Poly(Polymerizable Deep Eutectic Solvents)-based Transparent Conductive Elastomers For Flexible Electronic Devices

Flexible electronics have become ubiquitous in daily life since the rapid development of electronic technology and the widespread use of smart electronics.The properties of flexible conductive materials,including their mechanical and electrical properties,can be easily tuned by controlling the crosslinking density of the polymeric networks,and this feature has aroused the interest of researchers in the design of materials with multifunctionality and practicality.At present,most of the reported flexible conductive materials have problems,such as some flexible conductive materials are high costs or cumbersome preparation process,restricting their applications in the fields of flexible optoelectronics;the hydrogel is easily affected by the environment,and the water is easy to evaporate in high temperature or low humidity environment;there is potential threat to humans or the environment due to that ionic gels present a risk of liquid leakage;these increasing demands and short lifetimes of modern electronics have resulted in the growth of electronic waste and these abandoned electronic materials have led to increasingly serious environmental problems;and so on.Therefore,in order to solve the above problems,a variety of novel polymerizable deep eutectic solvents（PDESs）were designed to prepare"all-in one"transparent conductive elastomers after the process of solvent-free preparation and in-situ photopolymerization.From the design and synthesis of the novel PDESs,optimizing the comprehensive performance of the transparent conductive elastomers and expanding the application of PDESs,this thesis is included as follows:（1）It would breed bacteria and endanger the health of users due to the long-term use of some flexible conductive devices which contacted with the environment or human skin metabolites.Flexible conductive materials with antibacterial properties were required.Based on the demand for antibacterial conductive materials for flexible conductive devices,quaternary ammonium tetramethylammonium chloride with antimicrobial effect was precisely designed and selected as the hydrogen bond acceptor of PDESs system,which could combine with polymerizable acrylic acid and maleic acid to form dynamic hydrogen bonds in the system.The formation of PDESs was characterized by IR,¹H NMR and DSC,suggested that there were hydrogen bonding interactions between components in the system of PDESs.A series of highly transparent（optical transmittance was up to 93%）,stretchable（917%-1025%）,and self-healing（electrical healing efficiency was about 99%within 0.8 s）conductive elastomers with antibacterial effect were obtained through the in-situ photopolymerization.The antibacterial conductive elastomer was used for ionic skin sensor to monitor external stimuli and changes in temperature and humidity.The experimental method provided in this chapter will provide a novel idea for the preparation of antibacterial conductive materials and further broaden the application of PDESs.（2）Mechanical properties,as one of the basic performance indicators of flexible electronic devices,have been the goal needed continuous improvement.To further improve the mechanical properties of the antimicrobial conductive elastomer in the previous chapter,the phytic acid molecule containing six phosphorus hydroxyl groups was introduced to produce a tetramethylammonium chloride-acrylic acid-phytic acid type PDESs system.Taking advantage of inducing dynamic bonds into the elastomeric structure and controlling the crosslinking density of the networks,one of the conductive elastomers（10 wt.%PA）showed both high mechanical strength（the strain was 31.21 MPa and the stress was 3645%）and excellent stretchable properties（up to 3645%）.Further,the conductive elastomer also exhibited excellent transparency（>94%）,favorable conductivity（0.007–0.04 S/m）,and good self-healing capability（electrical healing efficiency of 99%within 0.26 s）.Owing to their smart structure and practical features,these CEs are promising and multifunctional materials for further investigation and use in the fields of advanced sensors and corresponding electronics.（3）The introduction of self-adhesive properties in conductive elastomers can significantly improve the integration capability of flexible electronic devices.The strong self-adhesive capability could reduce the interfacial impedance and prevent it from falling off during tensile deformation.A new type of conductive elastomer was synthesized by the rational design and tuning of hydrogen bond acceptors（choline dihydrogen citrate）and donors（acrylic acid and oxalic acid dihydrate）in PDESs through a rapid UV photopolymerization process.The conductive elastomers have hierarchical hydrogen bonding crosslinking and abundantly dynamic interactions in polymer network,resulting in a wide spectrum of properties such as high optical transparency（transmittance>92%）,stretchability（strain was from 400%to 4600%）,ionic conductivity(0.25-2.6×10^-2 S/m),self-healing（the efficiency was up to 92.5%）and strong adhesion.Since the prepared conductive elastomer can form various interactions between interfaces,it can adhere instantaneously,firmly and long-lastingly to various surfaces.In view of the comprehensive performance,the prepared conductive elastomer can be used as a dry self-adhesive,self-healing sensor for the signal monitoring of volume change or robot motion.Overall,the use of PDESs to prepare conductive elastomers with facile preparation,fast and green features will facilitate the integration and development of flexible electronics in the future.（4）In order to solve the problems of flexible electronics,such as complex preparation,high production costs,and difficulty of waste and recycling,a fully recyclable and self-healing conductive elastomer based on PDESs was reported.By introducing glycerol containing three alcohol hydroxyl groups into the choline chloride-acrylamide PDESs system,more hydrogen bonding crosslinking sites were provided to the system,and the crosslinking density in the polymer network was regulated to prepare a recyclable and self-healing transparent conductive elastomer.Subsequently,the synthesized conductive elastomers have excellent transparency（>92%in the visible range）,tunable mechanical properties（stress was 0.05-3.28 MPa,strain was from 810%to 1470%）,ionic conductivity（0.01-0.04 S/m）,and exceptional self-healing capability（healing efficiency was up to 93%after the third cutting/healing）.And the resultant conductive elastomers can be readily dissolved and regenerated in water.Moreover,the recycled conductive elastomers retain nearly full-featured properties even after five cycles.In addition,the conductive elastomers show diverse sensory capabilities for the recognition of different liquids and the detection of human motions.Therefore,the conductive elastomers in this work will make a significant contribution to the development of multifunctional and recyclable electronics for the achievement of a sustainable future.（5）The implementation and development of green electronic devices combined with natural materials is critical for providing a more sustainable future.Nanocellulose-based transparent conducting material,an important primary component of future green electronics,has been considered one of the most exciting and salient materials in next-generation flexible electronic devices.It remains a challenge to facilely fabricate highly transparent conducting nanopaper with electrical robustness,a necessity as they play quite an important role in the display and/or optically related fields of flexible electronics.In order to expand the application of PDESs system and focus on solving the current problem of serious environmental pollution from electronics,a facile and efficient method based on in-situ photopolymerization of PDESs for the preparation of conductive nanopaper was proposed in this study.The prepared conductive nanopaper has excellent optical properties（optical transmittance was up to 93%）,mechanical properties（stress was up to 12.5 MPa,strain was about 200%）,electrical self-healing（repair efficiency 82.3%）and degradable properties（complete degradation in soil was about 100 days）.In addition,the conductive nanopaper also showed excellent electrical stability and durability.Furthermore,we have demonstrated the practical suitability of the conductive nanopaper through assembly into flexible electroluminescent devices.This study will provide a new efficient preparation process for the development of flexible electronic devices.Furthermore,the use of PDESs combined with nanocellulose paper will play an important role in promoting the development of green flexible electronic devices.