Study On The Preparation And Multiple Stimulus Response Of Flexible Self-powered And Multilayered Electronic Skins

Skin is the largest organ of the human body.It is the physical barrier between the human body and the external environment,at the same time with highly sensitive touch,vibration,humidity and temperature perception ability,to provide the human body with an excellent multi-functional sensor network.Electronic skin?E-skin?is a flexible electronic interface based on bionics,which can reproduce the different shapes and textures of biological skin to recognize external materials,and perceive the changes of pressure,touch,humidity and temperature.It has a variety of potential applications in intelligent robots,human-computer interaction equipment,health monitoring and other fields.However,it remains a huge challenge to integrate high sensitivity,low detection limit,large stretch and multiple stimulus response ability into a single electronic skin.Future opportunities lie in the creation of highly intelligent electronic skin that can sense changes in a variety of external environments,and the rapidly growing innovations in this area will have important implications for the future of science and human life.We fabricate a tunable and nacre-mimetic multifunctional e-skin with a variety of stimulation perception ability,and tunable performance of self-supply flexible electronic skin based on multilayered silver nanowires?AgNWs?/reduced graphene oxide?RGO?conductive network and stretchable TPU mats.We studied the relationship between the structure and performance of the E-skin,and respectively explored the sensitive response behavior,response mechanism and practical application of the electronic skin to stretching,bending and humidity stimulation.In addition,the applications of the electronic skin in triboelectric nanogenerator?TENG?and self-powered tactile sensors were investigated.Specific research contents are as follows:1 Study on the structure design of electronic skin and its influencing factors?1?Inspired by the“brick and mortar”layered architecture of nacre,the equipment diagram and the schematic illustration of fabricating our E-skin:?i?20?m-thick mats are firstly prepared by electrospinning;?ii?high quality AgNWs?diameter of?100 nm and length of?100?m?and RGO sheets?the average size of a RGO sheet is 1.1-1.5?m?are sprayed onto the prepared TPU mat;?iii?another layer TPU mats are prepared to cover the AgNWs/RGO;?iv?different AgNWs/RGO conductive layers of e-skins are designed and constructed to imitate the nacre structure.?2?The effects of AgNWs and RGO content and number of conductive layers on the structure and conductivity of electronic skin are investigated from the microscopic morphology.When the content of AgNWs/RGO is greater than 0.011 g/cm²,the adhesion stability of multilayer structure is damaged.The conductivity of electronic skin is directly proportional to the content of AgNWs and the number of conductive layers,and the elongation at break is inversely proportional to the number of conductive layers.?3?The surface,cross section and microstructure of the 8-layer AgNWs/RGO conductive network with AgNWs content of 50%electronic skin?E-skin-8?are investigated in detail.The TPU fibrous mats in the electronic skin is firmly combined with AgNWs/RGO,and the conductive network is constructed perfectly.In addition,the fibrous mats that makes up the electronic skin is loose and porous and can easily pass through water vapor?57.6%at 2 h at 95oC?,maintaining good air permeability.2 Study on the sensitivity of tensile deformation and bending deformation of E-skin-8?1?The modulability of electronic skin in response to tensile strain is studied.By changing the ratio of RGO to AgNWs,the strain detection range of the electronic skin can be adjusted in the range of 3-200%.By changing the number of AgNWs/RGO conductive layers,the detection range of the electronic skin can be adjusted within a range of 46-200%.This regulation provides a new way to solve the contradiction between responsivity and detection range in strain sensitivity.?2?The tensile strain response behavior of E-skin-8 is studied in detail.The electronic skin achieved ultra-high strain detection range?200%?,ultra-low response limit?0.1%?,high sensitivity?sensitivity factor,GF=1902.5?,rapid response time?20 ms?and excellent durability?11000 cycles of stretch/release test?.By observing the microstructure during the tensile process,we constructed the evolution process of the conductive network of"microfissure-AgNWs bridge-island structure".?3?The sensitivity of E-skin-8 to bending deformation is investigated.The electronic skin was highly sensitive to 0-80%bending rate and had good durability?1000 bending cycles?.In addition,we explained the bending response mechanism by studying the changing behavior of E-skin-8 resistance,which has certain enlightening significance for the bending sensitive sensor.?4?The application of E-skin-8 in human movement and health monitoring is studied.The electronic skin can not only monitor the movement of a single joint in real time,but also simultaneously monitor the combined movement of multiple joints?such as playing badminton?.In addition,E-skin-8 can monitor the movements of human facial muscles,the back of the neck and vocal cords,showing promising results in facial expression,body language and voice monitoring.More importantly,E-skin-8 can sense the weak pulse of the human body,which has been widely used in the fields of health care and human-computer interaction.3 Study on the sensitive behavior of E-skin-8 to humidity?1?The sensitivity of E-skin-8 to humidity is tested by simulating different humidity environments.Under 85%RH,the electrical resistance of the electronic skin changed by 4%,showing excellent sensitivity.In addition,the adsorption and desorption times of e-skin-8 on water molecules were 13s and 14s respectively,showing excellent rapid sensitivity.?2?The mechanism of electronic skin moisture sensitivity is investigated from the microstructure.The loose and porous TPU fiber membrane allows water molecules to pass freely.The hydrophilic graphene conductive layer can quickly absorb water molecules and improve the response time to humidity.Due to the multi-layer structure of conductive layer,RGO has a large area and space for desorption of water molecules,which greatly reduces the recovery time.?3?The application of E-skin-8 humidity sensitive behavior is explored.The electronic skin can monitor air humidity and can be easily attached to a mask to monitor human respiration.More importantly,the electronic skin can detect the humidity of the finger at a distance of 5 mm,so we prepared the E-skin-8 sensor array,which has great application potential in the field of non-contact sensing and control.4 Research on E-skin-8 as stretchable triboelectric nanogenerator?STENG?power supply performance and as self–powered tactile sensor?1?The porous,rough and highly stretchable TPU fibrous mats created the conditions for the preparation of STENG.We studied the electronic skin energy,E-skin-8?4 cm²?can provide ultra high voltage?202.4 V?and a large instantaneous power density?6m W/m²?,also showed good stability work cycle?10000 times?,in addition,the electronic skin?100 cm²?electricity generated at work can light 120 LED lights,can be used as an efficient can strain energy supply device.?2?We have studied the power supply capacity of E-skin-8 under tension.The electronic skin has high efficiency of power supply under 100%strain and stable charge output under ultra-high tensile deformation?200%strain?.After 1000 stretching cycles of 200%strain,the E-skin-8 conductive network is still intact,and the generating capacity is almost the same as before the stretching.?3?The relationship between the voltage generated by E-skin-8 and the friction pressure was studied.It was found that the electronic skin possessed highly sensitive tactile perception(78.4 k Pa^-1)and rapid response to pressure?1.4 ms?.In view of this,we prepared the E-skin-8 self-powered tactile sensor array,which can not only sense the pressure of finger,but also sense the motion track of finger.This super-stretchable electronic skin and energy conversion system shows a good application prospect in the fields of Internet of things,soft robots and human-computer interaction.