Research On The Application Of Thermal Management Composite Materials Based On Electrospun TPU Fiber Substrate In Flexible Wearable Device

In recent years,as electronic devices have become increasingly miniaturized and highly integrated,their operating frequency and the heat they generate have continued to increase,affecting the life and performance of electronic device,and even the safety of the entire system.Therefore,it is necessary to use high thermal conductivity materials for heat dissipation of electronic devices.At present,the main method to improve the thermal conductivity of materials is to add thermally conductive fillers such as boron nitride（BN）,aluminum nitride（Al N）,carbon nanotubes,and graphene（Gr）into polymer matrix.On the other hand,with the development of flexible wearable devices,the heat generated by the devices can damage human skin and cause injury,so low thermal conductivity insulation materials are needed to reduce the impact.Although traditional insulation materials can block some heat,excess heat can lead to further increase in the temperature of electronic devices,thus increasing the heat transferred to human skin.Phase change materials（PCMs）have a characteristic of high latent heat of phase change and can absorb a large amount of heat during the phase change process.The porous structure of electrospun fibers themselves provides insulation properties,and moreover,different performance nanomaterials can be loaded on electrospun fibers as substrates,which have a wide range of applications in various fields.Therefore,based on electrospinning technology,this paper prepares composite materials and structures with thermal management capability using electrospun fibers as substrates,which are applied to flexible wearable electronic devices,and carries out in-depth research on their mechanisms.First,we fabricated a flexible and breathable composite material with advanced thermal management capabilities.Boron nitride nanosheets（BNNSs）were used as a thermally conductive filler of random copolyester silicone（Ecoflex）were coated on the grids of patterned electrospun TPU fibrous mats.The composite exhibited a significant enhancement of thermal conductivity,and preserved the instinctive breathability simultaneously.When the composite was integrated into flexible devices,its saturating operating temperature dropped significantly compared to that with pure Ecoflex packaging.Moreover,the surface temperature fluctuation was less than 0.5℃during a more than 2000 cycles bending-releasing process.Finally,a prototype to fabricate wearable electronics with advanced thermal management capability was proposed.Our results provide a new route for the fabrication of next-generation of wearable devicesSecond,we fabricated a phase change composite material with excellent thermal insulation performance.Firstly,a high enthalpy binary eutectic phase change material based on myristic acid（MA）and stearic acid（SA）was prepared by optimizing the ratio,which had an enthalpy of 182.94 J g^-1.Then the MA-SA material was mixed into the Polydimethylsiloxane（PDMS）matrix,when the content of MA-SA was 40 wt%,the enthalpy of the MA-SA/PDMS composite material reached 70.48 J g^-1.After doping,the material was combined with electrospun TPU fibrous mats to prepare the MA-SA/PDMS/TPU thermal insulation material.Due to the high phase-change enthalpy of the phase-change material coupled with the porosity of the electrospun fibrous mats,this material has excellent thermal insulation properties.The surface temperature of the samples with the composite TPU fibrous mats all showed a decrease,when the composite was fixed on a heating table at 60°C,the 40 wt%MA-SA/PDMS/TPU composite with a TPU fibrous mats thickness of 0.60 mm delayed reaching the stable temperature by 170 s compared to that with pure PDMS,and the stable temperature decreased by approximately 10°C.In addition,the composites maintain excellent thermal insulation in the bending state.