Surface properties of emulsan-analogs

The colloidal properties of emulsans formed by incubations of Acinetobacter calcoaceticus RAG-1 on different carbon sources were studied. The apparent critical micelle concentrations (CMC) of the emulsans tested ranged from 2 5 to 58 mg/dm(-1). Surface and interfacial tensions of the solutions showed little dependence on pH between 2 and 10. In contrast, increasing the pH f rom 2 to 6.5 resulted in a substantial increase in their ability to effecti vely emulsify aliphatic hydrocarbons. Hexadecane-in-water emulsions were pr epared having droplet sizes between 6 and 19 mu m. Many of the emulsions th us formed were found to be stable with respect to coalescence for several m onths. Certain structural features such as the total content of fatty acids and hydroxy fatty acids were found to have a significant effect on emulsif ying activity. The maximum emulsifying activity occurred for emulsans conta ining about 460 nmol of total fatty acid per mg of emulsan (nmol mg(-1)). E mulsifying activity also showed a maximum at about 170 mol mg(-1)-emulsan o f 2- and 3- hydroxy dodecanoic acids. For substituents having chain lengths greater than or equal to 15 carbonatoms, the emulsifying activity on hexad ecane increased with their content up to 190 nmol mg(-1). On the other hand , for substituents having chain lengths of <15 carbonatoms, the emulsifying activity on hexadecane showed no obvious effect with their content up to 2 20 nmol mg(-1). A further increase in the shorter chain length fatty acids resulted in a decrease in emulsifying activity. Hence, a substrate-specific interaction between emulsans and the dispersed phase was observed. (C) 199 9 Society of Chemical Industry.