Preparation Of Flexible Thermal Management Materials Based On Ultrasonic Forced Infiltration

At present,electronic products are rapidly developing towards miniaturization and multi-function.The heat generated during the operation of equipment seriously affects the performance and service life of electronic equipment.Therefore,it is urgent to develop thermal management materials(TMMs)with excellent thermal conductivity to reduce the heat accumulation of electronic devices.The thermal conductive polymer composites have been widely used in the field of TMMs due to their comprehensive properties of light weight,corrosion resisting,easy processing,low-cost,and good flexibility.However,the low λ of polymer matrix seriously limits the wide application of polymer materials in TMMs field.Hence,adding fillers with high λ is an effective and common solution to improve the λ of polymer composites.In general,polymer and thermal conductive filler are blended to construct thermal conductive network,but this method is easy to cause serious phase separation phenomenon.The thermal conductive network formed by blending method is generally self-assembled network,and the orientation degree is poor.Although vacuum filtration,lamination and other methods can build a continuous and dense thermal conductivity network,the traditional negative pressure infiltration process cannot meet the requirements of high viscosity matrix for efficient infiltration of dense thermal conductivity network.Therefore,we propose ultrasonic forced infiltration(UFI)method.The method firstly constructs a dense thermal conductive network by vacuum filtration,and then use high-frequency and high-power ultrasonic vibration to infiltrate the polymer matrix(thermosetting or thermoplastic polymer)into the network.Thus,high thermal conductivity polymer composites are obtained.The effects of ultrasonic time,frequency and amplitude on the properties of the products are systematically studied.By selecting different thermal conductive fillers and polymer matrix,thermal conductive polymer materials with specific functions are prepared.At the same time,the performance of composite is further verified in thermal management application.The specific research contents include:(1)The effects of ultrasonic frequency,ultrasonic time and ultrasonic amplitude on the comprehensive properties of thermal conductive polymer composite products prepared by UFI method are studied.The selection of polymer has great influence on the setting of ultrasonic time:viscosity affects the selection of ultrasonic time.When the polymer with low viscosity is used as the matrix,the ultrasonic processing time only needs 2～3 s.When the polymer with high viscosity is used as matrix,ultrasonic treatment is needed for ～10 s.The best experimental conditions for the preparation of thermal conductive polymer composites by this method are the amplitude between 50% and 60%.(2)CNT-Gr/PDMS composites are prepared by UFI method using carbon nanotubes(CNT)and graphene(Gr)as thermal conductivity fillers and polydimethylsiloxane(PDMS)as matrix.When the ratio of CNT to Gr is 3:1,the CNT-GR(3:1)/PDMS composite has a high λ(4.641 W/(m·K)),which is 1619% higher than that of the pure PDMS matrix.At the same time,the product has good electrical conductivity(447 S/m),electromagnetic shielding performance and excellent mechanical properties.(3)BNNS-CNC/PDMS composites are prepared by UFI method using BNNS nanosheets(BNNS)and nanocellulose(CNC)with excellent electrical insulation performance as fillers and PDMS as matrix.When the BNNS/CNC ratio is 25:1,the λ of BNNS-CNC(25:1)/PDMS composite is 7.309 W/(m?K),2607% higher than pure PDMS matrix.In addition,the products also have excellent dielectric properties,electrical insulation properties and mechanical flexibility.They can be used as TMMS and have strong application potential in the heat dissipation of electronic equipment.(4)In addition to the thermosetting matrix,thermoplastic butylene terephthalate(PBAT)matrix is selected to verify the applicability of the UFI method.CNT-CNC/PBAT thermal conductivity composites are prepared by UFI.When the mass ratio of CNT to CNC is 10:1,the λ of CNT-CNC(10:1)/PBAT composite material is 4.082 W/(m ? K).In addition,CNT-CNC(10:1)/PBAT composites have good mechanical properties,electrical conductivity,thermal stability and electromagnetic shielding performance.