Kinetic gating of interfacial instability directs topology evolution in flow-regulated interfacial polymerization.

Interfacial polymerization (IP) is fundamentally governed by the reaction-induced phase separation (RIPS), a condensed chemical process that enables the fabrication of functional polymer films, microcapsules, and nanofibers. However, IP topology evolution is highly non-equilibrium, with thermodynamic phase separation and kinetic barriers remaining difficult to decouple and control. In this work, we isolated and quantified thermodynamic-kinetic competition using coaxial microfluidics, employing fluid advection as a tunable kinetic parameter to gate thermodynamic instability. Two distinct pathways emerge: thermodynamically-dominated yielding disordered precipitation, and kinetically-dominated suppressing bulk separation and enabling ordered growth. Additionally, we proposed steady interfacial flow velocity as a quantitative descriptor, validated by phenomenological modeling and experimental data. Furthermore, a reaction-diffusion-advection model was developed to reveal the microscale free energy landscape governing oligomer generation versus advective removal. This framework demonstrates how external kinetic fields regulate non-equilibrium topological pathways, enabling predictive rational design of functional polymers through condensed chemical principles.