Adsorption and Aggregation Properties of Multichain Anionic Amphiphilic Oligomers Consisting of Dodecyl Acrylamide and Sodium Acrylate

: Multichain amide-bonded anionic amphiphilic oligomers consisting of dodecyl acrylamide and sodium acrylate (i.e., xC₁₂AAm-yAA, where x and y represent the number of dodecyl acrylamide (C₁₂AAm) and sodium acrylate (AA) units, respectively) were synthesized via the radical oligomerization of two monomers in the presence of 2-aminoethanethiol hydrochloride. Equilibrium and dynamic surface tension, pyrene fluorescence, dynamic light scattering, and steady-state fluorescence quenching measurements were used to characterize the properties of the oligomers. In addition, the effects of the polymerization degree and number of dodecyl chains and hydrophilic groups on these properties were evaluated via comparison of these results with those of previously reported amphiphilic oligomers with ester bonds and conventional anionic monomeric surfactants. xC₁₂AAm-yAA exhibits lower critical micelle concentration (cmc) values than conventional sodium n-dodecanoate surfactant, indicating their excellent micelle-forming ability despite the large molecular structure with a long polymer main chain. The 3.0C₁₂AAm-7.5AA oligomer features the lowest cmc. The surface tensions of xC₁₂AAm-yAA at the cmc are lower than those of the conventional surfactant, which indicates that the oligomers adsorb and orient efficiently at the air-water interface. Further, xC₁₂AAm-yAA forms small aggregates with diameters of ~10 nm and aggregation numbers of 2-8 as well as large aggregates composed of masses of small aggregates. An increase in the polymerization degree of the oligomers decreases the aggregation number of the small aggregates; this indicates that it is more difficult for oligomers with long polymer chains to form aggregates due to their bulky structure.