Flexible ionic-gel strain sensor with double network, high conductivity and high frost-resistance using electrohydrodynamic printing method

Ionic-gel sensors have attracted wide attention in the fields of flexible electronic skin and wearable devices. However, the weak mechanical properties of ionic gels have hindered their large-scale applications. In this work, the electrohydrodynamic (EHD) printing method was proposed to prepare the ionic-gel film in the PDMS mold, and then the ionic-gel film with the double-network (DN) structure was formed under the induction of ultraviolet (UV) light, which greatly improved the electrical conductivity of the ionic-gel film. The CS-(AA-HEMA)-DN ionic-gel film was prepared via interpenetrating the acrylic acid and 2-hydroxyethyl methacrylate (AA-HEMA) network into chitosan (CS) network in 1-butyl-3-methylimidazolium chloride ([BMIM]Cl). The tensile strength of the CS-(AA-HEMA)-DN ionic-gel film is 0.28 MPa under 335 % strain. The electrical conductivity is 1.231 × 10-3 S/cm, and the response time is 81 ms. Therefore, the CS-(AA-HEMA)-DN ionic-gel film has excellent mechanical properties, high conductivity, and fast response time at room temperature. In addition, the CS-(AA-HEMA)-DN ionic-gel film has high frost-resistance and still has good mechanical properties, high conductivity and stability at a low temperature (−60 ℃). The CS-(AA-HEMA)-DN ionic-gel film can be used as a flexible strain sensor for monitoring human motion due to its superior electromechanical properties. Thus, the high-performance flexible ionic-gel strain sensor has broad application prospects in the field of flexible electronics.