Preparation And Properties Of Mechanically Strong Ionic Conductive Elastomers

Electronic skin is a new type of material inspired by biological skin tissue,which has been widely studied in recent years.Electronic skin is widely used in sports recording,health monitoring,environmental perception and other fields.With the development of its application scenarios,electronic skin puts forward higher requirements for strength,elasticity,sensitivity and other properties,and also brings many challenges.Ionic conductive elastomer is a new type of conductive material that can meet these requirements.As far as most of the currently developed ionic conductive materials used in electronic skin are concerned,elasticity and electrical conductivity of the material are more considered,and little consideration is given to the mechanical strength of the ionic conductive materials.This brings these ionic conductive materials with a large number of problems such as not durable,fragile,etc.Therefore,preparing an ionic conductive elastomer with excellent mechanical properties,high elasticity,high sensitivity,and solvent-free is a promising and challenging task.This paper’s main research content is divided into the following two parts:（1）Based on the cross-linked structure and dual-ion-conducting system,a series of novel cross-linked dual-ion-conducting elastomers（CDICEs）with high strength,high elasticity,and high sensitivity were synthesized.In the case of proper monomer ratio and ionic salt addition,this ionic conductive elastomer exhibits many excellent properties.Among them,the cross-linked structure formed by the copolymerization of long-chain polydimethyldiacrylate（PEGDM）and acrylic acid（AA）,and the hydrogen bonding between polyacrylic acid segments improve the mechanical strength of the elastomer.The added Lithium bis（trifluoromethanesulfonyl）imide（Li TFSI）and choline chloride（Ch Cl）can respectively complexe with the PEG chain segment and form a deep eutectic system with the carboxyl group in the PAA chain segment,thereby jointly improving the conductivity of the crosslinked elastomer.The optimal tensile strength of this type of CDICE can reach 16.4 MPa,and the optimal breaking strain can reach 1410%.CDICEs also have good electrical conductivity(0.5×10^-3-8.3×10^-3 S·m^-1,25°C),wide operating temperature range（-44.5°C-150°C）,and extremely high transparency（>95%）.Wearable sensors made of this elastomer can sensitively monitor body movements such as finger bending,nodding,and wrist flipping.As a durable and reliable material,it has broad application prospects in fields such as electronic skin and wearable devices.（2）Designed and synthesized a high-strength,healable polyurethane ion-conducting elastomer based on multi-level hydrogen bonding.The classic Li/PEO conductive system formed by the polyethylene glycol segment in polyurethane and Li TFSI provides ionic conductivity for this type of elastomer.The multi-level hydrogen bonding in polyurethane can endow the elastomer with high strength,high elongation and repairability.Generally,the self-healing ability of ion-conducting elastomers relies on reversible bonds such as metal ion complexation,disulfide bonds,and low-density hydrogen bonds.This type of action can provide elastomers with excellent self-healing properties,but at the same time generally lacks high mechanical properties.The strength of the current self-healing ion-conducting elastomers is mostly at the level of about 1 MPa,and they will face a lot of problems in the application process.In this system,multi-level strong and weak hydrogen bonds can be formed between functional groups such as urea group,amidourea（ASCZ）,and carbamate on the polyurethane main chain.The multiple strong hydrogen bonds between ASCZ can greatly improve the mechanical strength of the elastomer.At the same time,the synergistic effect of high-density single weak hydrogen bonds and multiple strong hydrogen bonds can make the elastomer have better repair ability.PUICE-3/8 elastomer exhibits excellent tensile strength（～5.7 MPa）,good elongation at break（～850%）and good electrical conductivity(～1.5×10^-4 S m^-1).Moreover,after repairing at 80°C for 18 h,it can achieve a self-healing efficiency of more than 90%in terms of mechanical properties.Due to its high strength,high toughness,and excellent properties of healing,the prepared PUICE has important application value in the fields of flexible sensors and motion monitoring.