Study of influence of salt additives on the electrical percolation phenomenon in AOT reverse microemulsions

Abstract Microemulsions are self-aggregating systems that can be used as artificial models to study processes that occur in biological systems such as the transport of substances in the body and the charge transfer in neurons. Additionally, the environment of life in living organisms is mainly water, or more precisely, aqueous solutions of salts. Therefore, the study of the influence of different salt additives on the electrical percolation threshold in reverse microemulsions is topical. Our aim was to study the process of water-induced and temperature-induced electrical percolation in reverse microemulsions prepared by dissolving of the anionic surfactant sodium bis(2-ethylhexyl) sulfosuccinate (AOT) in n -decane in the presence of additives of different salts in the water droplets or dispersion phase of the microemulsions. To reveal how differences in both ion charge density and kosmotropic-chaotropic properties of salts ions affect the inhibition of electrical percolation phenomenon in reverse microemulsions was also the purpose of the proposed research. It was found that electrical percolation in AOT reverse microemulsions occurs at a relatively higher value of water/surfactant molar ratio (W) upon the addition of aqueous solutions of salts than in the case of pure water. Water-induced electrical conductivity percolation is most suppressed by salts containing both ions with high charge density values, i.e. modification of water droplets with lithium fluoride causes complete quenching of electrical percolation. It was found that electrical percolation in microemulsions with a fixed value of W takes place at relatively higher temperatures in the presence of kosmotropic and chaotropic salt additives in the water pockets of reverse microemulsions compared to microemulsions without salt additives. In the temperature-induced percolation process, the suppression of electrical conductivity percolation or its complete quenching is mainly determined by the kosmotropic or chaotropic nature of an added ions, i.e. potassium ions in conjunction with both kosmotropic and chaotropic anions, e.g. potassium fluoride and perchlorate, strongly suppress the percolation process. In contrast, sodium ions show a suppressive effect only in conjunction with strong chaotropic anions, i.e. bromide, iodide and perchlorate ions. The results may introduce a certain contribution to the study of possible mechanisms of electrical conductivity in reverse microemulsions modified with aqueous solutions of salts.