Mechanically Programmable Ionogels through a Dynamic Salting-Out Strategy.

Abstract

Gels exhibiting mechanically programmable strength under ambient conditions are essential for advancing flexible electronic devices. Here, a mechanically programmable ionogel based on choline chloride and poly(acrylic acid) (ChCl-PAA) is presented, with CaCl₂ being a key structural modulator. Using a dynamically controlled salting-out strategy, a crystal-domain-locking architecture is formed that enhances mechanical strength. The cooling rate governs the resulting microstructure and mechanical properties, rapid cooling at -20°C min ^-1 generates numerous defective CaCl₂ lattices, that effectively induce interpenetration of PAA chains via coordination and establish localized "crystal locks", producing a rigid network (Young's modulus 448 ± 14.21 MPa). Conversely, a slow cooling at -2°C min^-1 promotes the growth of large-sized densely packed CaCl₂ crystals, reduces polymer-crystal coupling, and yields to phase-separated morphologies. Accordingly, the slowly cooled ionogel exhibits a remarkably high elongation at break (687 ± 18%) and a markedly reduced Young's modulus (11.6 ± 1.15 MPa). Overall, this dynamically controlled salting-out strategy enables reversible hierarchical modulus regulation range spanning four orders of magnitude. This capability supports applications in reprogrammable adaptive devices, humidity-driven energy harvesters, rapid-response fire alarms, and bistable sensors that switch between rigid and ductile states. These findings provide a versatile design strategy for adaptive polymer-inorganic hybrid systems with mechanically programmable strength, electrical conductivity, and multifunctional stimulus responsiveness.