Preparation And Properties Of Multi-responsive Noncovalent Crosslinked Hydrogels

Hydrogel is a kind of three-dimensional network structure material containing water.It has wide application prospects in driving,sensing,biomedical materials and other fields.With the improvement of performance and function of hydrogel,high-strength hydrogel has become a hot research topic.The poor mechanical properties and fatigue resistance of traditional hydrogels limit the application of hydrogels.Non-covalent crosslinking technology based on macromolecular micelles can improve the mechanical properties of hydrogels,mainly because of three advantages: 1.The micelles are uniformly dispersed in the hydrogel system,and the crosslinking density of hydrogels is very uniform.2.The micelles are connected at both ends of the polymer chain.When the length is enough,the polymer chains are entangled with each other.When hydrogels are subjected to external forces,micelles and surrounding polymer chains cooperate to share forces and avoid stress concentration.3.Micelles with reversible hydrophobic association can dissipate energy as sacrificial units.When the external force is removed,they can self-assemble into micelles,which makes the hydrogels have good fatigue resistance.Intelligent hydrogels with response-driven behavior have been widely synthesized because of their great potential in the fields of artificial muscles,soft robots,actuators and sensors.However,the weak mechanical properties,narrow response range and slow response speed of many responsive hydrogels hinder their further development.Micellar crosslinked hydrogels with excellent mechanical properties can compensate for this.Intelligent hydrogels with functional responsiveness based on high strength hydrogels have more potential.In this paper,the mechanical properties and functional responsiveness of non-covalent crosslinked hydrogels based on macromolecular micelles were studied.Poly(N-isopropylacrylamide)/acrylamide hydrogels with high mechanical properties and poly(dimethylaminoethyl methacrylate)/2-acrylamide-2-methyl-1-propionic sulfonic acid hydrogels were synthesized and assembled into double-layer hydrogels.The performance of hydrogels in actuators.In this paper,the synthesis method of response hydrogel actuator was explored,and the morphology,swelling,mechanical properties and functional responsiveness of the hydrogel were studied.The research is carried out from the following aspects:(1)Synthesis of thermosensitive hydrogels.A tough thermosensitive hydrogel was synthesized by using double bonded triblock copolymer micelles as macromolecular crosslinking agent and N-isopropylacrylamide(NIPAM)and acrylamide(AAm)as monomers.The hydrogel is sensitive to temperature.The obtained hydrogels have a tensile strength of up to 1.6 MPa and a compressive strength of up to 127 MPa,which can be adjusted by changing the formulation.In addition,by changing the molar ratio of NIPAM to AAm,the lower critical dissolution temperature(LCST)of thermosensitive hydrogels can be controlled in a wide range.(2)Synthesis of pH and ion-responsive hydrogels.Ionic hydrogels were synthesized by using double bonded triblock copolymer micelles as macromolecular crosslinkers,dimethylaminoethyl methacrylate(DMAEMA)and 2-acrylamide-2-methyl-1-propionic sulfonic acid(AMPS)as monomers.Hydrogels have strong adhesion and are sensitive to pH and ionic strength.(3)The synthesis of double-layer hydrogel actuators.The second ionic hydrogel was synthesized on the top of the first thermosensitive hydrogel.The double-layer hydrogel is sensitive to temperature,pH and ionic strength.The long strip sample undergoes a rapid reversible shape change from straight line to ring in a few minutes.This multi-response hydrogel device with strong toughness has broad application prospects in soft actuators.