Preparation Of Low-temperature-resistant Multifunctional Gel And Its Application In Flexible Strain Sensor

Recently,the field of flexible electronics is thriving.In these applications,the flexible sensors have received the widespread attention of researchers.The flexible sensors could convert complex and dynamic deformation into easily collected electrochemical signals,which were used for motion tracking and human health monitoring in real-time.Hydrogel,as a kind of polymer with the three-dimensional cross-linked network using the water as solvent,has significant ductility,flexibility and conductivity.Meanwhile,the modulus of hydrogel is similar to biological tissues and organs.Therefore,most of flexible sensors based on the hydrogels as the critical component were assembled and applied in real life.However,conventional conductive hydrogels will inevitably suffer from inner water evaporation or solidification at high temperatures or subzero temperatures,so the applications of hydrogel were seriously limited.It is a meaningful thing for widening the practical ranges to design the anti-drying and non-freezing hydrogel.Moreover,some reported hydrogels presented the problem of mechanical damage after long-term usage,so the service life of the hydrogels is severely shortened.In addition,the hydrogels will inevitably exposure to aqueous environments（e.g.,raining and sweating）,leading to swelling state and impaired capabilities.Considering the frozen situation of hydrogel under subzero temperatures,we introduced anti-freezing agents in the preparation process of hydrogel in our works,so that conductive hydrogel can be used at low temperatures.For the first work,we designed a non-swelling hydrogel with anti-freezing and tough abilities under aqueous environments.The as-prepared hydrogel could be applied to assemble strain sensors for monitoring the body activities and the strain in the solvents.For the second work,a self-healing organohydrogel was obtained based on the multiple hydrogen bonds,it was assembled to flexible strain sensor for detecting human movement in real time.Meanwhile,it could realize the information recording and erasing by stimulation.The specific work is as follows:1.Low-temperature tolerant and solvent-resistant soft electronic devices have received increasing attention due to their excellent adaptability under multiple environments.The poly（3,4-ethylenedioxythiophene）:poly（styrenesulfonate）（PEDOT:PSS）and zwitterionic betaine（ZB）are introduced into the Al³⁺cross-linked poly-acrylic acid（PAA）networks to construct a multipurpose hydrogel(PAA-Al³⁺/PEDOT:PSS/ZB),which exhibits superior stretchability（1457%）,tensile strength（1.43 MPa）,freeze-tolerance（-35℃）and solvent-resistant capability.Furthermore,a strain sensor with multi-environmental stability is fabricated based on this hydrogel,which could not only accurately monitor the different human motions（finger bending,writing,swallowing,breathing,walking,head-up/down and wrist-up/down）at room temperature,but also reliably distinguish the various mechanical deformations in diverse solvent media（water,cyclohexane and methylbenzene）and harsh climatic condition（-35℃）.In addition,a flexible tube-shaped PAA-Al³⁺/PEDOT:PSS/ZB hydrogel is also successfully developed in the specific reaction mold,which can be utilized as a soft connection for the tap or two severed glass tubes to transport different liquids benefiting from the significant mechanical toughness and anti-swelling property.It is anticipated that the as-prepared hydrogel may be a promising flexible material with multi-environmental stability applying in biomedical devices,soft robotics,electronic skins and wearable sensors under complex environments.2.Smart hydrogels with various stimuli-responsiveness have shown tremendous prospects in the areas of electronic skins,artificial medical organization and soft robotics.Herein,a multifunctional organohydrgel is prepared by introducing polyvinylpyrrolidone（PVP）,acrylic acid（AA）and acrylamide（AAm）into water/dimethyl sulfoxide（H₂O/DMSO）binary solvent system.The introduced PVP and chemical cross-linked P（AA-co-AAm）chains based double network structures and the amount of reversible hydrogen bonds between polymer chains endow the as-prepared organohydrogel with excellent mechanical property（1554%strain）and self-healing capability.Meanwhile,the organohydrogel exhibits extraordinary low-temperature tolerance（-40℃）and long-term anti-drying property（83%moisture retention after 7 days）due to the strong interactions between water and DMSO.Furthermore,the flexible strain sensor based on the organohydrogel displays a wide strain sensing range（0-500%）and repeatable response capability,which can precisely monitor varying degrees of stretching deformations and a series of intricate human movements.Owing to the remarkable freezing resistance and self-healing property,the original and healed organohydrogel sensors still exhibit stable sensing behaviors in freezing environment of-40℃.Noticeably,the obtained organohydrogel can also be served as a special paper to realize the information recording and erasing function at subzero temperatures.These outstanding performances indicate the organohydrogels may be employed as durable and freezing-tolerant smart materials applied in future flexible electronics,soft robots and information platform.