Diverse Bubble Surface Mobility in Alcohol-Water Solutions

Previous studies have shown that the mobility of bubble surfaces in aqueous solutions can be tuned by adding different amounts of ethanol or propanol. This observation raises a question: Which types of alcohols can modulate the bubble surface mobility in aqueous solutions? To address this, we select methanol, a short-chain alcohol, and glycerol, a representative polyalcohol, for their distinct molecular structures. The mobility of bubble surfaces in aqueous solutions of these alcohols is characterized by measuring the thin liquid film drainage between an air bubble and a mica surface across a wide range of alcohol concentrations and bubble approach velocities. In methanol-water solutions, the bubble surface transitions from immobile to fully mobile as the methanol concentration increases, a behavior similar to that observed with ethanol and propanol. The critical methanol concentration required for this transition increases as the bubble approach velocity decreases. In contrast, in glycerol-water solutions, the bubble surface remains tangentially immobile across all glycerol concentrations tested. These results demonstrate that tunable bubble surface mobility is not a universal feature of the alcohol-water mixtures. Instead, it depends on the interfacial molecular structure established by specific alcohol and water molecules.