Professor Hu Jian of Xi'an Jiaotong University (XJTU) has made a breakthrough regarding ionic liquid gel with high mechanical properties in cooperation with Professor Michael Dickey of North Carolina State University.

They proposed a simple general design principle based on in situ phase separation. Through one-step rapid random copolymerization, two polymer components with very different solubility properties can form a bicontinuous phase separation structure in situ in ionic liquids, which can allow the strength of ionic liquid gel to reach 12.6 MPa, the toughness to reach 24 kJ/m2, the modulus to reach 46.5 MPa, and the stretchability to reach 600%.

 It can also achieve multifunctionality that includes self-recovery, self-healing, shape memory, anti-swelling, and 3D printability, which reveals the working mechanism of high mechanical performance and versatility from the perspective of phase-separated structures.

This study shows that the high strength and high modulus of ionic liquid gels originate from the continuous hard phase. The high toughness originates from hydrogen bond energy dissipation in the hard phase and the interpenetrating phase-separated structure of the hard and soft phases.

The high stretchability originates from the large deformation of the continuous soft phase, while the multifunctionality, such as self-recovery, self-healing, and shape memory, originates from hydrogen bond-breaking and rearrangement in the gel hard phase.

The in situ phase separation technology is suitable for various common monomers and ionic liquids, and does not require the tedious post-processing operations necessary for traditional phase separation technology. This can help researchers easily prepare high mechanical properties of ionic liquid gels and expand their application space.

The research results were published in Nature Materials with the title Tough and stretchable ionogels by in situ phase separation. The first author of the paper is Wang Meixiang, who graduated from XJTU with a doctoral degree. Hu and Dickey are the co-corresponding authors. (Link to the paper: https://www.nature.com/articles/s41563-022-01195-4)

The first unit of the paper is the State Key Laboratory for Strength and Vibration of Mechanical Structures. The research was financed by the National Natural Science Foundation of China.