Preparation And Flexible Force Sensing Performance Of Stretchable Ionic Condutive Composites

Flexible stretchable ionic conductive sensors have high tensile properties and electrical conductivity,which can convert various stimuli,such as strain and pressure,into electrical signals,and are widely used in human-computer interaction technology,medical monitoring,electronic skin and other fields.Different from traditional electronic conductive materials,ion-conductive composite materials mimic the sensing function of natural skin through ion conduction and become ideal flexible sensor electrode materials.However,complex application scenarios require more excellent performance of ionic conductive materials.At present,ionic conductive materials are mainly divided into ionic conductive hydrogels and ionic gels,but due to their poor mechanical properties,lack of certain strength and toughness,they cannot meet the application scenarios of materials.In general,the covalent crosslinking strategy can significantly improve the mechanical properties of gels,but the lack of effective energy dissipation of covalent crosslinking leads to poor resilience of materials.In addition,it is difficult to recycle and reprocess ionic conductive materials through covalent cross-linking,which leads to resource waste and environmental pollution.Although the ionic conductive composites prepared by non-covalent or dynamic crosslinking can achieve effective energy dissipation,the non-covalent action is weaker than the covalent bond,resulting in low mechanical strength and poor toughness of the ionic conductive composites.At the same time,most ionic conductive composites are not degradable,difficult to recycle and reprocess.Therefore,it is of great significance to develop an ionic conductive composite material with high toughness,high strength,recyclability,degradability and high resilience for the next generation of flexible stretchable ion sensors.In view of this,this paper prepared a biodegradable ionic conductive composite material with high stretchability,high toughness and strength,excellent elasticity and degradability through the vertical composite of degradable polylactic acid material,which is expected to provide a useful reference for the next generation of flexible sensor electrode materials.The main research of this paper is as follows:（1）A novel ionic conducting nanocomposite hydrogel with unique nanocrystalline size and high density hydrogen bond crosslinking was prepared by means of hydrophobic association enhanced by poly（lactic acid）vertical composite crystallization（sc PLA）.Two amphiphilic block polymers,PEG-PLLA and PEG-PDLA,were prepared by ring-opening polymerization of L-lactide（L-LA）and D-LA（D-LA）induced by polyethylene glycol（PEG）at room temperature,respectively.The two polymers were assembled into stable nanomicelles in aqueous solution by means of orthostatic recombination（sc）.The hydrophobically associated hydrogels with high density hydrogen bond crosslinked were prepared by combining the nanomicelles with acrylic acid（AA）by photo-induced one-pot method.Thanks to the sc effect between PLA,the hydrophobic association is further strengthened.The prepared hydrogels have excellent tensile properties（～1000%）,high fracture strength（～500k Pa）and good tensile resilience.In addition,the addition of lithium chloride endows the hydrogels with temperature responsiveness,greatly improves the ionic conductivity of the hydrogels,reduces the freezing point of the hydrogels,thus shows excellent freezing resistance,and still has good flexibility at a low temperature of-20℃.Ionic conducting hydrogels can be assembled into flexible sensors,showing high linear sensitivity（sensitivity factor up to 1.2）and short response time（0.21s）under different strain ranges（0～400%）,while real-time monitoring of complex human movements under different conditions.（2）scPLA-PEG elastomers were prepared by a one-pot method with PLLA,PDLA and PEG as soft segments and hexamethylene diisocyanate and butanediol as hard segments.Thanks to sc PLA nanocrystalline enhancement,sc PLA-PEG exhibits excellent mechanical properties,with high tensile strength of 6MPa,large tensile deformation of 1500%and excellent mechanical resilience.The ionic gel with spider silk structure was prepared by introducing the ionic liquid EMIM:BF₄ into sc PLA-PEG network.The ionic gel showed excellent mechanical properties and high ionic conductivity(3.5×10^-2 S m^-1),making it an ideal candidate material for flexible wearable sensor.The sc PLA-PEG ionic gel has excellent freezing resistance（-30℃）and stable high temperature performance（70℃）due to the low freezing point and difficult volatilization of ionic liquid.Due to the physical cross-linking effect of PLA vertical composite,sc PLA-PEG has excellent recovery performance.Not only can be recovered by hot pressing,also can be recovered by room temperature solvent,recovery efficiency can reach 90%.The strain sensor assembled by sc PLA-PEG/30%ILs has high sensitivity with sensitivity factor up to 1.24.At the same time,it has a wide strain detection range（0～300%）and long cycle stability of more than 300 times.In addition,the strain sensor can be fitted to different parts of the human body,showing reliable repeatability in the detection of movement signals of different parts of the human body,such as knees and fingers.