technique as a function of the alcohol activity for butanol solutions. The arrow indicates the limit of solubility. (From Ref. 80.)

Our results also proved the correlation between foamability and surface tension gradient for aqueous nonionic surfactant solutions. Foam formation was estimated from a dynamic surface tension using the maximum bubble pressure method, and foam stability was estimated from a transfer distance of lamella using a laminometer. Laminometer measurements were made using the Du Noüy ring method [1, 78, 96]. Force profile during the expansion of lamella was monitored using an electronic-balance with expansion rate at 0.1 mm sec−1. The degree of elongation of lamella, Llamellae, was defined as follows.