Temperature‐Dependent Self‐Aggregation and Microstructure of Reverse Poloxamer <scp>10R5</scp> in the Surface‐Active Ionic Liquid [ <scp>BMIM</scp> ][ <scp>OSU</scp> ] Probed by <scp> ² H NMR </scp> and <scp>SANS</scp>

ABSTRACT The self‐assembly of amphiphilic block copolymers in aqueous media is central to their applications in drug delivery and nanostructured materials. Poloxamer 10R5, a reverse nonionic triblock copolymer composed of poly(propylene oxide)–poly(ethylene oxide)–poly(propylene oxide) (PPO–PEO–PPO), exhibits temperature‐dependent micellization in water. In this work, we investigate the influence of the surface‐active ionic liquid (SAIL), 1‐butyl‐3‐methylimidazolium octyl sulfate ([BMIM][OSU]), on the temperature‐ and concentration‐dependent aggregation behavior of Poloxamer 10R5 using nuclear magnetic resonance (NMR) spectroscopy and small‐angle neutron scattering (SANS). NMR spin‐relaxation reveals restricted mobility of [BMIM][OSU] with increasing concentration from 20 to 200 mM in the presence of 10R5 (200 mM). SANS results show temperature‐induced transitions from unimers to prolate ellipsoidal micelles and demonstrate that [BMIM][OSU] induces aggregation below the critical micelle concentration and modifies micelle morphology at higher concentrations. These findings highlight the hydrophobic interactions between the SAIL and hydrophobic PPO blocks and provide insight into tuning block‐copolymer self‐assembly through SAIL additives. Overall, this study provides a detailed understanding of the influence of SAILs on the temperature‐ and concentration‐dependent aggregation behavior of block copolymers, offering potential for tuning poloxamer 10R5‐SAIL systems for applications in materials science and nanotechnology.