P(NiPAAm-co-AA) organogel beads were prepared by UV induced droplet polymerisation and then mechanically reinforced through treatment with iron(III) chloride. Energy dispersive X-ray spectroscopy mapping revealed that the resulting structure depends on the amount of iron incorporated. Beads with a low iron(III) loading show a core and shell architecture, while high loadings result in a more homogeneous distribution of the ions over the particle volume. Fourier transform infrared analysis and proton release indicate that the iron(III) ions coordinate to the carboxylic entities formed in the copolymer.
A colorimetric thiocyanate assay allowed the authors to quantify the iron uptake and to identify a limit at a ratio of iron to carboxylic groups of approximately 1 to 3.8. The compressive Young modulus of the 5 millimetre beads increased by a factor of 378, from 6.1 kilopascal in the parent gel to 2.3 megapascal in the iron saturated beads. Despite this large gain in stiffness, the gels retain a highly reversible shrinkage and swelling during solvent exchange between ethanol and ethyl acetate.
Reinforced beads with a low and a high iron content, conditioned in ethanol, shrink by 38 percent and 25 percent of their volume respectively after immersion in ethyl acetate. The time constants for shrinkage increase most significantly with the iron content, while the rate of swelling remains comparable. No iron(III) leaching was detected over multiple swelling and shrinking cycles, which indicates that the reinforcement is stable in repeated use and brings robust, chemically responsive materials for smart valves and adaptive flow control a step closer.
The study was carried out at the Institute of Technical and Macromolecular Chemistry at the University of Hamburg within project A01 of the Collaborative Research Centre CRC 1615 (SMART Reactors).
Johannes Gmeiner, Jonah Hasse, Gerrit A. Luinstra (2026). Iron(III) ion reinforced P(NiPAAm-co-AA) beads as tunable smart organogels. Polymer International, Early View.
