Many reports associate electrostatic charge in dielectrics with water, either bulk, finely dispersed in aerosol or as atmospheric vapor. Two widespread but currently controversial assumptions relevant to this topic are the prevalence of electroneutrality and the passive role of water in electrical phenomena, dissipating charge due to its significant electrical conductivity. Early reports from Faraday, Kelvin and their contemporaries also point towards an active role of water as an electrifying agent. Unfortunately, these have been largely ignored or treated as scattered pieces of scientific curiosity, for over a century. New trends in this area have been developing since the late 1990s, due to a number of findings leading to radically new ideas. These derive from the experimental demonstration of widespread occurrence of non-electroneutral water and from charge partition associated with a number of interfacial phenomena, even in electrically shielded environments within grounded enclosures. This is an account on the formation and persistence of electrified water in various natural or anthropic environments, followed by experimental results obtained under well-defined conditions that are revealing different mechanisms for the role of water in charge acquisition and dissipation in dielectrics.

Electrostatic phenomena were discovered long ago but their interpretation according to well-established atomic-molecular theory is still lacking. As a result, electrostatic phenomena are often irreproducible and uncontrolled, causing serious practical problems. Highly reproducible recent experimental results on electrostatic charging from this and other laboratories are reviewed in this work, together with a description of the relevant but not so usual Kelvin probe and Faraday cup techniques. These results support a new model for electrostatic charging of dielectrics and insulated metals, based on the role of moist atmosphere as a charge reservoir.

O excesso de cargas induzidas em papel, sob um potencial eletrostático foi determinado utilizando-se o método de Kelvin. Os resultados mostraram que o papel, sob um potencial elétrico positivo, acumula excesso de cargas negativas que são dissipadas quando o potencial elétrico é reduzido à zero. As velocidades de eletrização e re-neutralização do papel mostraram-se fortemente dependentes da umidade atmosférica e são interpretadas de acordo com um novo modelo para a eletrificação de isolantes, que é baseado no efeito do potencial elétrico sobre o potencial eletroquímico (µi = µi° + RTln a + zFV) dos íons H(H2O)n+ e OH(H2O)n- existentes na água adsorvida nos isolantes. O modelo é capaz de explicar os resultados experimentais apresentados neste trabalho, bem como outros fenômenos eletrostáticos.

Excess electrostatic charge induction on paper under an electrostatic potential, at different relative humidity (RH) values, was measured using a Kelvin electrostatic voltmeter set-up. Results show that samples under a positive potential accumulate excess negative charges, which are dissipated when the potential is brought down to zero. Rates of charge accumulation and dissipation over the samples are equal under constant RH and both rates decrease markedly at lower RH values. These results are interpreted using a new model for the electrification of insulators, based on the effect of the electric potential on the electrochemical potential (µi=µi° + RTln a + zFV) of H(H2O)n+ and OH(H2O)n- ions within water adsorbed on insulators. Rates of paper electrification and re-neutralization are thus strongly dependent on the amount of water in the atmosphere. This model explains the experimental results presented in this work and also a number of hitherto unexplained reports on electrostatic phenomena.