High-performance Polyaniline-based Conductive Hydrogels As Flexible Mechanical Sensors

In recent decades,flexible sensors have attracted great attention due to their important applications in electronic skin,human health monitoring,soft robotics,etc.Conductive hydrogels based on hydrogel matrix and conductive materials have high stretchability and good biocompatibility,and are ideal materials as a new generation of flexible sensors.The structural tunability of the hydrogel matrix and the diversity of conductive material choices also provide the possibility to fabricate flexible sensors with different functions.Polyaniline（PANI）is easy to prepare and has a unique doping process.Its polymer chain can form a homogeneous network structure with the hydrogel network,which overcomes the uneven dispersion and aggregation of metal materials and carbon materials in the aqueous gel system.Thus,PANI is a good choice for conductive materials.However,its inherent hydrophobicity and mechanical brittleness make it poorly compatible with aqueous hydrogel matrices,affecting the sensitivity and mechanical properties of conductive hydrogels.In this paper,we improved the hydrophilicity of PANI by introducing the amphiphilic substanceβ-cyclodextrin into the system to interact with the aniline host-guest and providing a polymer template for aniline.In addition,metal coordination ions were introduced into the system to design and optimize PANI-based conductive hydrogels from different angles.Two high-performance PANI-based conductive hydrogels were successfully prepared as flexible mechanical sensors.The specific research content are as follows:1.ThehydrogelbackboneP（acrylamide-co-acrylicacid）（P（AAm-co-AA））carryingβ-cyclodextrin（β-CD）was prepared by radical polymerization,and the backbone strength was enhanced by the coordination between Fe³⁺and-COOH.Using the host-guest interaction betweenβ-CD and aniline（ANI）to in-situ polymerize ANI in the pore size ofβ-CD to form conductive network polyaniline（PANI）and obtain the interpenetrating double network conductive hydrogel PANI-P（AAm-co-AA）@Fe³⁺.The amphiphilicity ofβ-CD can improve the poor compatibility of PANI in aqueous gel matrix and improve the conductivity of the hydrogel（2.89 S/m）.The cyclic structure ofβ-CD also protected PANI and improved the cyclic loading of the hydrogel.In addition,the mechanical properties of the hydrogel can be adjusted（ultimate tensile strength:0.0710-0.3054 MPa;fracture strain:145-880%）through the competition of protonation,which can meet the needs of different application scenarios as a flexible mechanical sensor.2.Sodium carboxymethyl cellulose（CMC）and Al³⁺were introduced into the hydrogel network P（AAm-co-AA）,and then the conductive network was filled with CMC as the polymerization template of PANI to prepare the conductive hydrogel PANI-CMC-P（AAm-co-AA）@Al³⁺.Using the electrostatic interaction and coordination interaction between CMC and Al³⁺,as well as entanglement between chain structures to improve the mechanical properties of the conductive hydrogel,making it reach a maximum tensile strain of up to 2100%,which can provide a very broad sensing scope.CMC as a bio-template for the in-situ polymerization of PANI improves the loading of PANI and enhances its dispersion and compatibility in the hydrogel matrix,thereby enhancing the conductivity（3.033 S/m）and linear sensitivity（GF=5.5）of the conductive hydrogel.The high sensitivity enables the flexible sensor based on PANI-CMC-P（AAm-co-AA）@Al³⁺conductive hydrogel to precisely monitor both large movements（wrist,finger bending）and tiny movements（swallowing,speaking）.