Charge and Film Drainage of Colliding Oil Drops Coated with the Nonionic Surfactant C₁₂E₅

The interaction forces between colliding tetradecane drops were measured in the presence of the nonionic surfactant pentaethylene glycol monododecyl ether (C₁₂E₅). The force behavior was measured in the range of premicellar compositions of the nonionic surfactant in various salt solutions and was consistent with the presence of a surface charge even though the surfactant was nonionic in nature. The surface potential of oil drops was found to decrease with an increase in C₁₂E₅ concentration. The measured electrophoretic mobilities and ζ potentials of emulsified tetradecane drops also decreased with an increase in the C₁₂E₅ concentration. The surface potential decreased with an increase in the electrolyte at a constant C₁₂E₅ concentration, further confirming the presence of a charged oil-water interface. In addition to the charging behavior, the nonequilibrium film drainage between the tetradecane drops coated with C₁₂E₅ was also measured. In contrast to some existing experiments in the literature, it was found that oil drops coated with the nonionic surfactant were stable against coalescence, even when the drops were deformed on the order of their radii. These findings have significant implications on the stability of emulsions in food, personal care, and detergent industries.