Valence-Controlled Flexibility and Gelation in Cerium-Polyoxometalate Subnanowires

Area of Science:

• Materials Science
• Nanotechnology
• Chemistry

Background:

• Subnanometer inorganic nanowires (SNWs) possess polymer-like flexibility, but controlling their rigidity is challenging.
• Developing methods to tune the mechanical properties of SNWs is crucial for advanced material design.

Purpose of the Study:

• To demonstrate precise modulation of SNW flexibility through redox-governed valence transitions.
• To establish a link between inorganic redox chemistry, nanoscale flexibility, and macroscopic material performance.

Main Methods:

• Utilized phosphomolybdic acid-cerium oxide hybrid SNWs.
• Employed time-resolved small-angle X-ray scattering (SAXS) to measure persistence length.
• Verified cerium valence states using X-ray photoelectron spectroscopy (XPS).

Main Results:

• Achieved tunable persistence length of SNWs from ~2452 Å (rigid, Ce⁴⁺) to ~20 Å (flexible, Ce³⁺) via thermal treatment.
• Demonstrated that viscoelastic properties of hierarchical gels formed by SNWs scale with nanowire flexibility.
• Observed unique relaxation dynamics in semiflexible SNW gels, distinct from polymers and colloidal glasses.

Conclusions:

• Redox chemistry in cerium oxide enables precise control over inorganic nanowire flexibility.
• Mechanically tunable subnanometer soft materials can be designed by linking redox chemistry to nanoscale chain flexibility.
• This approach offers a new strategy for creating advanced soft materials with tunable mechanical properties.