Study On 3D-printing Construction And Force Sensing Performance Of Polyaniline Composite Hydrogels

Flexible force sensors are capable of converting external stimuli such as mechanical deformations into easily processed electrical signals.They usually have the characteristics of lightweight,high sensitivity and environmental adaptability,which have attracted enormous attention in the field of wearable electronics.Flexible force sensors based on various electro-mechanical conversion mechanisms are mainly categorized into resistive and capacitive modes.Among them,the resistive sensor enjoys the merits of simple manufacture,convenient output and low energy consumption,but it faces shortcomings such as narrow response range and long response time.The capacitive sensor enjoys the merits of extraordinary linearity,fast response and dependable stability,however,its recovery ability and sensitivity are poor.Therefore,the next-generation flexible force sensors will inevitably integrate electro-mechanical conversion materials with comprehensive properties including wide response range,high sensitivity and fast response,but it is still a challenge.Conductive hydrogels generally possess high electrical properties,biocompatibility and tunable mechanical performance,thus becoming an ideal material for assembling flexible force sensors.In accordance with conducting mechanisms,conductive hydrogels are differentiated into ionic conductive hydrogels（ICHs）and electronic conductive hydrogels（ECHs）.The ICHs are ideal soft conductor materials owing to their distinctive advantages such as biocompatibility,stretchability and human tissue-like high ductility.However,high ionic conductivity,large mechanical strength and excellent fatigue resistance are arduous to fulfill simultaneously in the ICHs.The ECHs are remarkably attractive as a noteworthy class of flexible sensor materials on account of tunable mechanical flexibility and high electrical conductivity.Unfortunately,the construction of a three-dimensional conductive network in the ECHs and realizing strong interfacial interaction with the elastic hydrogel network is extremely challenging,which will inevitably lead to a significant reduction in their mechanical strength,toughness and conductivity.Therefore,the design and synthesis of conductive hydrogels with electron/ion dual-conducting networks is a promising approach to improve the mechanical elasticity of conductive hydrogel materials and achieve high conductivity,which is conducive to the construction of flexible mechanical sensors with high sensitivity and wide response range.However,the construction of conductive hydrogel materials with electronic/ion dual conductive network still faces bottlenecks such as lack of efficient preparation methods,poor mechanical flexibility of the product,poor linear response and low sensitivity,all of which greatly hinder the applications of electron/ion dual-conducting hydrogels.This thesis focuses on the design and preparation of polyaniline composite hydrogel materials with electronic/ion double conductive network structure.Through studying the relationship between the composition,structure and interface properties of polyaniline composite hydrogel and its mechanical,electrical conductivity and sensing properties,it has realized the controllable construction of polyaniline composite hydrogel microlattices with excellent 3D printing performance,mechanical properties and sensing properties.The main research work is as follows:1.An intrinsic stretchable polyaniline hybrid hydrogel（PHH）is prepared by a reactive shaping method,which triggers two steps of induction shaping and subsequent in-situ polymerization.First,a high-viscosity precursor solution containing poly（acrylic acid）（PAA）,poly（ethylene oxide）（PEO）and aniline monomers is submerged into an acid solution containing initiators,and gelation is quickly formed due to the formation of dense hydrogen-bonded interactions between the PAA and PEO chains.Second,the initiators in the acid solution facilitated subsequent in-situ polymerization of aniline confined in the PAA/PEO hydrogel network into a three-dimensional polyaniline（PANI）network.Benefiting from the formation of reversible hydrogen bonds and electrostatic interactions between the PAA/PEO and PANI networks,the PHH demonstrates excellent mechanical elasticity,high fatigue resistance and notch-insensitive stretchability.Most importantly,the reactive shaping method enables 3D reactive printing of PHH microlattices（PHHM）with pre-designed structures.The prepared PHHM is used as a highly stretchable conductor to assemble capacitive pressure sensors.The resultant sensors demonstrated high sensitivity of 7.10 k Pa^-1 in a wide detecting range and are capable of detecting complex human motions.2.A polyaniline/polyvinyl alcohol-cellulose nanofiber composite hydrogel material（PANI/PVA-CNF）with electronic/ion dual conductive networks is designed through a one-step freeze-thaw method.Due to the hydrogen-bonded and electrostatic interactions between the PVA-CNF network and the PANI network,PANI/PVA-CNF is effectively damaged and reconstruction through weak interactions during the stretching/compression process,thus leading to effective energy dissipation and good fatigue resistance.The introduction of CNF has greatly improved the viscosity and rheological properties of precursor solution,which is directly utilized as ink for direct ink writing（DIW）3D printing.The as-prepared PANI/PVA-CNF microlattices structure possesses high resolution and skin-like high ductility.When assembled as resistive sensors,the PANI/PVA-CNF accurately distinguishes signals including strain and pressure,displaying high sensitivity,wide linear response,ultra-low detection limit and good cycle stability,and further monitors complex human movements.