Smart Superchaotropicity – Superchaotropic Polyoxometalate Binding as an Addressable Switch in Aqueous Polymer Systems

• Applicant: Dr. Max Hohenschutz
• Subject Area: Physical Chemistry of Molecules, Liquids and Interfaces, Biophysical Chemistry ; Synthesis and Properties of Functional Materials
• Term: since 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 534870847

In this project we will investigate the switchability of non-ionic bio-polymers/polyoxometalate complexes in water. These complexes are based on a so-called superchaotropic binding process. The underlying (super)chaotropic effect is due to the low charge density of the polyoxometalates, which leads to their weak hydration, and causes them to bind strongly to non-ionic polymers. Since the charge density of the polyoxometalates can be adjusted by irradiation with UV light, change of pH or electric fields, the polymer/polyoxometalate binding reaction can be controlled. Thus, when the charge density of the polyoxometalate is reduced - as induced by UV light, for example - and hydration is increased, the binding to the polymer chain is weakened. This switching by "Smart Superchaotropicity" is reflected as a sharp decrease in viscosity or gelation of cellulose-based bio-polymers in the presence of the polyoxometalates. This concept will offer a novel strategy for generating switchable viscous solutions and gels based on non-ionic polymers, which can otherwise acquire switchable properties only through directed synthesis. In addition to the stimulation (pH, light, electric fields) of the rheological properties of these systems, we aim to trace the concomitant effects in solution structure and gain fundamental insights into the superchaotropic binding process. To this end, we will measure diffusion coefficients, binding constants and stability of polyoxometalates before and after stimulation. This methodology will allow us to draw conclusions about the time scale of superchaotropic binding and the binding strength, and evaluate the effect of binding to the polymer on solution chemistry of the polyoxometalates.

• DFG Programme: Research Grants