Fabrication And Multi-stimuli-responsive Properties Of Polymer Film Via Co-extrusion Film Blowing Method

In recent years,inspired by the fact that natural organisms can change their shape or motion according to the changes in the external environment,soft actuators have attracted the wide attention of researchers.Soft actuators can convert external stimuli(such as light,electricity,humidity,magnetic field,organic solvent,etc.)into mechanical energy.It is controllable and versatile.They have been widely developed and applied in intelligent grasping,artificial muscles,soft robots and other intelligent equipment fields.However,the existing fabrication methods often suffer from complicated fabrication process,high cost,limited dimension and so on.Most of the prepared soft actuators are only respond to single stimulus,which greatly limits the production scale and application range of actuators.The scope of application cannot meet the needs of applications in complex and changeable environments.In addition,the existing actuators usually only have basic driving functions.The sensing signals generated in the driving process cannot be monitored and fed back in real time.This greatly limits the further development of soft actuators.Therefore,multiple response and multi-function have become the current development direction of soft actuators.In this paper,a multi-stimulus PVDF/LDPE bilayered actuator is simply and efficiently fabricated from thermoplastic polymer materials polyvinylidene fluoride(PVDF)and low-density polyethylene(LDPE)by polymer melt processing method.Furthermore,multiwall carbon nanotubes(MWCNTs)and single-walled carbon nanotubes(SWCNTs)are sprayed on the surface of the bilayered film PVDF layer as a carbon nanotubes(CNTs)conductive layer by a self-assembled roller-to-roll(R2R)spraying device.CNTs/PVDF/LDPE actuator with both driving and sensing functions is successively prepared.The main research and results are as follows:(1)PVDF/LDPE bilayered film with two thickness ratios(PL1 and PL2)are prepared by bilayered film blowing method.It is found that the film obtained by film blowing method has a certain degree of orientation in blowing up direction.The orientation of film determines the bending direction of the soft actuator.The actuator always bends perpendicular to orientation direction.By adjusting the angle between the long axis direction of the actuator and orientation direction,the shape change of the actuator can be programmed,such as coiling,left-and right-hand spiral,etc.In addition,PL1A(soft actuator based on PL1)exhibits good driving performance upon acetone vapor and is used as a worm-like self-walker.It can crawl on a dentate flat plane and an inclined plane under periodic stimulation.PL2A(soft actuator based on PL2)can exhibit good driving performance driven by temperature.Under the irradiation of periodic infrared lights,PL2 A can also be used as a crawler-type robot that could continuously roll and climb the steps,somewhat mimicking the tank track motion.It is found that PL2 A can be even actuated by human body temperature.It can be used as a smart gripper for transporting goods.The above results show that the prepared PVDF/LDPE bilayered films have great application potential in soft robots and artificial muscles.(2)On basis of the PVDF/LDPE bilayered film prepared by bilayered film blowing method,MWCNTs and SWCNTs are sprayed repeatedly on the surface of PVDF layer.CNTs/PVDF/LDPE composite film with good conductivity are successfully prepared by R2 R spraying cycles.The combination of MWCNTs and SWCNTs helps to improve the conductivity and adhesion of the films.The surface resistance of the film decreases rapidly and then slowly with the increase of spraying times.The conductive layer presents a typical I-V characteristic curve.The adhesion between CNTs conductive layer and the film surface is systematically tested.It is found that the surface resistance of the film does not change significantly under strong scrape,indicating that the bonding between the conductive layer and the film is good.Finally,the piezoelectric voltage output signal generated by the actuator based on the CNTs/PVDF/LDPE composite film was tested.It is found that the higher the concentration of acetone vapor is,the higher the piezoelectric output signal of the actuator is.The higher the temperature is,the higher the piezoelectric output signal of the actuator is.The sensor signal generated by the actuator during driving process can be monitored and fed back.The above research content provides a new strategy for fabricating actuators with sensing functions.