Valence-Controlled Flexibility and Gelation in Cerium–Polyoxometalate Subnanowires

Subnanometer inorganic nanowires (SNWs) exhibit polymer-like flexibility, yet the ability to rationally control their rigidity remains a fundamental challenge. Here we demonstrate that the flexibility of phosphomolybdic acid–cerium oxide hybrid SNWs can be precisely modulated by redox-governed cerium valence transitions. Using time-resolved SAXS, we show that the persistence length of SNWs can be tuned from ∼2452 Å (rigid, Ce4+) to ∼20 Å (flexible, Ce3+) upon thermal treatment, as verified by XPS. The resulting SNWs form hierarchical gels whose viscoelastic properties scale with nanowire flexibility, with storage moduli ranging from ∼104 Pa for semiflexible gels to ∼102 Pa for rigid ones. Semiflexible SNWs yield an optimized network that balances entanglement and free volume, leading to relaxation dynamics distinct from classical polymers and colloidal glasses. This work establishes a direct link between inorganic redox chemistry, nanoscale chain flexibility, and macroscopic gel performance, offering a strategy for designing mechanically tunable subnanometer soft materials.