges rather than a homogenous ensemble, and defines for the first time their quantitative scope in electrochemistry.

Irreproducibility in the triboelectric charging of insulators: evidence of a non-monotonic charge versus contact time relationship

“…Surface mechanical properties are known to affect material transfer, 5,26 and hence the charge exchange between two polymers. Further, material-specific ion stabilities 22 contribute to define the mosaic pattern of positive and negative domains that sum up to give a tribocharged sample its net (measurable) charge. Faraday pail charge measurements of identical materials are arguably the simplest laboratory model for the kinetic analysis of charge build-up.…”

“…Pressing two identical polymers together, followed by separation, causes transfer of charged material. 18,20,22 A small and unavoidable asymmetry in the applied mechanical force, and/or a small difference in hardness and adhesion (Fig. S1, ESI †), 5 leads to triboelectrification even of identical materials.…”

“…In the discussion that follows we specifically focus on the negatively charged sample, as this is expected to mediate the reduction of larger amounts of reducible species 39 and find potential applications in electrochemistry and catalysis. 22,30 Charge versus time curves for the positive sample are in Fig. S2, ESI †.…”

“…4. The electrification of identical materials involves the movement of ionic polymer fragments, 7,22 and the partition of these fragments between the two PTFE surfaces is clearly asymmetric 3). Upon contact and separation, one PTFE sample becomes positive and the other negative.…”

“…[11][12][13][14][15][16][17] Through Kelvin probe force microscopy (KPFM) [18][19][20] and Faraday pail measurements, 21 static charges present on a surface can be accurately mapped and measured. A number of studies have used these types of measurements to highlight the complexity of the triboelectrification process -ionization energy, electron affinity, 22,23 moisture, 24,25 adhesion, 5 hardness, 5,26 contact force, 19 gas dissolution, 27 as well as the exact surface chemistry 23 -all play a role in it. A correct and complete understanding of the process is still lacking.…”