Regulation Of Mechanical Properties Of Hydrogels And Their Applications In Flexible Devices

Hydrogel was composed of hydrophilic polymer networks and a large amount of water,which possess many excellent properties,such as biocompatibility,permeability and tissue-like property,and have potential applications in the field of biomedicine,flexible electronics,sustainable energy and.As a functional material,excellent mechanical properties of hydrogels are a key factor to determine their practical application.In different application scenarios,mechanical properties of hydrogels also have different requirements.Based on it,we adjusts the network of hydrogel through structural design in this paper,so as to obtain a high strength hydrogel material with highly adjustable mechanical properties in a large range.Moreover,we developed the application of hydrogel materials in flexible devices according to the characteristics of hydrogel.The main research contents are as follows:1.We constructed a hydrogel with a double ionically network of acrylic acid-iron ion and chitosan-sulfate.By changing the concentration of ionic solution and monomer,the mechanical properties of hydrogels could be highly adjustable.The hydrogel achieved high strength(5.1MPa)and conductivity(3.04S/m)at the same time.When used as a strain sensor,it could sensitively detect human motion signals,which was superior to most materials applied as flexible device.2.On the basis of the hydrogel with high mechanical properties and electrical conductivity designed in the first part,we further developed a kind of self-healing ionically crosslinked hydrogel.The mechanical properties and ionic conductivity of hydrogels could be easily adjusted by changing ionic solution and monomer concentrations,while maintaining excellent self-healing performance(the self-healing efficiency up to 97.34%).When used as a strain sensor,the self-healing property of hydrogel could greatly extend the service life.3.On the basis of excellent mechanical properties,electrical conductivity and selfhealing properties,we further designed a freeze-resistant hydrogel to improve the environmental tolerance.This hydrogel based on a double ionically cross-linking network,had adjustable tensile properties(1190-1550%),tensile strength(0.96-2.56 MPa),toughness(5.7-14.7 MJ/m3),self-healing properties(the self-healing efficiency up to 83.7%),electrical conductivity(4.58-5.76 S/m)and frost resistance(as low as20℃).When used as flexible devices,it could work well at room temperature and low temperature,which provided a new strategy for the practical application of hydrogel flexible devices.4.The organohydrogel could be regulated to achieve high strain(over 2150%),strength(over 0.5MPa),toughness(over 4MJ/m3),excellent self-healing properties(the self-healing efficiency up to 100%)and frost resistance(as low as-50℃).When used as an electronic skin,it showed multiple responsiveness to multiple signals of tension,compression,temperature,humidity and solvent simultaneously,showing excellent comprehensive performance.The work offered a novel perspective on developing new types of electronic skin.5.By regulating and designing the crosslinking density,selectively covering different concentrations of iron ions on the surface of hydrogel,the hydrogel could be programmed to deform into the designed shape under water.At the same time,the deformation was further restored by the elimination of alkali or glycerin.Based on this deformed hydrogel with high strength,the flexible gripper designed by us could grip heavy objects underwater.The object was more than 1.56 times higher than its own weight,providing alternative materials for the design of flexible grippers.