Construction And Sensing Performance Of High-Mechanical And Freezing Tolerant CS/P(AA-co-AM) Double-network Hydrogel

Hydrogels,with three-dimensional network structures,are prepared from hydrophilic molecules through physical or chemical cross-linking.Hydrogel has rich moisture content,good biocompatibility and water-retaining property,which has great potential application value in artificial soft tissue,flexible sensors,drug carriers and intelligent robots.However,conventional hydrogels have low mechanical strength and poor freezing resistance,which greatly limits their applications.At present,flexible sensors based on hydrogel materials are widely studied,but most hydrogel sensors have the problems of single monitoring type and limited monitoring range?deformable range and temperature range?,which limits the application of hydrogels-based sensors.In this study,two kinds of high-mechanical properties and freezing tolerant chitosan/poly?acrylic acid-co-acrylamide?double-network hydrogels were fabricated by simple and general salt solution immersion method,and studied the application in flexible sensors.The specific research contents are as follows:?1?Construction and properties of high-mechanical and freezing tolerant chitosan/poly?acrylic acid-co-acrylamide?ion-covalent double-network hydrogel?DN-Sul gel?.First,a one-pot method was used to prepare a chitosan/poly?acrylic acid-co-acrylamide?composite hydrogel based on covalent bond and hydrogen bond,and then the composite hydrogel was immersed in Fe₂?SO₄?₃ to obtain the ion-covalent double-network hydrogel.Copolymerization of acrylic acid and acrylamide formed a chemical cross-linked network,and the chitosan ionic network is a physical cross-linked network.The two networks coordinate with each other to give DN-Sul gel outstanding mechanical properties?tensile strength:2.45 MPa,elastic modulus:0.49 MPa,tensile strain:540%and toughness:6.79 MJ/m³?.The introduction of chitosan ionic network and ionic coordination(CO₂LFe^III)endowed the hydrogel with self-recoverability,self-healability and softening resistance.The mechanical performance of hydrogel was readily adjusted in a large range.In addition,the ions in hydrogel can inhibit the aggregation of water molecules,and weaken the hydrogen bonding between water molecules,leading to excellent antifreeze performance?-20 ??of the hydrogel.?2?Construction and sensing performance of a high-mechanical,anti-freezing conductive chitosan/poly?acrylic acid-co-acrylamide?chain entanglement-covalent double-network hydrogel?DN-Cl gel?.The obtained chitosan/poly?acrylic acid-co-acrylamide?composite hydrogel was immersed in Fe Cl₃ solution to fabricate a chain entangled-covalent double network hydrogel with excellent mechanical property,anti-freezing property and ion conductivity.Compared with DN-Sul gel,the DN-Cl gel possessed a denser network structure and exhibited superior mechanical properties?tensile strength:6.09 MPa,elastic modulus:2.12 MPa and Fracture toughness:15.93 MJ/m³?and low temperature tolerance?-25 ??.In addition,the migration of free ions in DN-Cl gel rendered hydrogels good ionic conductivity.The sensor assembled from DN-Cl gel can monitor stretching,compression and different bending angles,as well as human motion,with high sensitivity?GF=6.60 at?_t=400%?and cyclic stability?300 cycles?.It is worth noting that DN-Cl gel can still maintain outstanding mechanical flexibility and ionic conductivity at low temperatures,therefore the sensor still displayed high sensitivity?GF=3.8 at?_t=280%?at-20 ?,which is superior than that of most conductive hydrogels at low temperatures.