Construction Of Multifunctional Gels Based On Dynamic Cross-links And Their Applications In Flexible Electronics

Hydrogels have been widely investigated in flexible electronics due to their mechanical flexibility,conductivity and biocompatibility.However,the existing hydrogel materials still have problems such as poor mechanical strength,freeze at low temperature and serious water loss,which seriously restrict their applications in flexible electronics.The development of multifunctional hydrogels with high mechanical properties,good conductivity and wide operation temperature range is of great significance for the progress of hydrogel-based flexible electronic devices.In addition,the integrated hydrogel-based flexible electronic equipment will inevitably suffer from severe mechanical stress or deformation.Thus,maintaining stable electrochemical performance in the dynamic deformation process or restoring working ability after self-healing can greatly improve the practical application value of hydrogel-based flexible electronic devices.Therefore,dynamic cross-links with energy dissipation and self-healing ability were used to construct multifunctional hydrogels is of great significance for the development and practical application of hydrogel based wearable electronic devices.Herein,two kinds of multifunctional hydrogels were constructed based on dynamic chitosan physical network and dynamic multiple hydrogen bonding,and their applications in flexible energy storage,sensing,information storage and other fields were studied.The main research contents are as follows:（1）A highly mechanical,ionically conductive,anti-freezing multifunctional chitosan/poly（acrylamide-co-acrylic acid）（CS/P（AM-co-AA））DN hydrogel was prepared by using a salt solution immersion strategy crosslinking CS/P（AM-Co-AA）composite hydrogel.The CS/P（AM-co-AA）DN hydrogel,acted as flexible electrolyte,was assembled into mechanical reliable and high-performance supercapacitors.The immersion strategy not only formed a dynamic crosslinked chitosan physical network,which gave the hydrogel excellent mechanical strength and significant anti-softening properties,but also introduced a large number of ions which gave the hydrogel excellent ionic conductivity(4.8 S m^-1 at room temperature and 3.6 S m^-1 at-20 ^oC)and low temperature resistance（<-40 ^oC）.The flexible all-solid-state supercapacitors assembled by hydrogel electrolyte,MXene film electrode and carbon nanotubes（CNTs）film collector exhibited excellent electrochemical performance in a wide temperature range(area specific capacitors at room temperature and-20 ^oC were 297 m F cm^-2 and 150.0 m F cm^-2).The supercapacitors exhibited remarkable structural reliability and electrochemical stability under multiple severe damages.Even upon consecutive 3 d of trampling,the supercapacitor still delivered an unimpaired capacitance and long cycle life.The self-powered sensing device was assembled by CS/P（AM-Co-AA）DN hydrogel-based supercapacitor and sensor,which can sensitively monitor various human movements in real time,demonstrating the great application prospect of CS/P（AM-co-AA）DN hydrogel in the field of high-performance flexible electronics.（2）A poly（acrylic acid-co-N-acryloyl glycinamide）（P（AA-co-NAGA））organohydrogel with self-healing,self-adhesive,anti-freezing and anti-drying perfomances based on dynamic multiple hydrogen bonds was prepared through a simple one-pot process,and further applied in the fields of flexible information storage,flexible sensing and energy harvesting.The high density hydrogen bond between bisamide and carboxyl group in the polymer network and the hydrogen bond between the polymer network and glycerol synergically improved the mechanical properties of P（AA-co-NAGA）organohydrogel（tensile strength:100.2 KPa,elongation at break:1034%）.The unique structural design endowed P（AA-co-NAGA）organohydrogel with excellent self healing（24 h,healing efficiency of 97%）,self-adhesive,conductive and anti-drying performances.The P（AA-co-NAGA）organohydrogel can be utilized as a flexible information storage device to achieve information writing,reading and erasure.The P（AA-co-NAGA）organohydrogel can be used as a wearable sensor to monitor subtle facial expression changes and human joint movements sensitively.Moreover,The P（AA-co-NAGA）organohydrogel can be used to construct flexible triboelectric nanogenerator（TENG）to achieve effective energy collection with open circuit voltage(V_OC),short circuit current(I_SC)and short circuit transfer charge(Q_SC)of 87 V,650 n A and 28 n C,respectively.This work will provide a new avenue for the design and development of self-healing hydrogel-based flexible electronic devices.