Study On Stretch-resistant PAM/PVP Gel And TCT-HTPB-COOH Elastomer Flexible Strain Sensing Material

Flexible strain sensors are the device that converts external stimuli into electrical signals,and it has bendable and stretchable.There have been a large number of research reports on software robots,biomedicine,and human-computer interaction.The core component of a flexible strain sensor is strain sensing material.However,it is still a great challenge to prepare strain sensing material with tensile resistance and environmental stability.To address the above problems,this paper uses the strategy of the covalent bond and non-covalent bond crosslinking to prepare double-network ionic hydrogels with tensile resistance,water retention,and adhesion,double network glycol organic gels with tensile resistance environment stability,and elastomers with tensile resistance and moisture resistance.The strain sensing materials with different electrical and mechanical properties were prepared by doping inorganic salt solution or nano conductive filler.Firstly,polyacrylamide/polyvinylpyrrolidone(PAM/PVP)dual network ionic hydrogels were prepared by photoinitiated free radical polymerization,by adding crosslinking agent polyethylene glycol diacrylate(PEGDA400)and monomer acrylamide(AAM)into dissolved LiCl and polyvinylpyrrolidone(PVP)aqueous solution.Among them,AAM and PEGDA400 covalent bonds are cross-linked to form a polyacrylamide(PAM)polymer network.The PAM and PVP form a PAM/PVP double network structure of covalent bond cross-linked and physical entanglement.PAM/PVP dual network ionic hydrogel has tensile resistance due to the fracture of the covalent bond crosslinking network and the dissipation of energy of the polymer chain.LiCl doping causes Li+and Cl-to form hydration ions with high bond energy,which reduces the evaporation rate of water molecules and makes ionic hydrogel water retention.Ionic hydrogels have a conductivity of 2.0 S/m and a tensile sensitivity of 2.49 at the 18000%tensile strain range,which is higher than hydrogels in water retention.The ionic hydrogel can be used as a strain sensor to detect limb joint movement,and can also be used as a gel electrolyte for the supercapacitor with 2500%tensile strain and stable capacitance.Secondly,PAM/PVP double network ethylene glycol organogels were prepared by heat-initiated free-radical polymerization.Ethylene glycol was used as the dispersion phase,crosslinking agent PEGDA400 and monomer AAM were dissolved in PVP dispersion with critical entangling concentration.AAM and PEGDA400 covalent bonds were crosslinked to form a PAM polymer network.The PAM covalent bond cross-linking network forms a PAM/PVP dual-network structure with covalent bond cross-linking and physical entanglement with PVP at critical entanglement concentration.Theoretical calculation shows that the physical effective crosslinking density of the PAM/PVP glycol organogels is 1/3 of that of PAM/PVP hydrogels,which is beneficial to the stretching and slippage between molecular chains and makes the double-network glycol organogels tensile resistance.High boiling point and lower freezing point ethylene glycol further improves the environmental stability of ethylene glycol organogels.The tensile strain of ethylene glycol organogels was 21000%and remained constant at-20 and 80℃.Graphene,multiwalled carbon nanotubes,and silver nanowires were doped into ethylene glycol organogels to prepare nanocomposite strain sensing materials.The graphene-doped ethylene glycol organogels showed a stable response signal within the range of 50000 cycles.Multi-walled carbon nanotube doped ethylene glycol organic gel with tensile sensitivity of 3098.99;Silver nanowire doped ethylene glycol organic gel with 22000%tensile strain.These strain sensing materials can be used as strain sensors to detect the movement and deformation of different joint parts of the human body in real-time,showing application potential in wearable.Finally,a new type of TCT-HTPB-COOH elastomer was prepared by using the reaction of melamine and hydroxy-terminated polybutadiene to form the covalent bond cross-linking network.The mercaptoacetic acid was used to form hydrogen bond interaction between molecular chains through click chemical reaction.This structure,based on covalent bond crosslinking and hydrogen bond interaction,gives the TCT-HtPB-COOH elastomer 4200%tensile strain.Spraying multi-walled carbon nanotubes dispersion liquid on the surface of the elastomer,the flexible strain sensing material was prepared.The tensile sensitivity was 2.15 in the range of 3900%tensile strain.In the range of 9000 times of cyclic stretching,it has a stable response signal.This flexible strain sensing material shows moisture resistance when its relative resistance remains constant after 120 min in water.When it is used as a strain sensor to detect human finger bending in water,its relative resistance value is the same as that tested in air,showing a stable motion detection ability in a wet environment.