Effect of a Hydrophilic Head Group on Krafft Temperature, Surface Activities and Rheological Behaviors of Erucyl Amidobetaines

Ultra-long-chain amidobetaine surfactants have become one of the hot topics recently, but the influence of the hydrophilic head group on the aggregation behaviors and the correlation between surface activities and thickening ability have been less documented. In this work, comparative studies on the effect of the hydrophilic group on Krafft temperature (T (K)), surface activities and rheological behaviors of erucyl amidobetaines with sulfonate, hydroxyl-sulfonate or carboxylate were examined. Compared to the sulfobetaines, the carboxybetaine is more water-soluble; the addition of an hydroxyl group onto the head group of sulfobetaine increases water-solubility leading to a lower T (K). Unexpectedly, the nature of the head groups has little effect on the critical micelle concentration and thickening ability of these surfactants. The packing parameter prediction verifies the formation of wormlike micelles which accounts for the strong thickening ability of the surfactant aqueous solutions.