Abstract
A surfactant is considered efficient when it possesses strong hydrophobicity (saturation concentration of singly dispersed solute in water is small) and also strong lipophobicity (saturation concentration of singly dispersed solute in hydrocarbon is small). Hydrophobicity is strongly dependent on alkyl chain length of the surfactant, while lipophobicity is mainly related to the length and type of hydrophile group. Lipophobicity, i.e., decrease in saturation concentration of singly dispersed solute in hydrocarbons in equilibrium with water phase, is an important property of amphiphiles. The method for measuring lipophobicity should be modified according to solution behavior of surfactant with particular attention to sample concentration when lipophobicity is quite high.
The characteristic properties of nonionic surfactants with hydroxyl groups as the hydrophilic moiety including alkyl glyceryl ethers and alkyl monoglycerides were studied and compared with those of nonionic surfactants having oxyethylene groups. The lipophobicity after introducing an oligo (oxyethylene) group into nonionic surfactants was found to increase by 2.5 times that of an oxyethylene group, or the secondary hydroxyl group, -CH (OH) -, and 4.6 times that of an oxyethylene group. Subsequent to transition from -O- (ether) to -COO- (ester), lipophobicity increased to 5 times as much. The lipophobicity of hexa (oxyethylene) dodecyl ether and monoglyceryl α-dodecyl ether were noted to be essentially the same; the former was water-soluble and the latter, oil-soluble at 25°C. Nonionic surfactants with hydroxyl groups thus not only have strong lipophobicity but are oil-soluble.
Highly lipophobic surfactants should thus be quite effective in a hydrocarbon-rich system or one with aromatic hydrocarbons. Glycolipids or polyglycerol nonionic amphiphiles should prove useful as solubilizers, emulsifiers and detergents owing to their high lipophobicity and insensitivity to temperature.
