Research On Flexible Actuation Performance Of Temperature-responsive Low-density Polyethylene Composite Film

Soft actuators based on stimulus-responsive materials can generate the corresponding deformation by the stimulation of external.They can be used in artificial muscles,robots,drug transportation,and so on.Robots based on these soft actuators can be made small enough to meet specific needs and has a wide application prospect.However,limited by size the existing small-scale soft robots(size less than1 cm)usually have a simple structure and can only achieve simple functions or move.And these small-scale robots rely on external control and energy supply to move and work.How to make a small-scale robot with multiple functions and modes of motion and can obtain energy from the environment for autonomous motion is still a challenge.To solve these problems,based on the principle of deformation caused by asymmetric thermal expansion of multilayer composite films,low-density polyethylene films with a large coefficient of thermal expansion were compounded with other materials.A series of temperature response thin-film actuators are fabricated,respectively.And the working and motion modes of the actuators under different heating conditions are studied.The research contents are as follows:1.Transparency is an effective way to achieve camouflage,which is widely used by various creatures in nature.However,the traditional photothermal temperature response actuators are in contradiction with the required light transmission characteristic of the transparent actuator due to its necessary light absorption characteristics.Here,by the excellent light-to-heat conversion efficiency and light transmission characteristics of the multi-walled carbon nanotube(MWCNTs)film,a transparent photothermal temperature response bimorph film actuator was fabricated by MWCNTs with extremely low thermal expansion coefficient and low-density polyethylene(LDPE)with extremely high thermal expansion coefficient.Because of the great difference in the thermal expansion coefficient of the two materials,even if the actuators absorb only a few lights and the temperature increases less,the actuators can be driven to generate reversible deformation.The actuators have dual characteristics of photothermal driving and light transmission,and the actuators with different bending directions can be obtained by adjusting the angle between the orientations of the two materials.In addition,the actuator is also a kind of actuator with multiple responses,which can be driven not only by photothermal but also electrothermal.2.Limited by the size of small-scale robots,they are usually simple in structure and unable to achieve various motions to adapt to changing environments with one control method.The emergence of multi-motion transformable actuators with only one stimulus provides a solution to this problem.Here,photothermal bimorph actuators generating deformation based on the asymmetric thermal expansion of the bilayer structure combine with a shape-memory material having thermal shrinkage property LDPE for the first time.The resulting new photothermal actuators can be transformed simply by heating or illumination so that they obtain different shapes and functions.Further,an actuator is made into a light-driven transformable small-scale robot with multiple motion abilities,including crawling,rolling,and oscillation.Simply driven by light,the robot can transform from a crawling robot capable of moving at the speed of 2.28 mm s^-1 to a rolling robot moving at the speed of 6.9 mm s^-1.With further transform,the robot can autonomously oscillate at the frequency of 3Hz under the irradiation of the directional beam.The results demonstrate a way of realizing multiple functions and motions on one actuator and small-scale robot with one method control.3.Also limited by the size of small-scale robots,they are also difficult to integrate energy supply and control functions on themselves.They can only work independently by supplying energy from the outside or obtaining energy from the environment and cannot work independently from outside control.This also limits the application of small-scale robots.Here,the temperature response thin-film actuators are heated by directly heating one side of the actuators in the way of heat conduction.Under the combined effect of heat conduction and heat convection of air,the temperature of the thin-film actuators will oscillate autonomously without control.The phenomenon of temperature fluctuation is used to realize the independent oscillation motion of thin-film actuators with different structures without external control.Further,a small-scale robot that can crawl independently in a stable environment without external control is made.The robot can continue to crawl autonomously on the hot surface until it leaves the surface.