Study On The Response To External Stimuli And Intelligent Driving Behavior Of Flexible Montmorillonite-Based Membrane

Smart devices with the response to external stimuli like humidity,light,magnetism,electricity,thermal,etc.,can transform the stimuli into mechanical motion and show broad application prospects in many fields such as soft robotics,sensors,wearable devices,et al.But the development of the smart actuators faces some problems like high preparation-cost,low driving efficiency,poor mechanical stability,and the response to few stimuli,which greatly restricted their application.How to achieve the low cost actuators with fast actuation and complex deformation triggered by multi-stimuli remains the huge challenge,which depends on materials selection and structure construction of the smart devices.Montmorillonite(Mt),one type of natural layered clays,has many advantages such as abundance,environmentally friendliness,high specific surface area,good hydrated capability and large swelling capacity.So Mt becomes an attractive materials for the preparation of the actuators.To achieve control the fabrication cost and optimize the performance of the actuator,in this thesis,Mt as the main driving material is hybridized with graphene oxide(GO),reduced graphene oxide(r GO)and cellulose nanocrystalline(CNC),and then the membrane actuator is prepared by self-assembly.The controllability and complexity of the membrane deformation are improved by constructing arrays on the membrane surface.The response of the membrane to the multi-stimuli including the humidity,solvent and infrared light is studied.The main research contents are as follows:(1)Mt/OMt bilayer membrane with Mt as the humidity active layer and organic montmorillonite(OMt)as the inert layer is prepared by vacuum filtration method.The gradient distribution of OMt along the thickness of the membrane avoids poor interface adhesion and ensures the stable bending performance.When the relative humidity is94.26%,the bending angle of the bilayer membrane can reach 360°.The strip deflects upward to a curvature of more than 100° within 40 s upon exposure to the moisture and then recovers its flat shape within 20 s upon removal of the moisture source.After 200 times of repeated experiments,the bending curvature hardly changes,suggesting the superior bending stability of the bilayer membrane.In addition,the bilayer membrane shows good responsiveness to the organic solvent including ethanol,isopropanol and carbon tetrachloride.The membrane decorated with glue-based arrays shows more complex and controllable deformations,such as bending,twisting and coiling.Due to the good multi-response performance of RO/GM bilayer membrane,the as prepared soft actuators(window curtain,flower,gripper and tent)display reversible bending and predictable deformation.(2)RO/GM bilayer membrane with Mt and GO composites as humidity active layer and OMt and r GO composites as inert layer was prepared on grating plate by casting method.The as prepared membrane with the periodic grating pattern can respond to humidity,organic solvent and infrared light,bending toward RO side in response to the humidity and toward GM side under the stimuli of organic solvent and infrared light.The effects of r GO/OMt ratio on the membrane responsiveness in the moisture-inert layer were compared.It was found that with the increase of r GO/OMt ratio,the bending angle and bending rate of the bilayer membrane under the stimulus of humidity increase gradually,but the reversible-deformation capability of the bilayer membrane decreases.When r GO/OMT ratio exceeds 3/2,the membrane cannot return to the original shape state and has no shape-memory effect.Under the alternative stimuli of humidity/organic solvent or humidity/infrared light,the bilayer membranes exhibit reversible bidirectional bending.According to the multi-response performance of RO/GM bilayer membrane,they were successfully used for the preparation of soft actuator,such as a smart switch,a smart windmill,a bioinspired blooming flower,flapping-wing paper cranes and a curling tongue of animals.(3)The CNC-Mt(CM)rainbow membrane with cholesteric structures is prepared by the casting method.With the increase of Mt content,CM monolayer changs from blue to red,then to blue and finally milky white.CM bilayer membrane is prepared by casting hydrophobic α-cyanoacrylate with good hydrophilicity on the CM monolayer membrane.The bilayer membrane shows good response to humidity through the shape deformation and color change.Upon exposure to the high relative humidity,the membrane bends to the hydrophobic side and its color becomes shift red,while the membrane restores the original shape and color in low-humidity environment.With the increase of Mt content,the curvature of the bilayer membrane increases gradually,but the color of the membrane becomes lighter.The bilayer membrane with the Mt content of 3% has better comprehensive performance than other samples.Under the condition of gradient humidity,it shows obvious color change from bright green to red,and good actuation behavior,bending from 119° to 360° within 120 s and returning to its original shape within 27 s.Based on the shape deformation and unique color change of the membrane,it was successfully used for the preparation of soft actuator bionic butterfly,octopus and flowers are designed.