Brij 30 Induced Transition of Rodlike Micelles to Wormlike Micelles and Gels in the Imidazole Ionic Liquid Surfactants: The Alkyl Chain Length Effect

The effect of the hydrocarbon chain length of ionic liquid surfactants 1-hexadecyl-3-alkyl imidazolium bromide [C₁₆imC_n]Br (n = 1–16) on their aggregation behavior with polyoxyethylene lauryl ether (Brij 30) in aqueous solution was inspected. The rheological behavior, thermal properties, and microstructures of the different samples were studied using freeze-fractured electron microscopy. The interactions between [C₁₆imC_n]Br and Brij 30 were studied using nuclear magnetic resonance spectroscopy and theoretical simulation. With the addition of Brij 30, the rodlike micelles of [C₁₆imC_n]Br (n = 1, 2, 4, and 6) transition into wormlike micelles. The effects of the molar ratio of Brij 30 and [C₁₆imC_n]Br and the hydrocarbon chain length of [C₁₆imC_n]­Br on the Brij 30/[C₁₆imC_n]­Br (n = 1, 2, 4, and 6) wormlike micelles were studied. When Brij 30 was mixed with the rodlike micelles of [C₁₆imC₈]­Br, the Brij 30/[C₁₆imC₈]­Br mixtures form wormlike micelles at low Brij 30 concentration and gels at high Brij 30 concentration. The [C₁₆imC_n]Br (n = 10, 12, 14, and 16) rodlike micelles were induced by Brij 30 to turn into the Brij 30/[C₁₆imC_n]Br gels. The effect of the [C₁₆imC_n]Br hydrocarbon chain length on their rodlike micelles with the addition of Brij 30 is also theoretically discussed.