Light-Driven Topological Relaxation and Dynamic Scaling in Photoresponsive Polymer Films

Across nature, when systems are driven far from equilibrium, topological defects emerge as universal signatures of how order emerges from disorder. Their formation reflects the interplay between the competing time scales of driving and relaxation that govern their self-organization. Here, we investigate this process in light-responsive azopolymer films that spontaneously self-organize under continuous illumination through photoisomerization and phase separation. By tracking the spatiotemporal evolution of the emerging surface morphology, we identify a characteristic freeze-out timethe intrinsic time scale over which the initially uniform film transitions to an ordered pattern. Correlating this time scale with the defect density reveals a robust positive power-law scaling, where slower ordering near the illumination threshold yields higher defect densities, while stronger excitation accelerates domain formation and produces more coherent, defect-sparse patterns. This behavior is consistent with a self-limited regime in which pattern formation is governed primarily by the material's intrinsic photomechanical relaxation rather than by externally imposed rates. Following the initial pattern formation, we observe a secondary self-annealing regime mediated by transient vortex-antivortex pairing that drives further defect annihilation and surface refinement. These results establish light-driven azopolymers as a versatile and fully optical platform for probing universal kinetic laws of defect evolution, dynamic topological ordering, and nonequilibrium relaxation in soft photonic materials.