| Hydrogel is composed of three-dimensional cross-linked network and a large amount of water.It has soft and wet properties similar to skin,cartilage,muscle and other soft tissues.In addition,according to different structures and compositions,hydrogels also exhibit other properties,such as mechanical flexibility,self-healing,biocompatibility,reversible adhesion,stimulus responsiveness,conductivity,etc.Hydrogel has broad application prospects in tissue engineering,artificial skin,flexible energy storage devices,flexible wearable sensors and flexible actuators.However,there are still some problems in the application of traditional hydrogels in flexible supercapacitors,flexible wearable sensors and flexible actuators.First,most hydrogels used traditionally are not responsive and are only used as electrolytes or signal conversion materials,which makes it difficult to achieve reversible regulation of electrochemical processes.Second,when responsive hydrogels are used in flexible electronic devices or actuators,their response speed and response amplitude are limited,which limits the performances of hydrogel devices.In this paper,N-isopropylacrylamide（NIPAM）and acrylic acid（AA）were used as raw materials to prepare temperature sensitive microgel（MG）through emulsion polymerization.Then MG was introduced into NIPAM and AA copolymer hydrogel network to prepare multiscale temperature sensitive hydrogel（P（NIPAM-co-AA）/MG）.The performances of P（NIPAM-co-AA）/MG hydrogels in flexible sensors,flexible supercapacitors and actuators were explored.It provides new ideas for the development of new gel electronic devices and actuators.The main research results includes:（1）The temperature sensitive microgel was introduced into the temperature sensitive hydrogel network to prepare multiscale temperature sensitive hydrogel（P（NIPAM-co-AA）/MG）.The results showed that the introduction of improved the temperature response rate and amplitude of the hydrogel electrolyte,with the response rate being increased by 87.5%and the response amplitude being increased by 295%.During the heating process,P（NIPAM-co-AA）/MG hydrogels gradually underwent phase transition,the pore structure of hydrogels decreases,and the ion transport process in the electrolyte was weakened.The heat generated in the energy storage process could be effectively absorbed by the volume phase change process of the hydrogel.At the same time,the weakening of the ion transport process can also effectively reduce the heat accumulation and prevent thermal runaway.Due to the reversible temperature sensitivity of the hydrogel electrolyte,the supercapacitor realized controllable energy storage under the switching temperature of 25°C（>VPTT）and 70°C（<VPTT）.The specific capacitance was 9 m F·cm-2 at 70°C and 124.13 m F·cm-2 at 25°C,respectively.In addition,the supercapacitor with hydrogel as electrolyte also has good flexibility.Research has shown that supercapacitors can achieve stable charging and discharging when bent with an increasing angle from 0°to 180°.（2）On the basis of multiscale P（NIPAM-co-AA）/MG temperature sensitive hydrogel,a soft and stretchable P（NIPAM-co-AA）/MG//P（AM-co-AA）hydrogel with double-layered structure was constructed by introducing a poly（acrylamide-co-acrylic acid）（P（AM-co-AA））hydrogel layer.Using two pieces of P（NIPAM-co-AA）/MG//P（AM-co-AA）hydrogel film as electrodes and polyethylene film as a dielectric layer,"sandwich"structured capacitive pressure sensors exhibiting a sensitivity of 3.92 k Pa-1 and a sensing range of 0-7.35 k Pa were constructed.Further research shows that P（NIPAM-co-AA）/MG//P（AM-co-AA）hydrogel can be used to construct piezoresistive pressure sensors.Within the pressure range of 0-0.74 k Pa,the sensitivity can reach up to 27.5 k Pa-1.The sensitivity is 6.28 k Pa-1 between 0.74 and 1.72k Pa.The strain sensor constructed with P（NIPAM-co-AA）/MG//P（AM-co-AA）hydrogel has a sensitivity of 0.15 between 0-100%,Between 100-225%,the sensitivity is 0.39.The response time is 63 ms.Based on the research of basic sensing performance,the applications of hydrogel sensors in human motion detection and wireless wearable sensors are further explored.（3）Based on the study of the mechanical sensitivity of P（NIPAM-co-AA）/MG//P（AM-co-AA）hydrogels,the actuating properties of P（NIPAM-co-AA）hydrogels under different modes of temperature stimulation were studied.When the double-layer hydrogel is placed at a temperature higher than VPTT,the P（NIPAM-co-AA）/MG layer bends and shrinks,causing a rapid and directional bending actuation of the layered hydrogel.The effects of crosslinking agent content in MG and P（AM-co-AA）layers,thickness,width and length of temperature sensitive layer on the actuation performance of layered hydrogels were systematically studied.After introducing MG,the actuation behavior of the double-layer actuator was obviously improved.When the content of crosslinker in P（AM-co-AA）layer decreased from 0.2%to0.1%,the bending rate of layered hydrogel increased by 3.15 times.When the thickness of the thermosensitive layer decreases from 3 cm to 1 cm,the bending rate of the layered hydrogel increases by 2.35 times;When the width decreases from 2 cm to 0.5 cm,the braking time of layered hydrogel increases from 90 s to 60 s;When the length increases from 3 cm to 5 cm,the bending rate of the layered hydrogel increased from 188.5°·min-1 to 466.7°·min-1.Interestingly,the layered hydrogel actuator can be used as an effective actuator to grasp target objects in water. |
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