The Preparation And Properties Of Conductive Self-healing Acrylic Acid/acrylamide Hydrogels

In recent years,conductive self-healing hydrogels have made rapid progress in the application of artificial skin and tissue,wearable electronic devices,individual medical monitoring,and other fields.The important problems restricting the application of conductive self-healing hydrogels are poor compatibility between conductive filler and hydrogel polymer matrix,low rapid self-healing efficiency at room temperature and poor mechanical properties.How to further improve the mechanical properties of hydrogels under the premise of ensuring the excellent electrical conductivity and rapid self-healing performance at room temperature has become an urgent problem.In this paper,acrylic acid(AA)and acrylamide(AM)free radical curing system hydrogels were modified for the traditional hydrogels which could not take into account the excellent conductivity,rapid self-repair at room temperature and high mechanical properties.Firstly,the end group modification of partially reduced graphene oxide(r GO)was carried out.The carboxyl group on the surface of r GO was reacted with the glycidyl methacrylate(GMA)epoxy group,and the free radical polymerizable double bond group was introduced onto the surface of r GO(r GO-GMA)by covalent bonding.The carboxyl group and the polar hydroxyl group on the surface of r GO reacted with the amine group of acrylamides(AM)at high temperature,and the free radical polymerized double bond group was introduced into the surface of r GO(r GO-AM)by means of hydrogen bond.The two-dimensional structure of graphene was embedded into the spatial network of hydrogels through free radical polymerization to synthesize hydrogels with excellent electrical conductivity and certain mechanical strength.The conductivity,tensile stress-strain,rheology,multiple breakage and self-repair conductivity and mechanical properties of the prepared r GO modified acrylic conductive self-repair hydrogel were tested.The conductivity of the hydrogel could reach 20.5S/m,the tensile strength could reach 97 k Pa,and the elongation at break could reach 1500%.The mechanical properties and electrical conductivity of hydrogels can be restored more than 99% after five times of fracture-self-repair process.Based on the above studies,ionic groups were introduced into the synthesis process of hydrogel.Two kinds of ionic monomers,AHSS and SR,were used to introduce the ionic groups of sodium sulfonate and ammonium sulfate into the molecular chain of hydrogel polymer.At the same time,the second crosslinking point was added to the linear molecular chain of the hydrogel by the double-crosslinking monomer HEBa,so that the double-covalent crosslinking was formed between the molecular chains of the hydrogel,which acted synergically with the modified r GO to improve the mechanical properties of the hydrogel.Ion interactions and the introduction of polar double-crosslinked monomers can also improve the self-healing efficiency of hydrogels.Its electrical conductivity was characterized by tensile stress-strain test and rheological test.When the content of r GO-GMA was 5%,the content of ionic monomer was 50%,and the double crosslinked monomer HEBa reached 20%,the elongation at break of hydrogel reached 1805%,and the double crosslinked monomer HEBa was increased to 50%.The tensile strength of the hydrogel reached 1660 k Pa.The mechanical strength and toughness of hydrogels are almost restored to the original state by cyclic compression-unloading tensile test and continuous loading-unloading cycle test.The apparent morphology,electrical conductivity and mechanical properties of hydrogel can be completely recovered at room temperature for 40 s after fracture.It is confirmed that the interaction of ions and many hydrogen bonds as reversible bonding bonds can efficiently consume energy and maintain an efficient internal network structure.The surface modification of nanocellulose CNCs was carried out in order to ulteriorly enhance the strength of hydrogels.The polyethylenimine(PEI)was introduced to increase the polar group content of CNCs.The structure,morphology,and particle size of the modified CNCs were analyzed and characterized.When the content of PEI-CNCs increased from 0% to 5%,the tensile strength of the hydrogel increased from 1.07 MPa to 2.48 MPa,which increased by 131.8%.After 5 times of tensile fracture-self-repair,the tensile strength and electrical conductivity can be restored to more than 99%.PEI-CNCs modified hydrogels showed rapid and repeatable self-healing behavior in rheological properties repair experiments.The self-healing rates of storage modulus and loss modulus of the prepared conductive self-healing hydrogels are more than 99%.The mechanical strength and toughness of hydrogels are almost restored to the original state by cyclic compression-unloading tensile test and continuous loading-unloading cycle test.The electrical conductivity of PEI-CNCS modified hydrogel can reach 28.8s /m.Using this conductive self-healing hydrogel as a sensor to monitor the movement of human joints(fingers,wrists,etc.)and pulse,it shows excellent sensing performance such as high sensitivity,fast response,wide strain range and good stability.It has excellent application prospect in gesture translation,wearable electronic devices and other fields.