Cellulose-mediated ionic liquid crystallization enables tough-stiff switchable ionogels.

Nature has inspired to fabricate mechanically switchable materials for applications in various aspects, which is, however, unique but challenging to achieve reversible phase transitions using common ionic liquids in ionogels with ambient temperature-triggered crystallization feature. Here, we develop a tough-stiff switchable ionogel through a reversible solvent crystallization design. Cellulose acts as a chemical regulator, competitively binding with polymers to promote the formation of ionic liquid crystals. This results in a tough ionogel with a bulk toughness of 25.7 MJ m-3 and a fracture toughness of 47.1 kJ m-2, which can switch into a stiff ionogel with a tensile modulus of 134.6 MPa and a compressive modulus of 48.9 MPa. Upon heating, the crystallized ionogel reverts to its unconfined as ionic liquid crystals melt. This phase-driven structural and rigidity transition enables dynamical programming, with rapid, reversible and repeatable shape recovery through heating. Our study demonstrates solvent crystallization in ionogels, offering a strategy for creating intelligent, reconfigurable, and performance-switchable materials with customizable functions.