Equilibrium Fusion–Fragmentation Dynamics Governs Nonequilibrium Sphere-to-Rod Transitions in Block Copolymer Micelles

The functionality of block copolymer micelles in applications spanning from drug delivery to nanomaterial synthesis is governed by their characteristically slow structural dynamics. Although techniques such as time-resolved fluorescence have enabled quantitative access to fusion and fragmentation dynamics at thermodynamic equilibrium, their specific role in directing stimulus-driven morphological transitions remains a pivotal unresolved question. By integrating time-resolved fluorescence quenching and temperature-jump dynamic light scattering on model Pluronic systems, we directly confront equilibrium fusion/fission rates with the kinetics of temperature-induced sphere-to-rod transitions. We demonstrate that the characteristic time scale of the nonequilibrium structural transition is directly governed by the elementary fusion rate constant measured at equilibrium. This quantitative correlation reveals that the macroscopic morphological transformation proceeds via stochastic, equilibrium-like fusion events, even under nonequilibrium morphological conditions. Our findings provide a critical bridge between equilibrium dynamics and nonequilibrium assembly, establishing that the kinetic pathway of a complex structural transition is encoded in the intrinsic single-event dynamics of the micelles.