Investigation of salts behavior at liquid–liquid interfaces

We have used molecular dynamics simulation to investigate hydrophilic– hydrophobic interfaces between calcium chloride (CaCl₂) aqueous solutions and normal hexane. The results demonstrate the increasing impact of salt concentration on the liquid–liquid interfacial tension, hence, negative adsorption of CaCl₂ according to Gibbs adsorption isotherm. Moreover, we calculated the density profiles of hexane, water, and the counter ions. The results reveal an electrical double layer near the interface and the less affinity of calcium cations toward the interface than that of chloride anions. Orientation of water molecules at the studied concentrations may result in developing a positively charged interface and, consequently, accumulation of anions close to the charged interface. Our calculations show that the interfacial width decreases by increasing salt concentration. Therefore, consistent with the calculated interfacial tension (IFT) data, aqueous salt solutions are less miscible in normal hexane at higher salt concentrations.