The counterion-mediated controllable coacervation of nano-ions with polyelectrolytes

Nano-ions can complex with polyelectrolytes for coacervates with hierarchical structures; however, the rational design of functional coacervations is still rare due to the poor understanding of their structure- property relationship from their complex interaction. Herein, 1 nm anionic metal oxide clusters, PW12O40 3-, with well-defined, mono-disperse structures are applied to complex with cationic polyelectrolyte and the system shows tunable coacervation via the alternation of counterions (H' and Na') of PW12O40 3-. Suggested from Fourier transform infrared spectroscopy (FT-IR) and isothermal titration studies, the interaction between PW12O40 3-and cationic polyelectrolytes can be modulated by the bridging effect of counterions via hydrogen bonding or ion-dipole interaction to carbonyl groups of polyelectrolytes. The condensed structures of the complexed coacervates are explored by small angle X-ray and neutron scattering tech-niques, respectively. The coacervate with H' as counterions shows both crystallized and discrete PW12O40 3 -clusters, with a loose polymer-cluster network in comparison to the system of Na' which shows a dense packing structure with aggregated nano-ions filling the meshes of polyelectrolyte networks. The bridging effect of counterions helps understand the super-chaotropic effect observed in nano-ion system and pro-vides avenues for the design of metal oxide cluster-based functional coacervates.(c) 2023 Elsevier Inc. All rights reserved.