Owing to their unique enrichment and phase-separation properties, coacervates not only enable the efficient capture and removal of pollutants but also differ fundamentally from conventional oil-water separation systems by operating in an aqueous environment, thereby offering significant advantages in pollutant remediation. Surfactant-based coacervates, in particular, exhibit superior solubilization capacity for pollutants while maintaining simple molecular structures and high degradability. Consequently, the development of surfactant-based coacervates holds considerable promise as an emerging technology for wastewater treatment. This study investigated the intermolecular interactions and aggregation behaviors of the mixed system comprising anionic cyclodextrin derivative sulfobutyl-β-cyclodextrin sodium salt (SBE-β-CD) and cationic gemini surfactant alkanediyl-α,ω-bis(dimethyldodecylammonium) bromide (12-s-12) through turbidity titration, cryo-transmission electron microscopy (Cryo-TEM), proton nuclear magnetic resonance (¹H NMR), and zeta potential analysis. The results reveal that upon gradually adding 12-s-12 to a fixed concentration of SBE-β-CD, the two components form complexes through electrostatic attraction and host-guest interactions, which further assemble into small-sized spherical aggregates. As the concentration of 12-s-12 increases, these spherical aggregates associate into larger chain-like aggregates via hydrophobic bridging between the tails of the complexes. With the gradual reduction of net charge in the system, the chain-like aggregates become increasingly entangled, ultimately leading to the formation of coacervates. When 12-s-12 is excessive in the system, the electrostatic repulsion between aggregates increase, causing the coacervates to revert to chain-like aggregates and eventually to small spherical aggregates. Comparison of coacervate formation regions for different 12-s-12 structures shows that as the methylene units in the spacer group of the gemini surfactants increase from 3 to 6, their ability to form coacervates with SBE-β-CD strengthens, resulting in a broader formation range. Besides, the coacervates formed by SBE-β-CD/12-6-12 can achieve complete enrichment and extraction of congo red and methyl orange from aqueous solutions, demonstrating excellent dye enrichment performance. In contrast, the system exhibits relatively low extraction efficiency for acid blue and methylene blue. This selective enrichment behavior suggests its application in the separation of dyes and wastewater treatment.

Key words: coacervate, dye enrichment, anionic cyclodextrin derivative, cationic gemini surfactant, aggregation behavior