Preparation And Application Of Multifunctional Polyacrylamide Hydrogel-based Sensors

With the rapid advancement of science and technology,the widespread utilization of wearable devices,intelligent robots,and artificial intelligence has propelled the research and development of intelligent sensors into the spotlight.In comparison to conventional rigid sensors,flexible sensors exhibit superior adaptability and flexibility in complex and dynamic environments,catering to diverse applications.Inspired by prevalent deformable structures found in nature,researchers have embarked on investigating and fabricating various selfassembling materials.Among these materials,hydrogels with biomimetic properties and multi-responsive characteristics are considered as ideal candidates due to their ability to mimic biological deformation or shape alteration.Hydrogel-based flexible and wearable sensing materials encompass a variety of sensors that not only detect and quantify different environmental stimuli such as strain,pressure,and temperature but also find extensive utility in personal health monitoring,human motion detection,and electronic skin applications.The distinctive feature of hydrogel materials lies in their capacity for diversified functionality including conductivity modulation,self-healing capability,self-adhesion property enhancement as well as biocompatibility augmentation through alterations in their primary network structure or filler composition.This versatility renders hydrogel-based sensors highly versatile with broad applicability.In this thesis,we design and synthesize a range of multifunctional hydrogel materials,leveraging their distinct properties such as the piezoresistive effect and triboelectric nanogenerator effect.Based on these effects,we fabricate a series of flexible sensors,develop a multi-sensor coupling intelligent system,and construct an optical response self-monitoring soft actuator inspired by bionics.Through our research and development efforts,we successfully achieve functionalities including human motion monitoring,human health monitoring,vehicle status monitoring,as well as intelligent traffic management and control using bionic motion.The main findings are summarized as follows:1.Preparation of multifunctional polyacrylamide nanocomposite hydrogels and their application as strain and pressure sensors: To realize long-term and stable applications of wearable and flexible sensors for motion detection,health analysis and wisdom medication in harsh environments,selfhealing,self-adhesive,electrically conductive and biocompatible polyacrylamide(PAM)nanocomposite hydrogels are fabricated as flexible strain or pressure sensors by in situ polymerization of acrylamide in the presence of polydopamine-modified carbon nanotubes(PDA@CNT)for effectively detecting human motions,identifying materials and their shapes,and transmitting health information.The PDA@CNT/PAM nanocomposite hydrogel exhibits a high self-healing efficiency of 97.3%,excellent biocompatibility,and strong adhesion with substrates based on hydrogen bonding and π–π stacking interactions.Based on the piezoresistive effect,the nanocomposite hydrogel-based strain sensor exhibits a high sense gauge factor of 3.93 at a strain of 400% and responds quickly with a fast response time of 76 ms when detecting human movement.Thanks to the contact electrification and the electrostatic induction,the nanocomposite hydrogel-based pressure sensor can respond to pressure linearly and generate voltage signals in the absence of an additional power supply.Furthermore,the self-powered smart ring made of the silicone rubber-coated PDA@CNT/PAM hydrogel enables efficient and concise information transmission via Morse code.2.Preparation of self-healing nanocomposite hydrogels and research on all-weather self-powered intelligent traffic monitoring system: Selfpowered and sustainable traffic monitoring system is highly required for future urban development.Herein,self-healable piezoresistive sensors and triboelectric nanogenerators(TENGs)are constructed by in-situ polymerization of polyvinyl alcohol-polyacrylamide double network hydrogel in the presence of sodium alginate and tannic acid-modified cellulose nanocrystals(denoted as PPC)for all-weather self-powered intelligent traffic monitoring applications.Because of hydrogen bonding and boron ester bonding,the resultant PPC-based strain sensor can rapidly self-heal and restore its sensing ability within 1 min with a self-healing efficiency of 97.4%.Based on piezoresistive effect,the ions in sodium alginate endow the PPC-based strain sensor with a relatively high gauge factor of 8.39,which can monitor the motion and fatigue of drivers.Based on triboelectrification effect,the PPC-based TENG sensor can detect instantaneous vehicle speed,judge traffic accident liability,evaluate vehicle weight,and alert the driver to prevent accidents caused by drowsy driving.After partially replacing water in the PPC with glycerin,the resulting PPC-based TENG sensor exhibits stable performance at temperatures ranging from-30 to 40 ℃,ensuring its all-weather monitoring ability.The all-weather and selfpowered intelligent traffic monitoring system is promising for ensuring the security of future cities.3.Preparation of photoresponse and conductive hydrogels and application as bionic soft actuators with multiple-freedom of movements for underwater environments: Soft actuators capable of achieving biomimetic behaviors have been widely used in soft robotics and artificial muscles.However,the biomimetic behaviors of most soft actuators usually rely on multiple driving stimulations,which largely limits their widely application,especially in underwater environments.Herein,tannic acid(TA)non-covalently and γ-methacrylic trimethoxysilane(MPS)covalently modified MXene(MPSTA-MXene)using as a photothermal agent,was incorporated into a thermally responsive poly(n-isopropylacrylamide-polyacrylamide)(PNIPAM-PAM)copolymer hydrogel for preparing a photoresponsive nanocomposite(denoted as MNA)hydrogel.The TA effectively preserves the surface characteristic of MXene,while the double bonds on MPS provides covalently bonding between MXene and PNIPAM-PAM,thereby guaranteeing the homogeneous dispersion of MPS-TA-MXene in MNA hydrogel.When exposing at the ultraviolet light,the rod-shaped or starfish-shaped MNA hydrogel-based actuators perform diverse deformations with multiple-freedom in an underwater environment,due to the volume shrinkage of phase transition.Consequently,continuous biomimetic behaviors such as bending,climbing,rolling,and capturing can be easily displayed by the MNA hydrogels,providing a novel orient forward for the exploration of bionic soft actuator underwater.