Study on Electromagnetic Shielding and Acoustic Performance of Graphene-based Nanocomposites and Metastructures

Author:Li Ying

Supervisor:he xiao dong


Degree Year:2019





Graphene nanosheet exhibits attractional mechanical,electrical,optical and thermal properties,which endow it great potential as a nanofiller.It is introduced into polymer matrix by physical adsorption or chemical bonding,which improves the poor electrical conductivity and mechanical properties of the polymer,thereby obtaining multifunctional graphene-based composite materials and broadening the application fields of both graphene and polymers.However,it can’t meet a number of requirements concurrently only by improving properties of single materials.Therefore,how to combine the advantages of materials and structures to construct multifunctional materials is still a big challenge.In this paper,considering of designing multifunctional materials/structures,graphene-based nanocomposites and metastructures were designed and fabricated by introduction graphene into polymer,or constrcting acoustic metastructures.Moreover,the mechanical properties,electromagnetic interference shielding performance and acoustice properties of graphene-based nanocomposites and metastructures are characterized and anylsis to explore their potential application prospects.The main research contents are as follows:To improve traditional materials,the graphene sheets obtained by the liquid phase stripping method were introduced into styrene-butadiene rubber(SBR)latex,and graphene/SBR composites with different graphene content were synthesized by combining spray drying and hot pressing.The interface synergistic effect between graphene nanosheets and rubber matrix endows the nanocomposite with good mechanical properties.When graphene content is up 15 vol%,the Young’s modulus of the nanocomposites is enhanced by 30 times over rubber.Meanwhile,graphene layers can form conductive network in rubber matrix,which offers nanocomposites excellent electric and thermal conductivity.The electrical and thermal conductivity of nanocomposites with 15%volume fraction of graphene content are up to 219S/m and 2.922 W m-1 K-1 respectively,which is increased by 100 and 13 times compared to pure rubber.Also,nanocomposites can be served as good thermal interface materials.In addition,the electromagnetic shielding efficiency of graphene/SBR nanocomposites is exeed 45 dB in X band(8-12 GHz).Moreover,the nanocomposites exhibit excellent underwater sound absorption performance(average absorption coefficient exceeds 0.8 in the 6-30 kHz range).Notably,graphene/SBR nanocomposites still exhibit excellent water absorption performance with the increase of water pressure in the 0.1-5.5 kHz range.Hence,the multifunctional graphene/SBR nanocomposites have promising applications in electronics,thermal management and marine engineering.In order to solve noise problems in low frequency range,electromagnetic and acoustic double-shielding graphene-based metastructures were successfully designed and prepared by combing materials and metastructure advantages.Graphene papers were sythsized by freeze drying and hot-pressing methods,which exhibits good electrical conductivity(1580 S/cm)and mechanical properties(3.5GPa).For the first time,the acoustic properties and eigenmodes of graphene papers were investigated by nondestructive acoustic testing.We propose a novel metastructure based on graphene paper and artificial honeycomb,which exhibits not only excellent electromagnetic interference shielding property but also robust acoustic shielding efficiency.The EMI shielding effectiveness of metastructure is up to 74 dB in a broad range from 2.6 to 26.5 GHz.The acoustic shielding effectiveness reaches 25 dB from 200 to 1500 Hz.It is worth noting that the acoustic shielding effectiveness reaches up to 40 dB at very low frequency of 200Hz,breaking mass density law.A typical double-shielding application demo was assembled to further prove the attenuation performance of electromagnetic wave and sound.Our unique metastructure are very promising in protecting the electromagnetic and acoustic pollution.To achieve active control of acoustic frequencies,the graphene sheets were bonding together based on chemical adhesive of the amphoteric polyvinyl alcohol to form a composite film.Polyvinyl alcohol/graphene composite film with different graphene content were prepared by straightforward coated process.The addition of graphene effectively improves the mechanical properties and electrical and thermal conductivity of pure polyvinyl acohol films.When graphene content is up 24.3%,the Young’s modulus increased 1.5 times and electrical conductivity is 44.7 S/cm,which is over 100 times higher than that of insulation polyvinyl alcohol film.The first anti-resonant frequency of polyvinyl alcohol/graphene composite film can be actively tunable by external electric field,allowing for values of effective modulus of membrane to be adjusted,leading to excellent sound attenuation properties in severe environments.Additionlly,polyvinyl alcohol/graphene composite film can also be regard as multifunctional materials with good electromagnetic interference shielding performance.