Study On The Preparation And Functional Properties Of Polyacrylamide/Sodium Alginate-based Conductive Hydrogel

Conductive hydrogel palys the role of flexible conductive substrate with its excellent tunable electrical and mechanical properties,acting as a bridge to express strain information in the form of electrical signals,which can be used in wearable strain sensors to monitor human movement.Sodium alginate is a natural polysaccharide and the poor mechanical properties of a single sodium alginate hydrogel do not meet the working requirements of strain sensors for flexible substrate movement.In this paper,acrylamide（AM）and sodium alginate（SA）are used as raw materials to prepare chemically cross-linked and physically cross-linked polyacrylamide/sodium alginate-based conductive hydrogel through free radical initiation and hydrophobic interaction,respectively.Its flexibility,conductivity,fatigue resistance and strain sensitivity are also investigated.Finally,it is assembled into strain sensors and successfully used for human movement monitoring.The main research contents are as follows:（1）First,chemically cross-linked polyacrylamide/sodium alginate（PAM/SA）semi-interpenetrating network hydrogel is prepared by free radical polymerization using N,N’-methylenebis（acrylamide）（MBA）as the chemical cross-linking agent,followed by immersion in 0.1 mol/L calcium chloride（Ca Cl₂）solution for 2 h to obtain PAM/SA-Ca²⁺double network conductive hydrogel.Ca²⁺can form an ionic cross-linking network with the carboxyl group of the sodium alginate chain and achieve ionic conductivity through directional movement.The results show that the PAM/SA-Ca²⁺double network conductive hydrogel has the highest tensile strength（314 k Pa）and toughness（1.28 MJ/m³）,elongation at break of 749%and modulus of90 k Pa when the AM content is 8 g,the SA content is 0.6 g and the MBA content is 0.004 g.At this time,the conductivity of the hydrogel is 0.92 S/m,which is nearly 74%higher than that before immersion,and it has stable electrical performance,electrical recovery（electrical recovery response time of 6.02-8.08 s）,strain sensitivity（the sensitivity factor（GF）is 2.57within the strain range of 0-400%）.Finally,it is assembled into a strain sensor to successfully monitor the movement of human finger,wrist and elbow.（2）Physically cross-linked poly（acrylamide-stearyl methacrylate）/sodium alginate（P（AM-SMA）/SA）hydrophobic association conductive hydrogel is prepared by combining hydrophobic monomer stearyl methacrylate（SMA）,surfactant sodium dodecyl sulfate（SDS）and electrolyte sodium chloride（Na Cl）through hydrophobic interaction.The PAM network and the interspersed SA network could form hydrogen bonds to strengthen the internal forces of the hydrogel,where the PAM network is constructed by hydrophobic association micro-regions containing the electrolyte Na Cl act as physical cross-linking points.The results show that when the AM content is 8 g,the SA content is 0.2 g and the SMA/AM molar ratio is 2%,P（AM-SMA）/SA hydrophobic association conductive hydrogel has the best tensile properties（tensile strength of 493 k Pa,elongation at break of 761%,modulus of 45 k Pa and toughness of1.52 MJ/m³）and electrical conductivity（conductivity up to 1.43 S/m）,and shows good fatigue resistance,compression resistance,and self-recovery.The influence of soaking metal ions of different valence(Na⁺,Ca²⁺,Fe³⁺)on the compressive and conductive properties of hydrogel is discussed,and the results show that the strongest binding degree between Fe³⁺and carboxyl groups,and the hydrogel soaked with Fe³⁺has the highest compressive strength（981 k Pa）and electrical conductivity（1.54 S/m）.（3）The interaction between multi-walled carbon nanotubes（MWCNTs）and SA can not only solve the problem of poor dispersion of MWCNTs in aqueous solutions,but also facilitate the construction of homogeneous electron-conducting pathways.Poly（acrylamide-stearyl methacrylate）/sodium alginate/multi-walled carbon nanotubes（P（AM-SMA）/SA/MWCNTs）hydrophobic association conductive hydrogel with improved mechanical and electrical conductivity is prepared by introducing conductive carbon nanomaterial,MWCNTs,into the P（AM-SMA）/SA hydrophobic association conductive hydrogel.The results show that when the AM content is 8 g,the SA content is 0.2 g,the SMA/AM molar ratio is 2%and the MWCNTs content is 0.03 g,the hydrogel has the best mechanical properties（the maximum tensile strength of 636 k Pa,the elongation at break of 908%,the modulus of 62.9 k Pa,and the toughness of 2.3MJ/m³）,and shows good fatigue resistance,self-recovery,and compression resistance.When MWCNTs content is 0.09 g,the hydrogel has the best electrical conductivity（conductivity up to 1.76 S/m）,electrical recovery（electrical recovery response time of 4.07-5.42 s）,electrical stability and strain sensitivity（the sensitivity factor（GF）is 2.81 within the strain range of0-500%）.The strain sensor assembled by the hydrogel has reliable strain sensitivity,stability and fatigue resistance,and successfully realizes the monitoring of human finger,wrist and leg movements.