Sulfonic-Hydroxyl-Type Heterogemini Surfactants Synthesized from Unsaturated Fatty Acids

Novel anionic heterogemini surfactants have been synthesized from two kinds of unsaturated fatty acids (oleic acid and petroselinic acid). The hydrocarbon chain is covalently bound to the terminal carbonyl group of the unsaturated fatty acids and hydrophilic headgroups (i.e., sulfonic and hydroxyl groups) are introduced to the cis double bond. The aqueous solution properties of the surfactants synthesized here have been studied on the basis of static/dynamic surface tension, conductivity, fluorescence, and dynamic light scattering (DLS) data. We have mainly focused on the following two factors that may significantly impact the aqueous solution properties of the surfactants: one is hydrocarbon chain length and the other is molecular symmetry. The first key result from our current study is that increased hydrocarbon chain length results in a closely packed monolayer film at the air/aqueous solution interface, even at low concentrations as a result of the increased hydrophobicity of the longer chain analogue. We have previously observed a similar trend when aqueous solution properties of oleic acid-based phosphate-type heterogemini surfactants were studied. The second key finding of our current research is that increased molecular symmetry results in greater surface activities (which include lower aqueous surface tension and greater molecular packing at the air/aqueous solution interface). In addition, it seems likely that the size of molecular assemblies spontaneously formed in bulk solution decreases when the molecular symmetry increases. These results suggest that the symmetric analogue provides greater hydrophobic environments, although the exact reason for this is not yet known.