The Preparation And Hygroscopic Response Behavior Of PVA-co-PE Nanofiber-Based Soft Actuator

Smart materials are emerging materials that combine self-sensing and self-actuating characteristics,which embodies of intelligent imitation of biological behavior.The traditional nanofibers are also developing towards the direction of intelligent bionic motion through functionalization.As an important part of smart devices,the soft actuator can transform the energy in the environmen into the kinetic energy that can be directly used by people,realizing the efficient use of energy.In previous studies of soft actuators,the light,heat and electricity were often used as stimulus sources,but they are generally faced with many problems such as complex processes and high costs.However,water or moisture stimulus response actuators are gradually enriching and expanding the scope of smart devices due to their wide range of stimulus sources and environmental friendly characteristics.Ggraphene oxide(GO)is considered as an ideal candidate for humidity-responsive actuators due to its excellent humidity sensitivity.In order to improve the hygroscopic response of the material,three kinds of moisture-responsive soft composite membrane,which were called PVA-co-PE/GO composite membrane 、 AgNWs/PVA-co-PE/GO composite membrane and AgNWs-PVA-co-PE/GO conductive bilayer membrane,were prepared by evenly dispersing GO sheets and silver nanowires(AgNWs)into three-dimensional network formed by PVA-co-PE nanofibers.They can be used as the humidity-responsive device to produce rapid and reversible large-scale bending and deformation behavior,and realize energy transformation on the nanoscale.The research contents and experimental results are as follows:(1)The PVA-co-PE/GO composite membrane was prepared by spraying method of mixed solution with GO solution and PVA-co-PE nanofiber suspension.The actuating mechanism of PVA-co-PE/GO composite membrane and the effects of different GO content and humidity conditions on the actuating performance were mainly studied.The result showed that when the membrane was exposed to moisture stimulus,GO in the high-humidity side quickly absorbed water and caused volume expansion.The asymmetric structural caused the membrane to bend to the low-humidity side.According to the driving performance,the optimal content of GO was determined to be 9 wt%,and the maximum bending angle of the composite membrane increased with the increase of water temperature and thedecrease of environmental humidity.(2)The AgNWs/PVA-co-PE/GO composite membrane was prepared by spraying method of mixed solution with the PVA-co-PE nanofiber suspension,AgNWs alcohol solution and GO solution.Compared with the PVA-co-PE/GO composite membrane,the added AgNWs was randomly scattered among the GO sheet layers,making the structure of the membrane more loose and porous,which was more conducive to the rapid water molecule adsorption-desorption process,thus thus reducing the response time by 60% and the recovery time by 70%.The maximum bending angle of 145° in 1.2s was achieved under the optimal humidity stimulation condition,and the good driving performance was still maintained after100 reversible bending recovery cycle tests.The membrane can be made into smart devices such as smart tweezers and bionic crawlers under the micro-stimulation of the palm or fingertip.(3)The AgNWs-PVA-co-PE/GO conductive bilayer membrane was prepared by the way that the mixed solution with GO solution and the PVA-co-PE nanofiber suspension was sprayed on the substrate and then the AgNWs were separately layered sprayed on the PVA-co-PE/GO layer.Compared with the PVA-co-PE/GO composite membrane,the AgNWs on the surface formed a conductive path,which gives the AgNWs-PVA-co-PE/GO bilayer membrane excellent conductivity.The experimental result showed that when the content of AgNWs was 10 wt%,the bilayer membrane surface resistance is 2.68 Ω and can remain stable under arbitrary bending state.But,the cumulation of AgNWs increases the bending strength of composite membrane,which has slightly negative influence on actuating performance.The conductive bilayer membrane was connected to the control circuit and used as a smart switch,which successfully realized the light bulb on-off action.