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.