Study On The Responsive Conductive Hydrogels And Its Applications For Artificial Synapses

Flexible electronic products,with the characteristics of flexibility,portability and wearability,greatly expand the applicable environment for electrical devices,and also promote the development of functional materials.Ionic hydrogels have become a kind of important conductive functional materials by virtue of the characteristic of ionic transmission of electrical signals.Also,relying on the three-dimensional network structures with rich functions,ionic hydrogels obtain excellent mechanical properties,such as flexibility,extensibility and self-healing properties.Therefore,ionic hydrogelbased functional devices such as conductors,sensors and soft robots have become an important development direction.However,traditional semiconductor devices can not only realize information sensing and recognition by controlling the migration of electrons or holes,but also perform intelligent information processing and storage to show brain-like computing ability,which poses a higher challenge to the development of electrical functions in hydrogels.The biological nervous system relies on the directional migration of ions to achieve efficient information processing.Inspired by this,this paper designs supramolecular interactions or dynamic covalent bonds in the hydrogels to control the migration of ions and regulate the electrical signals of hydrogels,so that it can simulate the characteristic of biologicial synaptic information processing,showing the ability of intelligent feedbacks for environmental information.Chapter 1,Introduction.Starting from the application of flexible electronic devices,this paper expounds the development status and design ideas of flexible electronic devices,and leads to the application potential of conductive hydrogels in the field of flexible electronics.Combined with the charge transfer principle of conductive hydrogel,the control means of the electrical signal in ionic conductive hydrogel and its application in the field of flexible electronics are emphatically introduced.Meanwhile,the limitations of hydrogel materials in realizing bio-inspired information processing ability are analyzed.Subsequently,the thesis proposes the idea,research content,and significance of this article.In chapter 2,we obtained a composite hydrogel that can change its conductivity under near-infrared light stimulation,which is realized through integrating thermally responsive ionic supramolecular assemblies and photothermal materials in the hydrogel networks.The principle of the conductivity change of the hydrogel is that the near infrared light is converted into heat by the photothermal materials,which stimulates the disassembly of the ionic assemblies and causes the increase of the concentration of mobile ions.This feature can be used to effectively simulate the information processing mode between neurons in organisms,which is similar to the phenomenon that action potentials stimulate the release of neurotransmitters for modulating the postsynaptic membrane potentials.This hydrogel is used as an information processing element to simulate the synaptic functions,which is combined with the robot arm to construct a spontaneous perceptual feedback system.The hydrogel can automatically recognize the external optical signals and regulate the movement of the robot arm with a behavior similar to the "learning-experiences" behavior of the organism.In chapter 3,a photo-responsive ionic hydrogel with mechanical durability is designed by using photothermal materials,thermal responsive ionic supramolecular assemblies and a self-healing network.The hydrogel can convert near-infrared light energy into heat by using the photothermal materials for stimulating the disassembly of the assemblies in the hydrogel into mobile ions and generating controllable electrical signals.Therefore,hydrogels can be used to simulate the potential changes of postsynaptic membrane caused by the release of neurotransmitters.The hydrogel can still maintain stable synaptic functions during different conditions,including static or dynamic stretching and mechanical destruction.In this principle,we use the hydrogel as an information processor to simulate Pavlov’s conditioned reflex activity,showing good associative learning ability.In chapter 4,we designed a photo-responsive ionic hydrogel and explored its application potential in biomimetic image processing by doping photoacid molecules into a hydrogel.Under the radiation of UV light,the photoacid molecules in the hydrogel release protons through isomersation reaction,thus regulating the conductivity of the hydrogel.Then,we use optical pulses to simulate the action potentials for stimulating the hydrogel to change its conductivity,so as to simulate the changes of the postsynaptic membrane potentials caused by the release of synaptic neurotransmitters.Finally,we patterned the hydrogels as an array to simulate the image recognition ability of the biological vision system.The hydrogel array can effectively recognize and store the "T"-patterned information,which shows different information storage capabilities at different temperatures.