Preparation Of Fe₃O₄/EVA Bidirectional Shape Memory Composite Film And Light-thermal Response Research

The shape memory polymer can be restored to its original shape from a predetermined temporary shape under the stimulation of the external environment（such as heat,light,electricity,magnetic field or solution,etc.）.It is a typical smart material and can be deployed in the space and the smart sensor,biomedical self-healing system and other important application value.The traditional heat-induced shape memory polymer has a single response stimulu and can only achieve irreversible unidirectional shape memory recovery,which severely limits the application of shape memory polymers.By adding functional fillers to the shape memory polymer,not only can it increase its stimulus,but also improve its response performance,mechanical properties,etc.So the particle-filled shape memory polymer has become a research hotspot in recent years.In this paper,the semi-crystalline polymer ethylene-vinyl acetate co-polymer（EVA）was used as the shape memory matrix,and the Fe₃O₄ nanoparticles were used as the light-thermal response filled particles to study the micro-structure,shape memory properties,and the light-thermal response;COMSOL was uesd to simulate the temperature field of the composite film with different arrangements of particles under light,heat and light-thermal coupling.First,carbon-coated Fe₃O₄ nanoparticles（C@Fe₃O₄ nanoparticles）were synthesized by Solvothermal,and PVP-coated Fe₃O₄ nanoparticles（PVP@Fe₃O₄ nanoparticles）were prepared by surface modification with PVP.By changing the content of oxidant H₂O₂,the effect of oxidant on the size and magnetic properties of C@Fe₃O₄ nanoparticles was discussed.The results showed that the particle size and grain size of C@Fe₃O₄ nanoparticles increased with the increase of the amount of added H₂O₂.PVP@Fe₃O₄ nanoparticles had better magnetic properties than C@Fe₃O₄nanoparticles;the photonic crystal colloid solutions of C@Fe₃O₄ and PVP@Fe₃O₄ nanoparticles were magnetically responsive,and the structural color depended on the size of the particles and the strength of the magnetic field.Using PVP@Fe₃O₄ nanoparticles with excellent magnetic response as filled particles,Fe₃O₄/EVA composite film was prepared by solution blending method.The results showed that the addition of Fe₃O₄ nanoparticles had little effect on the melting temperature of the material.The light-thermal effect test results showed that Fe₃O₄ nanoparticles had a strong light-thermal effect,and the temperature of the composite film could be controlled by adjusting the content of Fe₃O₄,the intensity of light,and the thickness of the film;another experiment showed the addition of Fe₃O₄ nanoparticles gave the composite film magnetic response performance and under thermal stimulation,it could improve the shape recovery rate and reduce the shape fixation rate of the film;under the effect of infrared laser,the composite film had excellent light-thermal response performance;the prepared 1.5 wt%Fe₃O₄/EVA composite film can achieve bidirectional shape memory and had good reversible circulation;the anisotropy of the optical properties of the composite film prepared under the induction of magnetic field was characterized by the optical microscope.In order to solve the problem of uneven heating of the composite film in the thickness direction,this topic used COMSOL to simulate the temperature field of a composite film with uniform particles,decreasing top-down,and increasing top-down distribution under the action of light,thermal,and light-thermal coupling,and analyzed the effect of three arrangements on the thermal transfer of the material.According to the simulation results,the best uniform heating condition of the composite film is:the magnetic nanoparticles are controlled to increase in the thickness direction from top to bottom,and the source of stimulation is light.In summary,compared with pure EVA film,Fe₃O₄/EVA composite film has a magnetic response,and can be controlled by infrared laser and thermal field stimulation to achieve shape memory performance,which solves the problem of traditional shape memory polymers,responding to a single stimulus.Under the stimulation of light and heat,bidirectional shape memory can be realized,which solves the problem that the conventional shape memory polymer can only deform in one direction.This has attractive application prospects and important research significance in the fields of dynamic electrical conduction,intelligent light-thermal regulation and controllable fluid transmission.