Magnetic Field Effects on Aqueous Anionic and Cationic Surfactant Solutions Part II: Surface Tension

Magnetic Field (MF) effects on water and dispersed systems have been studied for more than half of century. However, so far there is no complete understanding of the observed changes in the properties of studied systems if it is solely based on the classical theories of magnetic field action. In Part I of this paper we presented results of MF influence on the evaporation rate of aqueous solutions of anionic surfactant Sodium Dodecyl Sulphate (SDS) and cationic one Dodecyl Trimethylammonium Bromide (DoTAB). In this paper static magnetic field effects on the surface tension of the above-mentioned surfactants are presented. The concentrations of the solutions used were both below and above their Critical Micelle Concentration (CMC). The solutions were under the MF action for 60 min in a closed vessel and were stirred by hand every 15 min. Previously it was found that the surface tension of pure water (distilled in a quartz apparatus) decreased by 2.1 mN/m after similar the MF treatment. Moreover, the memory effect lasted longer than 60 min. In case of the surfactant solutions the surface tension changed depending both on the kind of surfactant and its concentration. Bigger changes were observed for cationic DoTAB. In the solutions below their CMC the surface tension was lower after MF treatment. However, the surface tension of DoTAB solution at CMC increased several mN/m after the MF treatment. In the solutions concentrated above the CMC, respectively, the MF effects were practically vanishing. The observed changes are discussed in detail considering the structure of the surfactant adsorbed layers and acceleration force acting on the ions which was calculated from the Lorentz equation. To our knowledge, such results are published in the literature for the first time and they should be considered as preliminary ones. More systematic experiments are needed to better understand the observed changes.