Preparation and Properties of Three-dimensional Graphene Network Structure Composites

Author:Xu Fan

Supervisor:li yi bin peng qing yu


Degree Year:2019





Graphene as a two-dimensional nano material,has excellent mechanical,electrical,thermal and optical properties,and it is known as the"The king of new materials".However,the nanometer size of graphene limits its application.The assembly of graphene into macroscopic bodies is one of the breakthroughs in the application of graphene.In recent years,with one-dimensional fiber,two-dimensional film,the three-dimensional network structure of graphene macro body has a number of innovative achievements,especially,the three-dimensional graphene network has more widespread attention.But adjusting the flexible and density of three-dimensional network structure is a bottleneck problem,and in acoustic performance research is still blank.In this article,based on three-dimensional graphene network.In order to improve the mechanical properties and extend the multifunctional applications of graphene composites,three-dimensional flexible and sound absorption integration structure,graphene network/PDMS composites and variable density graphene network structure are prepared.The properties of these composites were characterized.The graphene aerogel was prepared by freeze-drying.A three-dimensional network structure with graphene was constructed successfully.Through the chemical characterization,graphene has fewer defects and well crystal structure.The mechanical properties of three-dimensional graphene network structure was tested,the compression strength was only 0.002 MPa,when the strain was 17%.In order to improve the mechanical properties of graphene aerogel,the flexible honeycomb structure was introduced into the graphene network system.Excitingly,the compression strength is 1000 times compared to graphene aerogels,and show well fatigue resistance performance.After 1000 cycles of compression,the strength remained 90%.In addition,standing wave tube method was used to test the sound absorption performance of the three-dimensional graphene network integrated material.The pure graphene three-dimensional network structure has frequency selection characteristics,while the acoustic characteristics changed greatly after the honeycomb structure was introduced.The synergistic effect between honeycomb structure and graphene network improve the sound absorption performance of composite.In 9004000 Hz frequency range,the absorption coefficient is more than0.8.Addtionally,in the range of 12001500 Hz,the absorption coefficient reach to0.97.Based on the three-dimensional graphene network structure,through tune the porosity and thermal treatment,the conductivity of three-dimensional conductive network had been improved 1000 times,reach to 100 S/m.The flexible polydimethylsiloxane(PDMS)matrix is directly infiltrated into graphene network using vacuum technique.It not only solved the problem of easy agglomeration of graphene,but also obtains composites with high electrical conductivity.Additionally,the three-dimensional graphene networks also improved the mechanical properties of composites,tensile strength was increased by 63%and young’s modulus increased by 11 times.Through the microscopic characterization and electrical properties test,the result showed that graphene had good dispersion in the composites.The conductivity of the three-dimensional graphene network was kept well,and endowed the composites have electromagnetic shielding.When the thickness of composites was 2 mm,in the frequency of 8-12 GHz,the electromagnetic shielding efficiency reached 54 dB.The electromagnetic wave was shielded more than 99.999%.The electromagnetic shielding mechanism of the composite was analyzed and described.Part of the electromagnetic waves were reflected due to the highly conductive graphene connectivity network,and the electromagnetic wave entering the composite material was absorbed by graphene because of dielectric relaxation effect,thus the composites have high electromagnetic shielding.Through the high temperature graphitization process,the mechanical property of three-dimensional graphene network structure was transformed from elasticity to flexibility.The vacuum pressing technology was adopted to adjust the porosity of graphene network in a wide range to produce variable density graphene network structure.With the porosity increasing,the comprehensive performance of graphene paper was improved greatly.When the density reached 1.85 g/cm3,the tensile strength was increased to 50.4 MPa,and the toughness is 0.93 MJ/cm3.Moreover,the graphene paper changed from brittle to foldable,the tear resistance reached 1N/mm,showed isotropic,and the conductivity reached 1.1×105 S/m.In addition,the thermal conductivity reached 1100 W m-11 K-1,when the thickness is 80μm,in the frequency of 2-40 GHz,and the electromagnetic shielding efficiency reached 77.2dB.