Synthesis, surface/interfacial properties, and biological activity of amide-based Gemini cationic surfactants with hydroxyl in the spacer group

Three amide-based Gemini cationic surfactants, 1, 3-2 (alkyl amide propyl dimethyl ammonium chloride) iso-propyl alcohol (abbreviated to ADQ-n, where n represents the carbon number in the raw fatty acid of 8, 12 and 16) were synthesized by a facile synthetic route. The effect of hydrophobic chain length on surface/interfacial activities, electrolytes tolerance, wettability, foaming properties were investigated. The effect of electrolytes (NaCl and CaCl2) on the interfacial tension at the oil/water interface were discussed, and the biological activity was also tested. The results showed that ADQ-n have the higher surface activities than conventional monomeric surfactant. The critical micelle concentration (cmc) decreases with the increase of hydrophobic chain length, however, the surface tension at the cmc (gamma(cmc)) shows the opposite trend. There are few differences for maximum surface excess concentration (Gamma(max)) and minimum area per molecule (Amin). ADQ-12 has the lowest interfacial tension value (4.1 x 10(-3) mN/m) than other synthesized Gemini surfactants, this is attributed to the better compatibility between hydrophobic tail of ADQ-12 and kerosene. In addition, the addition of electrolytes is favorable to decrease interfacial tension at oil/water interface. ADQ-n demonstrated readily biodegradation (> 97%) in comparison with conventional alkyl chain Gemini surfactants (< 37%) after seven days and could be classified as biodegradable.