Study On Preparation Of Transparent Flexible PU/ILs Composite Materials And Its Microwave Absorbing Performance

In recent years,with the increasing application of microwave absorbing materials in various fields,developing microwave absorbing materials with corresponding properties based on actual application scenarios has attracted more attentions.Transparent and flexible microwave absorbing materials can be integrated with other objects and devices imperceptibly,and can be used for electromagnetic stealth technology in special parts of aircrafts such as solar panels,cockpit windows,and complex optical equipments.In addition,transparent and flexible microwave absorbing materials can also be applied in fields such as display of medical imaging devices,wearable electronic devices,and microwave darkroom windows.Therefore,transparent and flexible microwave absorbing material is of great importance for practical applications.Owing to their high electrical conductivity,high dielectric constant,and high light transmittance,ionic liquids(ILs)have become a new type of green microwave absorbing materials with great potential.However,ILs are mainly used as modifier with a small amount of doping when used to design microwave absorbing structures,and they have several disadvantages such as easy to absorb water and easy to leak.To avoid the above-mentioned disadvantages,in this thesis,ILs were loaded into polyurethane(PU),which is a flexible polymer elastomer material with good optical transparency and mechanical properties,to prepare transparent flexible PU/ILs composite materials,and the physical properties and microwave absorbing properties of PU/ILs composite materials were studied.In this thesis,a new preparation method of PU/ILs composite materials based on prepolymer method was proposed,in which ionic liquids were used as the main microwave absorbing component.A variety of PU/ILs composite materials with different types([EMIm][N(CN)2]、[EMIm][BF4]、[EMIm][NTf2])and different mass fraction(0-30%)of ILs were prepared.The successful loading of ILs in PU was verified by infrared spectroscopy,X-ray diffraction and scanning electron microscopy.To obtain the impact of different types and contents of ILs,the thermal stability,tensile properties,light transmittance and electrical conductivity of PU/ILs composite materials were characterized and compared with pure polyurethane.This method has low cost and simple preparation process,providing a new idea for designing transparent flexible absorbing materials.The prepared PU/ILs composite materials have good thermal stability,tensile properties,light transmittance and conductivity.The dielectric constant and microwave absorbing properties of PU/ILs composite materials were studied by using rectangular waveguide/coaxial line method,and the microwave absorbing properties of PU/ILs composite materials with different types and contents of ILs were compared from the perspective of conductivity.The effects of different types and contents of ILs on the microwave absorbing properties of PU/ILs composites were obtained.Electromagnetic parameters obtained from testing were used in electromagnetic simulation software to establish a rectangular waveguide model,which verified the accuracy of the experimental results.Finally,the microwave absorbing properties of PU/ILs composite materials with different thickness were obtained by simulation,which laid a foundation for the design of microwave absorbing structure based on PU/ILs composite materials.In summary,in this thesis,we combined ILs with excellent microwave absorbing characteristics and PU to prepare transparent flexible PU/ILs composite materials,which achieved good electromagnetic wave absorption in X-band.Our work further expanded the application of ILs in microwave absorbing field,providing new ideas for designing transparent and flexible microwave absorbers.