Synthesis and investigation of chemomechanical gels driven by the Belousov–Zhabotinsky reaction: insights into ligand influence

Abstract Self-oscillating chemomechanical gels powered by the Belousov–Zhabotinsky (BZ) reaction represent a promising class of smart materials for soft robotics and autonomous systems; however, a comprehensive understanding of how the catalyst’s chemical structure governs their performance is still lacking. This work investigates the relationship between ligand hydrophobicity in immobilized iron-based BZ catalysts and the resultant chemomechanical response of poly( N -isopropylacrylamide) hydrogels. A series of heteroleptic iron complexes with systematically varied ligand hydrophobicity – bis(1,10-phenanthroline)(5-acrylamido-1,10-phenanthroline) iron(II) sulfate, bis(4,4′-dimethyl-2,2′-bipyridine)(5-acrylamido-1,10-phenanthroline) iron(II) sulfate, and bis(2,2′-bipyridine)(5-acrylamido-1,10-phenanthroline) iron(II) sulfate, as well as bis(bathophenanthroline)(1,10-phenanthroline) iron(II) sulfate – were synthesized and incorporated into the polymer network. The gels’ self-oscillating behavior, morphological structure (via SEM), and elastic properties were characterized. It was found that increasing ligand hydrophobicity significantly enhances the amplitude of chemomechanical oscillations while concurrently reducing the elastic modulus of the gel. These results demonstrate that ligand hydrophobicity is a critical design parameter for tuning the performance of self-oscillating gels, paving the way for optimizing next-generation autonomous soft actuators and pumps.