Reordering-mediated nucleation dynamics in early stage phase separation.

Classical nucleation theories relying on quasi-equilibrium thermodynamics fail to capture the far-from-equilibrium structural reordering inherent to early stage condensed-cluster formation. We develop a framework that maps a continuous structural field onto a core-shell model, coupling local non-conservative reordering with mesoscopic phase-boundary propagation. By evaluating the reordering-mediated nucleation time, we analytically distinguish the static potential energy profile from the effective nucleation barrier. Our mean-field solution reveals a kinetic turnover effect: beyond a critical structural-density coupling threshold, rapid reordering dynamics induce a steep interfacial gradient in the structural field, incurring an energetic penalty that suppresses the net driving force for nucleation. This behavior highlights a fundamental non-reciprocity between cluster growth and local structural relaxation. The reordered intermediate states replicate experimentally observed size-dependent structural gradients and offer a resolution to discrepancies between classical predictions and measured nucleation rates, providing testable criteria for multi-step pathways in nanocrystallization and biomolecular condensation.