Mosaicos de cargas elétricas e grandes gradientes de potencial em superfícies dielétricas formados pela evaporação de líquidos

Abstract

This work presents a study on the charge transfer of the automatic micropipette and the glass microsyringe with the grounded and ungrounded metallic part when dripping with different liquids and also when applying different electric fields in a metallic cylinder, measured with Faraday cup and analyzing how charges can change and how the excess occur at the interface drops. The main object of study developed was the evaporation of drops, the liquid was transferred through a glass microsyringe with the grounded metallic part and deposited on polytetrafluoroethylene (PTFE) surfaces with low residual electrostatic potential. During evaporation, the Kelvin probe was used to measure changes in electrostatic potential in the droplets, which registered an increase in the positive charge in the liquid until reaching a maximum value, followed by a rapid decrease in potential and then stabilization after total evaporation of the liquid. Different solutions were evaporated, deionized water and 3% NaCℓ (sodium chloride), solutions of three different surfactants sodium dodecyl sulfate (sodium lauryl sulfate) (SDS), cetylpyridinium chloride (CPCℓ), and ether 1,1,3, 3-tetramethyl-butyl-phenyl (9.5) - polyoxyethylene (Triton X-100) and drops of different pH. Through the mapping of electrostatic potential and microscopic measurements it was possible to verify an increase in charge in the drop, and where the drop was deposited the dielectric surface became positive and the surroundings in the PTFE, negative. In addition, an electrostatic model was proposed for the evaporation of liquid droplets deposited on the PTFE surface, where the negative charges (hydroxyls; OH-) are disposed in excess at the water-air and water-PTFE interface, while the positive charges (hydrons, H3O+) are found inside the drop (bulk). It is believed that all this work can collaborate/contribute to meteorological research in the future, as there is no model or electrification process explained for drops during evaporation. Also to be able to store all this energy generated spontaneously, which may someday be an alternative energy source.