Nonionic lactose and lactitol based surfactants: comparison of some physico-chemical properties

The octyl (C8), dodecyl (C12) and hexadecyl (C16) mono-esters of lactose and lactitol have been synthesized. The lactose derivatives are a mixture of both anomers of two mono-esters while the lactitol derivatives are a mixture of both anomers of three monoesters. Generally, lactose and lactitol surfactants of equivalent chain length exhibited very similar physico-chemical properties. All six surfactants displayed thermotropic transitions of solid to smectic (A(d)) to isotropic liquid as the temperature was raised. Concentration gradient experiments indicated that for the C8 and C12 surfactants the lyotropic transitions were micellar (L-1) to hexagonal (H-1) to lamellar (L-alpha) as the surfactant concentration increased relative to water. For the C16 surfactants the lyotropic transitions were micellar (L-1) to lamellar (L-alpha). Air-water surface tension curves have been employed to determine the critical micelle concentration (cmc), free energy of micellization, minimum area per surfactant molecule at the air-water interface, surface tension at the cmc and minimum surface tension for each surfactant. Interfacial tensions for aqueous surfactant solutions in contact with hexadecane and triolein have been measured. The interfacial tensions suggested that, above the cmc, the lactose and lactitol mono-esters would be good emulsifiers. Ross-Miles foam heights have shown that the C8 and C12 lactose and lactitol surfactants form foams with good height and stability above the cmc. All six surfactants have been found to be relatively poor cotton wetting agents. (C) 1998 Elsevier Science B.V.