Synthesis And Characterization Of Supramolecular Elastomers Based On Ionic Hydrogen Bond And Application In Flexible/Stretchable Strain Sensor

Ionic hydrogen bond,a form of ionic bonds,is a synergistic effect of ionic interactions and hydrogen bonds between anions and cations.Ionic hydrogen bond supramolecular elastomers（IHSEs）obtained by integrating ionic hydrogen bonds into polymer networks possess a favourable self-healing ability and sensitive response to p H or heat.These elastomers have been increasingly investigated recently,yet most of IHSEs are based on carbon backbones with amino and carboxyl functional groups,rarely PDMS main chains and those based on unsaturated carboxyl groups have not been reported.Therefore,from the point of view of enriching functional polymers,IHSEs are worthy of further development.Herein we describe an ionic hydrogen-bonded supramolecular polydimethylsiloxanes（PDMS）elastomer containing amino and unsaturated carboxyl groups produced via a facile and completely solvent-free synthesis route.Unsaturated carboxyl-grafted PDMS（UCS）and saturated carboxyl-grafted PDMS（SCS）were synthesized by reacting amino-grafted PDMS（APS）with maleic anhydride and succinic anhydride by simple mixing,respectively.The fact that IHSEs could be obtained by mixing UCS and APS while the mixture of SCS and APS was viscous fluid reveals difference of strength of ionic hydrogen bonds formed by unsaturated/saturated carboxyl groups with amino groups.To the best of our knowledge,it is the first time to investigate the role of unsaturated carboxyl groups which are conjugated with C=C on the strength of the ionic interactions.Stronger ionic hydrogen bonds from unsaturated carboxyl-amino complex were further confirmed by NMR titration.The mechanical properties and self-healing ability may be fine-tuned by adjusting the ion cross-linking density and-COOH and-NH₂ feed ratios.Furthermore,excess unsaturated carboxyl groups interact with substrates to form hydrogen bonds,making IHSEs practically adhesive.The optimized IHSEs with n（COOH）:n（NH₂）>1 were combined with carbon nanotubes and IHSEs@CNTs flexible/stretchable strain sensors were obtained.IHSEs were proved to be a good substrate for the preparation of flexible/stretchable strain sensors for wearable devices with comfort in the light of the evaluation of stretchability,Young’s modulus compared to skin and skin-bonding ability.IHSEs layer and CNTs layer were firmly bonded together duo to hydrogen bonds between the carboxyl groups on the IHSEs and CNTs.Besides,in the electrical performance tests our sensors were proved to be of low hysteresis,high sensitivity,high stability and good self-healing property,demonstrating a broad application prospect in durable wearable devices or electronic skin.Moreover,our IHSEs@CNTs flexible/stretchable strain sensors could be used to detect human motion and monitor patient symptoms such as cough,which shows that we aim to create better flexible/stretchable electronic sensors for wearable electronic devices and bring more convenience to people.