Effect of Oily Additives on Foamability and Foam Stability. 1. Role of Interfacial Properties

Foam tests and model experiments with sodium dodecylbenzenesulfonate solutions are performed to clarify how the foam stability and the foaminess are affected by several oils of different chemical structure. The foam tests show that 2-butyloctanol (2BO, branched alkanol) and isohexyl-neopentanoate (IHNP, branched ester) exhibit a significant antifoam activity at concentrations as low as 0.005 wt %. n-Heptanol also acts as an antifoam, but at concentrations above 0.15 wt % due to its higher solubility in the surfactant solution. The model experiments prove that the antifoam activity of pre-emulsified oils is determined primarily by the barrier to drop entry, which controls the drop emergence on the solution surface. If the entry barrier is high (e.g., n-dodecanol and silicone oil), the oil drops remain arrested in the Plateau borders during the process of foam drainage, without being able to destroy the foam. Thus branched long-chain alkanols (like 2BO) and esters (IHNP) behave as active antifoams, because ...