Solvent‐Mediated Self‐Assembly of Nonionic Surfactant Polyoxyethylene (10) Oleyl Ether in Water–Ethylene Glycol Mixtures

Surfactants self‐assemble into diverse nanostructures in solvents ranging from water to organic solvents, ionic liquids and even deep eutectic solvents. Among these, mixtures composed of water and polyols exhibit tunable physicochemical properties, making them ideal for controlling aggregation. Here, we systematically investigated the self‐assembly of the nonionic surfactant polyoxyethylene (10) oleyl ether (C 18‐1 EO 10 ) in the water–ethylene glycol (EG) binary mixtures. Surface tension measurements reveal that the critical micelle concentration increases monotonically with EG content, reflecting the attenuated solvophobic interactions. The phase behavior was investigated using small angle X‐ray scattering, polarized optical microscopy and rheology. The phase diversity of lyotropic liquid crystals (LLCs) progressively decreases with EG content. Structural analysis of LLCs suggests that C 18‐1 EO 10 adopts a looser packing with the addition of EG. Rheological results demonstrate that EG addition reduces mechanical strength and thermal stability, consistent with the cohesive energy of solvents. Our findings develop a simple method to adjust the self‐assembly of surfactants by tuning binary mixture composition, expanding the applications of ordered molecular aggregates in various media.