Electrostatics is an old area of scientific research that lagged behind most other areas of natural sciences and especially chemistry and physics, during the 20th century. The role of interfaces as important sites for electric charge accumulation or exchange is well established in solid-solid, liquid-liquid and liquid-solid systems. However, this is not the case for gas-liquid or gas-solid interfaces. Water with excess charge is the outcome of many different events triggered by electric fields or by interfacial phenomena that produce non-electro-neutral water, either liquid, solid or vapor, due to excess H<sup>+</sup> or OH<sup>–</sup>concentration. As interfaces are recognized sites for electrification, we used a very simple apparatus to measure the electrostatic charge during phase transition at liquid-gas and solid-gas interfaces. The experiment consists on recording the electrostatic charge of a water drop on polytetrafluoroethylene (PTFE) during evaporation. This is simply done with a Kelvin probe and an optical microscope. Well-controlled experiments as shown in the figure attached reveal that when a drop of water is positioned on top of PTFE surface the electrostatic potential remains pretty stable until the drop has reached roughly half of its volume. After that, the electrostatic potential starts to increase significantly reaching high positive potentials + 12 V and high potential gradients. Finally, there is a slight electrostatic potential decreasing, reaching a plateau when there is no more water on PTFE. This equilibrium electrostatic potential is very stable and did no change even after 21 days of measurement. Experiments done in microscale with a Kelvin Probe Force Microscopy confirms the macroscopic results. At this point we speculate that the asymmetric partitioning of hydroxide and hydronium ions from water autolysis play a key role on the spontaneous charge build-up on dielectric surfaces by the evaporation of water and considering the ubiquitously of water formation/evaporation on many systems, this discovery may be extremely relevant from atmospheric sciences to ESD control in electronic industry.

Spontaneous mosaic of charges and high potential gradients on dielectric surfaces formed by evaporating liquid drops

Macromolecular Chemistry: The Second Century

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ACS Spring 2020 National Meeting & Expo

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.