Preparation And Characterization Of Ionogels Based On Fluoropolymers

Living matter conducts electrical signals mostly using ions,while man-made machines conduct electricity mostly using electrons.Hybrid circuits that combine the distinct ionic and electronic circuits might greatly expand the boundaries of carbon-based life.The development of ionic circuits and devices relies on novel ionic conductors.Ionogels,also known as ionic liquid gels,are an important kind of ionic conductors.Thanks to the high conductivity and stability,ionogels have found wide applications in many ionotronic devices to replace the conductive hydrogels.Currently,it remains an urgent and challenging task to develop multifunctional,high-performance ionogels,which relies on the introduction of new polymeric networks of good compatibility with ionic liquids.In this Dissertation,we developed a novel kind of ionogels based on a fluorinated monomer through simple photo-initiated free radical polymerization.The resulting fluorinated polymeric network was compatible with ionic liquids through the“ion-dipole”interactions,which endows the ionogels with excellent stability.Moreover,by introducing hydrogen bonding interactions for energy dissipation,the mechanical properties of our ionogels based on fluorinated polymers were enhanced.Based on these non-covalent interactions,a physically crosslinked multifunctional ionogel with self-healing capability could be demonstrated.The major contents and conclusions of this Dissertation are briefed as follows:（1）Using a fluorinated monomer,2,2,2-trifluoroethyl acrylate（TFEA）,an ionogel with high transparency（94%）,high mechanical strength（up to 0.69 MPa）,and high stretchability（up to 1493%）was prepared.Such an ionogel also showed high conductivity(up to 3.08 m S cm^-1),good thermal stability,and good resistance towards water and oil.Flexible strain sensors based on this ionogel were fabricated and used to realize reliable real-time monitoring of different human movements both in the air and underwater.（2）Hydrogen bonding interaction was introduced by the acrylamide（AAm）comonomer to effectively strengthen the fluoro-polymer-based ionogels for enhanced mechanical strength and resilience.Using the resulting strong ionogels,a bioinspired flexible capacitive pressure sensor（CPS）was fabricated with a bionic micro-protrusion structure at the electrode/dielectric layer interface.Such CPS device showed an ultra-wide pressure detection range（10 Pa～1 MPa）,good sensing sensitivity(up to 0.802 k Pa^-1),and excellent mechanical stability（over 8000 cycles）.Moreover,the CPS could accurately recognize subtle human physiological signals and distinguish different common objects through hardness identification.An integrated multipixel touch panel based on the CPS exhibited spatial definition and achieved facile input of English alphabets in Morse code using different gestures.（3）A kind of physically crosslinked multifunctional ionogels were prepared via the photo-initiated copolymerization of TFEA and AAm in ionic liquid without any chemical crosslinker.The resulting ionogels possessed a combination of desirable properties,including transparency,high stretchability,solvent and temperature resistance,recyclability,high conductivity,underwater self-healing ability and underwater adhesiveness.The abundant noncovalent interactions including hydrogen bonding and ion–dipole interactions endowed the ionogels with excellent mechanical strength,resilience,and rapid self-healing capability at room temperature,while the fluorine-rich polymeric matrix brought in high tolerance against water and various organic solvents,as well as tough underwater adhesion on different substrates.Wearable strain sensors based on the ionogels can sensitively detect and differentiate large body motions,such as bending of limbs,walking and jumping,as well as subtle muscle movements,such as pronunciation and pulse.In summary,this Dissertation focused on the preparation and characterization of ionogels based on fluorinated polymeric networks.By introducing the fluorinated monomer TFEA,a series of novel ionogels were obtained using the simple photo-polynmerization technique.Seveal types of sensors were also fabricated for reliable and sensitive sensing of human motions or pressure.It is believed that this Dissertation would provide insights for the design of novel ionogels and the development of ionotronic devices with improved performance,and the novel ionogel system would provide the platform for the future development of flexible ionotronics.