Self-healable And Shape Memory Gels Based On Reversible Non-covalent Bonds

In recent years,gel-based wearable sensors have attracted great attention in the field of human motion detection due to the advantages of good flexibility and high sensitivity.However,gels are usually hard to heal after fracture due to the poor mechanical properties when they are converted into electrical signals due to external deformation（such as stretching,compression,or bending）.The polymer network and supramolecular interaction can increase the toughness of the gels and promote its self-healing by means of reversible interaction with non-covalent bonds.Therefore,in this paper,poly（vinyl alcohol）/ionic liquid（PVA/IL）multi-functional gels with self-healing and shape memory effect based on reversible non-covalent bonds（hydrogen bonds,electrostatic interaction,and metal coordination）was prepared by molecular structure design.The relationship between the structure and properties of the gel was studied by scanning electron microscopy（SEM）,differential scanning calorimetry（DSC）,thermogravimetric analysis（TGA）,infrared analysis（FTIR）,swelling test and tensile compression test,and its biocompatibility was evaluated.The application of gel in strain sensor sound recognition and other aspects was explored through electrochemical performance test.The specific research contents include:1.Since the abundant hydroxyl groups in the side chains of PVA could form hydrogen bonds with the strongly electronegative atoms N,F in the anionic groups of 1-butyl-3-methylimidazolium tetrafluoroborate（BMIMBF₄）,the polymer solution transferred spontaneously to gel by one-step self-assembly at room temperature with the help of a large number of non-covalent hydrogen bonds and electrostatic interaction between PVA and IL.The reversibility of hydrogen bond and electrostatic interaction endows polyvinyl alcohol/ionic liquid gels（PVA/IL）excellent self-healing function,good strength,and toughness.Moreover,the content of ionic liquid has a significant effect on the properties of PVA/IL gels.The existence of reversible bonds and the fluidity of PVA macromolecular chains ensure the high self-healing efficiency of 92.60%.Moreover,the gel can form metal coordination bonds with Fe³⁺in ferric sulfate solution,and can be reduced in ascorbic acid（V_c）solution,leading to good redox-driven shape memory effect.The results show that the tensile strength and elongation at break of the gels with higher IL content are 1.447 MPa and 750%,respectively,and the compressive stress could reach up 150 KPa when it was compressed to 50%.The selected polymer matrix is PVA,which is a biocompatible non-toxic environment-friendly polymer,and IL is also a green solvent with excellent electrical conductivity.Therefore,the prepared gels have good electrical conductivity and excellent sensing performance,which can accurately monitor the bending movement of human joints and vocal cord vibration.2.Because the N,O,F atoms in PVA and IL molecules can form high binding strength and reversible metal chelation with bivalent and trivalent metal ions,it is conducive to the improvement of gel properties.In addition,the reversibility of metal chelation can also promote the self-healing of the gels.Therefore,in order to improve the mechanical properties and self-healing ability simultaneously,Fe³⁺was introduced to form coordination bonds in PVA/IL gel matrix to improve the gel properties.Compared with PVA/IL gels,the self-healing efficiency of PVA/IL/Fe gel was increased by about 1.4 times.Tensile strength,elongation at break and compressive stress under 50%compression was increased by 76.6%,17.2%and 44.0%,respectively.PVA/IL/Fe gel also showed solvent-driven shape memory effect.Furthermore,the sensitivity of the gels was enhanced due to the conductivity of the metal ions.In summary,PVA/IL gel based on reversible non-covalent bond not only has excellent mechanical properties of self-healing and shape memory function,but also has good biocompatibility,which can realize the sensing application of stress and strain sensing and speech recognition,and has a broad application prospect in tissue engineering sensors and response components.