pH-Dependent Electrochemomechanical Transition of Hydrophobe-Water Interface

In this article, we have studied the curvature transition of hydrophobe-water interface. This transition has been observed to take place from curved-to-flattened in extreme alkaline conditions. An analytical model involving the charging-induced electrochemomechanical changes has been developed to qualitatively explain such transitions of oil-water interfaces. Two types of studies have been conducted for this work: one with liquid-liquid interface and another with solid-liquid interface, respectively. The study done with liquid-liquid interface involved the use of commercially available mustard oil that was poured over the liquids of varying pH. Further investigations done with solid-liquid interface showed the abrupt transition of the sessile drop's shape beyond a certain pH, when the drop was put on a glass slide smeared with wax. Thus, we have successfully demonstrated that the pH range of the liquids can be determined by using very simple and easily available household materials like mustard oil and wax. The detected pH range was unity (range: 11.0-12.0) in our work. It would help the researchers to determine whether a given liquid has a pH greater than or less than a certain value, depending on the choice of the oil/hydrophobic surface, just by visual inspection with no sophisticated instruments required and minimum costs incurred.