Study On Preparation And Deformation Properties Of Responsive Composite Hydrogel

As a kind of hydrogels with typical temperature-responsive characteristics,poly（N-isopropylacrylamide）（PNIPAm）is widely implemented in responsive soft actuators.Aiming at the problems of low structural strength,weak interface bonding strength,insufficient responsive deformation and a single type of response of multilayer responsive hydrogels in application fields such as software actuators.The preparation and deformation properties of responsive composite hydrogel were studied in this investigation.The preparation process of a typical temperature-responsive hydrogel PNIPAm was optimized.A multilayer responsive hydrogel system with excellent interface bonding strength and the characteristic of temperature/near-infrared light response was constructed and one model of soft actuator was established.These results will provide technical support for the preparation about the systems of high-strength hydrogels,multilayer hydrogels and multiple responsive hydrogels.First,based on the temperature-responsive hydrogel PNIPAm,physical crosslinking between Ca²⁺cations and sodium alginate（SA）was introduced to form an interpenetrating network with chemically crosslinked PNIPAm,and then Ca/PNIPAm hydrogels were prepared.The effects of initiation polymerization method,crosslinking agent concentration and SA concentration on the properties of Ca/PNIPAm hydrogels were investigated.The results indicated that the pure PNIPAm hydrogel obtained using thermal initiation polymerization had better swelling and temperature-responsive properties compared to the hydrogel using ultraviolet polymerization.As the concentration of SA was 8 wt%,the Ca/PNIPAm hydrogel had the best mechanical properties,the compressive modulus increased by 10 times as compared with the pure PNIPAm hydrogel and its corresponding elastic modulus increased by47%.Moreover,a soft actuator model was prepared based on annular and tubular hydrogels,which had excellent temperature-responsive property and reversible diameter shrinkage behavior.Second,based on the as prepared Ca/PNIPAm hydrogels with high strength,the temperature-responsive PDMS-Ca/PNIPAm bilayer hydrogel was prepared using surface grafting polymerization method with polydimethylsiloxane（PDMS）as the substrate material.Molecular structure,surface morphology,mechanical properties and temperature-responsive properties were characterized.The effects of substrate properties,concentration of pretreatment solution and monomer concentration on the properties of PDMS-Ca/PNIPAm bilayer hydrogel were explored.The results indicated that the higher concentration of benzophenone（BP）provided higher structural strength for the PDMS-Ca/PNIPAm bilayer hydrogel,but its temperature-responsive properties were reduced.The mechanical properties and temperature-responsive properties of PDMS-Ca/PNIPAm bilayer hydrogel could be improved by increasing the concentration of NIPAm.In summary,when the concentration of BP was 5 wt%and the concentration of NIPAm was 20 wt%,the PDMS-Ca/PNIPAm bilayer hydrogel has excellent mechanical properties and temperature-responsive properties which can realize the temperature-responsive characteristic of large reverse bending.Finally,based on the as prepared PDMS-Ca/PNIPAm bilayer hydrogel,photothermal agent molybdenum disulfide（MoS₂）was introduced into the hydrogel layer to prepare PDMS-MoS₂/Ca/PNIPAm bilayer hydrogel with temperature and light responsive properties.Molecular structure,surface morphology,mechanical properties,temperature and light responsive properties were characterized.The effects of MoS₂ concentration on the properties of MoS₂/Ca/PNIPAm hydrogel and PDMS-MoS₂/Ca/PNIPAm bilayer hydrogel were explored.The results indicated that the introduction of photothermal agent MoS₂realized the near-infrared light responsive properties of the bilayer hydrogel.The higher concentration of MoS₂expended the pores in the hydrogel,and the mechanical properties of MoS₂/Ca/PNIPAm hydrogel and PDMS-MoS₂/Ca/PNIPAm bilayer hydrogel were reduced,but their temperature-responsive properties were improved.The increase of MoS₂ concentration was helpful to improve the light responsive properties of the hydrogel.When the concentration of MoS₂was7.5 mg·m L^-1,PDMS-MoS₂/Ca/PNIPAm bilayer hydrogels had the best temperature and light responsive properties which can realize the temperature and near-infrared light responsive characteristic of large reverse bending.These results provide valuable insights into the engineering application of high-strength and multiple response hydrogel system.