Preparation Of Sandwich-type Carbon-based Composite Phase Change Materials And Its Electromagnetic Shielding Performance

With the rapid development of 5G technology,the rapid development of modern electronic and telecommunication equipment,advanced electronic equipment towards miniaturization,integration direction continues to develop,the power density of electronic equipment is increasing at the same time also lead to its high-speed operation in a limited area when a large number of heat and electromagnetic waves.Heat accumulation and electromagnetic radiation will not only reduce the efficiency and reliability of electronic equipment,and reduce the life of electronic equipment,so it is necessary to make electromagnetic shielding materials with efficient heat dissipation performance and efficient electromagnetic shielding performance.However,the current electromagnetic shielding composites usually have only a single shielding performance,which cannot meet the demand of multiple functions in the application environment.The structure and properties of multilayer structural composites are well designable,providing a simple and feasible way to achieve an effective combination of thermal conductivity and electromagnetic shielding performance.The multifunctional electromagnetic shielding materials with thermal management properties and electromagnetic shielding properties with absorption-driven are suitable for applications such as high-frequency communication and integrated modular devices.Therefore,the study of thermally conductive functionalized electromagnetic shielding materials will greatly promote their application in electronics with great application potential.In this thesis,a carbon-based phase change composite material was prepared by using expanded graphite as composite skeleton and substrate,carbon nanotubes as thermally conductive and electrical additives,and phase change material n-eicosane as thermal management material,combined with melt blending,ultrasonic assisted,vacuum drying and adsorption,and cold pressing molding techniques.The effects of doping parameters on electrical conductivity,electromagnetic shielding properties,and thermal conductivity were systematically investigated.Magnetic nanoparticles were introduced to enhance the absorption of electromagnetic waves in the composite,and in order to enhance the effective concentration of magnetic nanoparticles,magnetic nanoparticles were loaded into electrospun films by electrostatic spinning technique and uniformly distributed in their internal network structure,which exhibited electromagnetic shielding properties not possessed by pure polymer films by using the magnetic loss effect of magnetic nanoparticles on electromagnetic waves.The carbon based phase change composites were laminated with the magnetic spinning films to form sandwich type phase change composites,and the influence of the sandwich structure and the internal three-dimensional network structure of the phase change composites on the electromagnetic shielding was thoroughly investigated,the thermal management properties possessed by the sandwich type composites were studied,and the absorption-dominated electromagnetic shielding mechanism was analyzed.The prepared carbon-based phase change composite has an electromagnetic shielding effectiveness of 67.4 d B and an average absorption rate of 79.76%.Its electromagnetic shielding performance shows a response to temperature,and when the temperature reaches its phase change temperature,the conductivity increases from 132.2S/cm to 146.2/cm,the total electromagnetic shielding effectiveness increases to 78 d B,and the average absorption rate increases to 80.6%,showing a better electromagnetic shielding performance.At the same time,the composite material has excellent thermal conductivity of 4.93W/mk.The sandwich type phase change composite material,which combines magnetic spinning film and phase change composite material,exhibits excellent electromagnetic shielding performance of 98.4d B and average absorption rate of 84.7%.After reaching above the phase change temperature,the total EMI shielding performance of the composites increased to 115.75 d B and the average absorption rate reached 85.2%,showing the temperature tunable EMI shielding performance.In addition,the obtained composites have excellent thermal conductivity(3.61 W/mk)and show effective heat dissipation in electronic devices.In conclusion,sandwich-type phase change composites have great potential for applications in the field of thermal management and electromagnetic shielding of electronic devices.