Hydrogels Under Superchaotropic Control: Polyoxometalate Stabilization and pH-Responsive Crosslinking in Cellulose
Vighnesh B Lokare1, Amina Ledinic1, Nina Wehr2
1Institute of Physical Chemistry, RWTH Aachen University, Landoltweg, Aachen, Germany.
Angewandte Chemie (International Ed. in English)
|April 16, 2026
Summary
We stabilized polyoxometalates (POMs) in water using hydroxypropylcellulose (HPC), enabling pH-responsive hydrogels. This superchaotropic binding protects POMs and controls material properties.
Area of Science:
- Materials Science
- Supramolecular Chemistry
- Polymer Chemistry
Background:
- Polymer-polyoxometalate (POM) hybrid materials offer unique functionalities.
- The pH-dependent stability of POMs restricts their application in aqueous environments.
Purpose of the Study:
- To stabilize superchaotropic POMs in water using hydroxypropylcellulose (HPC).
- To develop pH-responsive HPC solutions and hydrogels through POM interaction.
Main Methods:
- Raman and NMR spectroscopy to analyze POM-HPC interactions and stability.
- Cloud point measurements, small-angle neutron scattering, and rotational rheology to study solution behavior and hydrogel properties.
Main Results:
- Hydroxypropylcellulose selectively stabilizes superchaotropic α-Keggin POMs ([PW12O40]3− and [SiW12O40]4−) against hydrolysis, extending their stability to near-neutral pH.
- POMs with higher charge and hydration that do not bind to HPC are not stabilized.
- pH-induced conversion of POMs triggers a transition in HPC from a bound, crosslinked state to an unbound, non-crosslinked state, enabling pH-switchable viscosity and gel-sol transitions.
Conclusions:
- Superchaotropic binding to HPC provides a general strategy for stabilizing POMs in water.
- This interaction enables the creation of pH-responsive soft materials with tunable properties.
- Superchaotropicity is a key phenomenon for designing advanced aqueous soft materials.
