Regulation of the rheological behavior of dilute surfactant solutions by hydrophobically associating polymers

To construct polymer–surfactant mixed systems, hydrophobically associating polymers(GY-1 and GY-2) were combined with an amphoteric surfactant (BEF-O) and an anionic surfactant (SDS), respectively. Rheological measurements, cryo- scanning electron microscopy (cryo-SEM), and steady-state fluorescence spectroscopy were employed to systematically investigate the macroscopic rheological properties, microstructural characteristics, and the synergistic interaction mechanisms between polymers and surfactants. Rheological results revealed that the combinations of GY-1 or GY-2 with BEF-O or SDS exhibited synergistic viscosity-enhancing effects to varying extents. Specifically, the synergistic viscosity enhancement of the 0.4wt% BEF-O/0.2wt% GY-2 system (69.6 mPa·s) was approximately 1.9 times that of the 0.4wt% BEF-O/0.2wt% GY-1 system (35.7 mPa·s). In contrast, the synergistic viscosity enhancement of the 0.02wt% SDS/0.2wt% GY-1 system (66.7 mPa·s) was approximately 8.8 times higher than that of the 0.02wt% SDS/0.2wt% GY-2 system (7.6 mPa·s). These results indicate a clear matching relationship between surfactant micellar structure and polymer molecular weight: long-chain surfactants (BEF-O) preferentially interact with high-molecular-weight hydrophobically associating polymers (GY-2), whereas short-chain surfactants (SDS) are more likely to interact with low-molecular-weight polymers (GY-1). Steady-state fluorescence and cryo-SEM results indicate that pronounced hydrophobic association exists in both the BEF-O/GY-2 and SDS/GY-1 systems: in the BEF-O/GY-2 system, the hydrophobic side chains of GY-2 insert into BEF-O wormlike micelles, and multipoint associations promote the formation of a stable three-dimensional network; in contrast, in the SDS/GY-1 system, GY-1 more readily associates with SDS spherical micelles, enabling the formation of a stable three-dimensional network even at relatively low concentrations. These findings provide a theoretical basis for the rational design of efficient polymer–surfactant synergistic thickening systems.