Construction Of High-Strength Cellulose-Based Smart Hydrogel And Modulation Of Their Structural Properties

Smart hydrogel is a type of gel with a three-dimensional network,which can rapidly change its volume or physical properties in response to environmental stimuli and have therefore received great attention in fields such as medical tissue and artificial intelligence.However,not only the response performance of hydrogels needs to be considered in applications,but their response rate is also one of the important influencing factors.Therefore,this thesis constructs smart hydrogel 3D networks by using cellulose nanofibres（CNF）,temperature-sensitive polymer poly-N-isopropyl acrylamide（PNIPAM）with conductive filler MXene,as well as constructing anisotropic structures,bilayer structures,to improve their mechanical properties,swelling rate,driving sensitivity and ion transport rate.The main studies are as follows.（1）CNF was used as the first rigid network,and the second network of PNIPAM and the second network of poly（acrylamide-co-acrylic acid）（PAM-AA）were fabricated as the top and bottom layers of the bilayer hydrogel respectively by the interpenetrating network structure method,and then Fe³⁺was cross-linked with to carry out double ions to produce a thermally responsive bilayer double network hydrogel.It was found that the mechanical strength of the bilayer hydrogel increased as the content of CNF increased.At the same time,the driving sensitivity of the two-layer hydrogel was significantly enhanced due to the asymmetric expansion and contraction behavior of the two layers.（2）CNF fibers were prepared as the first rigid network by the polyelectrolyte complexation spinning（IPC）method,followed by the PNIPAM second network and PAM-AA second network by in situ free radical polymerization as the top and bottom layers of the bilayer hydrogel,respectively.The bilayer double network hydrogel has an excellent tensile strength（729.5 KPa）and driving sensitivity,and the hydrogel driver can lift to 70 times its weight in less than 1 min.When the bilayer hydrogel was further cross-linked with Fe³⁺,its tensile strength was up to 3.86 MPa,comparable to the performance of biological tissues.（3）To further enhance the driving sensitivity as well as the interfacial bonding of the hydrogels,thermally conductive fillers（boron nitride BN）and dynamic covalent bonds（borate ester bonds）were introduced into the anisotropically structured bilayer hydrogel.It was confirmed that the addition of BN resulted in a good thermally conductive pathway in the orientation direction of the bilayer hydrogel,resulting in a bending velocity of up to 11（°/s）.At the same time,the dynamic covalent bond borate ester bond can be broken and reorganized at room temperature,which in turn enhances its interfacial bonding force and enables the two hydrogels to be tightly bonded.（4）To further broaden the application area of smart hydrogels and improve their electrical conductivity,conductive double network hydrogels with anisotropic structures were prepared by introducing the conductive filler MXene through IPC spinning.It was shown that the conductivity of the MXene-based conductive hydrogel was significantly increased to 13.08 S/m at 2 wt%Li Cl content due to the directional nano-ion channels derived from MXene to facilitate ion transport.