| As a functional material,bamboo/wood biomimetic materials with high value utilization inspired by the structure,shape and behavior of natural animals and plants,which have been widely used in seawater desalination,photocatalysis,electromagnetic shielding and other fields.However,due to the limitations of structural design and unitary performance,the bamboo/wood biomimetic materials have poor intelligent response and movement flexibility so that they are difficult to achieve deformation and movement under external stimulation,which limits their application and development in the direction of intelligent systems.In this dissertation,a flexible,multi-functional anisotropic bamboo/wood composite hydrogel actuator that can deform and move under external stimuli(such as temperature,light,p H,etc.)has been constructed through combing natural bamboo/wood and stimulus responsive deformable hydrogels.Firstly,the performance of bamboo/wood composite hydrogel actuators were compared to confirm that bamboo was the best biological template.On this basis,the influence of bamboo and hydrogel on the performance of the actuator was revealed by adjusting the parameters of bamboo based composite hydrogel actuator.Furthermore,the introduction of functional materials endowed the actuator with remote control and multiple stimulus response performance,expanding its application in the field of intelligence.In addition,Euler-Bernoulli beam theory and finite element simulation were used to analyze and verify the mechanism of the shape deformation of the actuator,achieving an organic combination of theory and experiment.The main research contents and results are as follows:(1)The radial section of basswood and tangential section of bamboo were selected as biological templates respectively.Bamboo/wood composite hydrogel actuators were prepared by combing bamboo/wood slices with poly(N-isopropylacrylamide)(PNIPAM)hydrogel through UV in-situ polymerization,and the properties of the two were compared.The results showed that the response/recovery speed(76.1°/s,1.3°/s)and bending angle(533°)of bamboo/PNIPAM composite hydrogel actuator were better than those(42.4°/s,1.1°/s,360°)of wood/PNIPAM composite hydrogel actuator under temperature stimulation,which was mainly due to the obvious bilayer structure of bamboo/PNIPAM composite hydrogel actuator.In addition,the bamboo/PNIPAM composite hydrogel actuator also had advantages in tensile strength(2.7 MPa)and complex deformation,which was mainly related to the strict longitudinal arrangement of bamboo cells.Finally,the possibility of bamboo/PNIPAM composite hydrogel actuator assembling smart devices was explored by fabricating a manipulator that can grasp and release heavy objects.(2)The influence of bamboo and hydrogel parameters on the performance of bamboo/PNIPAM composite hydrogel actuator was explored.The results showed that the variable thickness of bamboo and hydrogel can endow the actuator excellent and adjustable bending angle and response speed(response speed 917°/s),which was mainly related to the driving force of the hydrogel and the bending modulus of bamboo.The different elastic modulus of bamboo in both vertical and parallel fibers also engendered texture-dependent complex and controllable deformation of the actuator.The corresponding relationship between the shape deformation of the actuator and the material thickness(orientation)was established through mechanical analysis,which effectively revealing the working mechanism of the actuator.At the same time,finite element simulation was used to predict and verify the shape deformation of the actuator,enhancing the reliability of the experimental results.In the whole system,the interface between bamboo and hydrogel was very close because of the mechanical interlocking structure and hydrogen bonding between them.Based on the advantages of complex deformation,ultra-fast actuation speed and high driving force,the potential application of actuator in the field of biomimetic driving was further explored.(3)A near infrared(NIR)light responsive Bamboo/Nigrosine/PNIPAM composite hydrogel actuator was prepared with nigrosine as the carrier,which realized the remote-control performance.The results showed that the photothermal conversion performance of the nigrosine/NIPAM mixed solution and nigrosine/PNIPAM composite hydrogel was excellent(the photothermal conversion efficiency was 81%),and the photothermal properties were positively correlated with nigrosine content and the NIR light power.The actuator showed variable driving behavior in water and air because of the controllability of NIR light power,irradiation mode,irradiation time and working environment.When the NIR light power increased to 2.0 W,the bending angle and bending speed of the actuator was 360° and 36°/s,respectively,which is mainly related to the better photothermal performance caused by higher NIR light power.In addition,the actuator could also realize the construction of smart switch,manipulator,and biomimetic actuator that move freely on the water surface.(4)The double active layer Nigrosine/PNIPAM/Bamboo/PAAc composite hydrogel actuator(NPBP composite hydrogel actuator)was prepared by introducing p H responsive polyacrylic acid hydrogel(PAAc hydrogel)through two-step polymerization,which overcame the defect of bamboo-based actuator that the stimulus response performance was too concentrated.The results indicated that the actuator exhibited bidirectional bending performance in Na OH and HCl solutions,and its bending angle and bending speed significantly improved with increasing solution concentration.The existence of double active layers endowed NPBP composite hydrogel actuator with multiple response performance.When the NPBP composite hydrogel actuator was placed in a complex environment(temperature/p H,NIR/p H),the bending angle and direction of the entire actuator depend on the driving force of the active layer.In addition,the good coordination performance between two active layers can not only promoted the complex deformation of NPBP composite hydrogel actuator,but also made it have potential application value in the field of pattern design and biomimetic driving. |
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