Additive-Driven Micellar Growth and Morphological Transitions in Tetronic Block Copolymers: Insights from Experimental and Computational Study

The self-assembly of Tetronics® block copolymers is strongly influenced by additives that modify hydration and interfacial packing within micellar structures. Here, we investigate how octanoic acid (OA) and perfluorooctanoic acid (PFOA) alter the solution behavior of Tetronics® T1304 and T1307 using a combination of cloud point (CP), relative viscosity (η_rel) small-angle neutron scattering (SANS), dynamic light scattering (DLS), transmission electron microscopy (TEM), pyrene fluorescence, and density functional theory (DFT) calculations. In the presence of OA, T1304 exhibits pronounced micellar growth, progressing from spherical to ellipsoidal aggregates and, at higher concentrations, to vesicular structures. These changes arise from OA-induced dehydration of the PEO corona and enhanced packing of PPO domains, as confirmed by increases in aggregation number, low-Q scattering intensity, and a marked decrease in the pyrene I₁/I₃ ratio. In contrast, PFOA produces only modest changes in micellar size while preserving spherical topology over the same concentration range. Although DFT analysis indicates stronger electronic stabilization for Tetronics®-PFOA complexes than for OA, the rigid and lipophobic nature of the fluorocarbon chain limits its ability to penetrate the PPO core and drive curvature changes. The combined experimental and computational results show that additive-induced dehydration and steric compatibility, rather than electronic affinity alone, determine the structural evolution of Tetronics® micelles.