Magnetic Field Effects on Aqueous Anionic and Cationic Surfactant Solutions Part I: Water Evaporation

Abstract

Static magnetic field (0.5 T) effects on water evaporation rate from anionic Sodium Dodecyl Sulfate (SDS) and cationic Dodecyl Trimethyl ammonium Bromide (DoTAB) 1 mM solutions were studied at room temperature and humidity for up to several hours. Keeping in mind possible practical application of the effects the experiments were intentionally carried out in a common laboratory environment and not in any sophisticated conditions. The evaporation of water from Magnetic Field (MF) treated and untreated samples were carried out simultaneously in the same environment. Although the quantitative differences in the evaporated amounts of water between MF treated and untreated samples changed from run to run, the qualitative MF effects were always reproducible. Therefore, it is believed that the observed changes are significant. It was found that the MF affects evaporation rate of water from solutions of both surfactants causing increase in the evaporated water amount in comparison to that of MF untreated sample. Prior to MF experiments first the water evaporation rate from the untreated surfactants solutions was studied. From the MF-untreated anionic surfactant solution water evaporated slower than from pure water, while from the cationic one water evaporated faster than from pure water. This difference was explained taking into account the properties of the polar (ionic) head of the surfactants, i.e. their size, ability to hydrogen bonding formation with water molecules, and the reduction of water surface tension. The MF treatment caused an increase in the evaporated water amount from both surfactants. However, a greater effect was observed for cationic DoTAB. Because the hydrocarbon tail in both surfactants is the same (C12) the observed differences were assigned to the differences in their ionic heads. Gibbs adsorption equation and Lorentz force in the gradient MF were applied to explain the differences.