Design Of Structure And Interface Of Three-dimensional Graphene And Application In Thermal Management

With the miniaturization and integration of electronic components,the power density increases rapidly,and the heat generated by electronic devices also increases.To ensure that electronic components work in an appropriate environment,heat must be dissipated effectively.Otherwise,high temperature will reduce the efficiency and life of the device.The effective implementation of thermal management strategy can alleviate this problem.The overall heat dissipation design of the system not only needs to optimize the electronic packaging structure,but also depends on the development of high-performance thermal management materials.Graphene,exhibits excellent in-plane thermal conductivity of 3,500–5,300 W m^-1 K^-1,and is often added to polymer matrix or directly prepared as pure graphene thermal management materials.However,graphene is an anisotropic two-dimensional nanomaterial with through-plane thermal conductivity three orders of magnitude lower than excellent in-plane heat transport.The random disordered dispersion of graphene and phonon scattering between various surfaces will affect the improvement of thermal conductivity.Therefore,in order to maximize its in-plane heat transfer effect,it is necessary to regulate the structure of graphene to form a uniform and orderly arrangement,and to enhance the interface transport of phonons by optimizing the interface design.In view of this,this paper focused on the microstructure regulation and interface design of graphene and prepared three kinds of high-performance graphene-based thermal management materials.The research contents include the following three parts:（1）Preparation and properties of graphene-based heat spreader with high thermal conductivity and electromagnetic shielding effectiveness based on enhanced interface with MXeneIn view of the difficulty of constructing three-dimensional continuous thermal and electrical conduction network in polyolefin,an origami fabrication strategy was proposed to prepare polyethylene（PE）composites by incorporation of well-aligned MXene nanosheets premodified graphene woven fabrics into the matrix.Firstly,the GWFs prepared by chemical vapor deposition（CVD）technology were treated with oxygen plasma,and Ti₃C₂T_x MXene nanosheets were sprayed.Then it was transferred to PE film and folded by origami process.Finally,the composites were obtained by hot pressing.The seamless graphene framework prepared by CVD overcomes the drawbacks of conventional filler networks assembled by graphene nanosheets,which have high interfacial resistance between adjoining nanosheets.And,the interface between MXene and graphene is strengthened by the formation of hydrogen bonds using the proposed approach,instead of weak van der Waals interactions.Therefore,composites exhibit excellent thermal conductivity of 9.26 W m^-1 K^-1 and high electromagnetic interference shielding effectiveness（EMI SE）of 61.0 d B.In this paper,it is proved that the optimal design of the interface between nanofillers is an effective strategy to promote the physical properties of the composites at the same filler loading.In addition,this method shows versatility and can be used to improve the properties of other thermoplastic polymers.（2）Preparation and properties of high performance vertically aligned graphene thermal interface materials based on surface modification of gold nanolayersIn view of the demand of high through-plane thermal conductivity and low contact thermal resistance for high-performance TIMs,a simple and effective method was proposed to prepare gold-nanocap-modified vertically aligned graphene monolith（Au/VAGM/Au）.Specifically,porous polyurethane（PU）thin films were adhered to the graphene papers,cut into strips and rolled into disks by hand.After polishing,a layer of nano-thick Au foil was transferred to the upper and lower surfaces for modification.Vertically aligned graphene provides an efficient heat transport path to meet the demand for high through-plane thermal conductivity of TIMs(276 W m^-1 K^-1),Porous PU foams provide compression space to meet the compressibility requirements of TIMs（At 30%strain,the compressive stress of VAGM is 0.36 MPa）,and Au foils can further reduce contact thermal resistance(Au/VAGM/Au:0.41 K cm² W^-1).our proposed graphene-based TIMs exhibits an enhancement in cooling efficiency of≈1.15 times compared to that of the state-of-the-art TIMs(EX10000F7,30 W m^-1 K^-1)in the TIMs performance test,manifesting its superior ability to meet the ever-increasing heat dissipation requirement.（3）Preparation and properties of ultrathin solid thermal interface materials based on crumpled grapheneIn view of the disadvantages of“dry-out”and“pump-out”of thermal grease during prolonged periods of operation,as well as the problem of thick bond line thickness of thermal pad,ultrathin solid graphene TIMs with thermal grease-level thermal interface resistance was developed.Firstly,graphene was grown on the surface of the nickel mesh using CVD technology.When the nickel was removed by marble etching solution,the unprecipitated carbon dissolved in the nickel matrix during CVD rearranged along the interface of nickel/etching solution to obtain amorphous carbon/graphene woven fabrics（AC/GWFs）.After heat treatment at 500°C,the AC decomposed and the originally horizontally graphene crumpled and turned into a vertical alignment-like structure that looks like tremella（CGWFs）.The thermal interface resistance of CGWFs as low as 0.083 K cm² W^-1 at 100 psi,and the thickness of tested CGWFs decreases from≈400μm to 12μm after testing,with the shape variation of 97%.In addition,CGWFs is composed of pure inorganic graphene and can be used in the wide temperature range of liquid nitrogen（-196°C）to 500°C.Compared to the silica-based TIMs with limited application range（-50°C-200°C）,it shows great potential in thermal management applications in deep low temperature such as infrared focal plane detector and high temperature such as thermoelectric generators.