Preparation And Performance Of Thermally Conductive And Superhydrophobic Polyurethane Composites

Thermally conductive polymer-based composites,as the main materials to solve the thermal management issues caused by the development of modern electronic products that tend to be highly integrated,lightweight and flexible,and functionally diversified,have important research value and application potential,and have received continuous attention from researchers at home and abroad in recent years.However,the reported methods for preparation of thermally conductive polymer-based composites generally have problems such as harsh experimental conditions,complicated operational processes and high preparation costs.On the other hand,the thermal management capability of thermally conductive polymer-based composites can be severely affected due to surface contamination by dust,rain,snow,and other solid particles,liquids,etc.in a complex and diverse external environment.Therefore,imparting thermally conductive polymer-based composites with superhydrophobicity assists to eliminate adverse factors in the external environment that may have an impact on their thermal management capabilities.This provides new opportunities to expand the application scenarios and fields of thermally conductive polymer-based composites.In this paper,thermally conductive and superhydrophobic composites were constructed by using boron nitride material as a thermally conductive filler,which were compounded with polymer matrix through structural design innovation.The microstructure of thermally conductive filler inside the material,the formation principle of the thermally conductive pathway and the heat conduction mechanism were investigated.Furthermore,the synergistic effect between superhydrophobicity and thermal management capability was investigated.The specific research contents and results are concluded as follows:(1)Preparation,microstructure control,thermally conductive mechanism and properties research of thermally conductive boron nitride nanosheets/thermoplastic polyurethane electrospun composite membrane.The microstructure of thermally conductive filler inside the polymer was designed based on the thermally conductive theory.The highly oriented arrangement structure of boron nitride nanosheets(BNNSs)inside the thermoplastic polyurethane(TPU)fibers membrane was constructed by electrostatic spinning process in which the mixed solution of BNNSs and TPU was strongly stretched and extruded in a high voltage electric field.Afterward,the BNNSs thermally conductive network was formed with the interconnected network-like structure of electro spun fibers to produce TPU/BNNSs thermally conductive composite membrane material.The effects of spinning voltage,spinning solvent ratio,spinning propulsion rate and addition of BNNSs on the microscopic morphology and thermal conductivity of the composites were explored;the stability of thermal conductivity of the composites after 500 stretching and bending experiments was investigated;the thermal stability and mechanical property of the composites were examined.Results show that the thermal conductivity of the prepared TPU/BNNSs thermally conductive composite membrane material is 6.28 W/m·K at 40 wt%of BNNSs content,and its thermal conductivity are 6.08 W/m·K and 6.05 W/m·K even after 500 times of stretching or bending,corresponding to only 3.2%and 3.7%of depreciation and showing good stability of thermal conductivity.The thermal stability and mechanical property of the composite were also improved.In the application study as a thermal management materials,TPU/BNNSs thermally conductive composite membrane material could achieve a cooling performance of 8.76℃.(2)Preparation of thermally conductive TPU/BNNSs composite membrane by ultrasound-assisted and their stable thermally conductive pathway construction mechanism and thermally conductive performance research.In order to solve the potential problem that thermally conductive pathway constructed by thermally conductive filler was blocked by the polymer matrix,BNNSs were assembled on the surface of TPU electrospun fibers through an ultrasonic-assisted assembly process that taking advantage of the strong impact force of ultrasonic wave and cavitation effect of the ultrasonic field.Afterward,a three-dimensional BNNSs thermally conductive network structure was fabricated by combining the cross-through fiber network inside the electrospun membrane to improve the thermal management capability of TPU polymer matrix.The effects of filler dispersion reagents,ultrasonic temperature,ultrasonic time and ultrasonic power on the microscopic morphology and thermal conductivity of the fabricated TPU/BNNSs thermally conductive composite membrane materials were investigated.The thermal conductivity after 500 times of stretching and bending experiments,and thermal stability of the obtained composite material were also examined.Results show that the thermal conductivity of TPU/BNNSs thermally conductive composite membrane material reaches 6.93 W/m·K when deionized water is the dispersing reagent,the sonication temperature is 30℃,the sonication time is 1 h,and the sonication power is set as 250 W.The thermal conductivity are 6.68 W/m·K and 6.64 W/m·K after the stretching and bending experiments,respectively,corresponding to the depreciation rate are only 3.5%and 4.1%.The thermal conductivity and its stability of the material are very positive.When the prepared composite was applied as a thermal management material,a cooling performance of 8.94℃ can be achieved.Thermally conductive polymer-based composites with good thermal management capability can be produced by an efficient and environmentally friendly ultrasonic-assisted assembly method.(3)Preparation of thermally conductive and superhydrophobic composite membrane and researches of the synergistic performance mechanism of thermally conductive and superhydrophobic effect,and thermal management stability.In order to solve the issue of thermal management capacity loss of thermally conductive polymer-based composites due to contamination by dust,rain and snow as well as various types of solid particle and liquid substance when applied in external environment.Superhydrophobicity was achieved by spraying hydrophobic SiO2 particles with PDMS mixture solution on the surface of TPU/BNNSs thermally conductive composite membrane material by spraying method based on the composite with optimized thermal management capability.Hydrophobic SiO2 particles were used to construct surface roughness and polydimethylsiloxane(PDMS)to reduce the surface energy.The effects of BNNSs dispersion concentration on the microscopic morphology and thermal conductivity of TPU/BNNSs thermally conductive composite membrane materials were investigated.The mass ratio of PDMS and SiO2 particles to obtain the best superhydrophobicity was studied,and the stability of thermal conductivity and superhydrophobicity was examined by stretching and bending experiments.Results show that the TPU/BNNSs/PDMS/SiO2 composite membrane material with synergistic cooperation of thermally conductive and superhydrophobicity can be produced when the BNNSs dispersion concentration is 6 mg/mL and the PDMS/SiO2 mass ratio is 1:1.5.The thermal conductivity of the obtained composite is 7.19 W/m·K,and the contact angle of water droplets on its surface is 169.4° and the sliding angle is 2.7°.After the stretching and bending experiments,thermal conductivity of the obtained composite are 6.97 W/m·K and 6.83 W/m·K,respectively(with only 3%and 5%of depreciation rate);the contact angles are 162.7° and 159.3°,respectively,which still possess superhydrophobicity.In the thermal management applications,the obtained composite can achieve a cooling performance close to 10℃ and exhibit excellent thermal management capability.Further,the differences in thermal management capability of the obtained composite and the non-hydrophobic thermally conductive TPU/BNNSs composite membrane material after being influenced by solid particle and liquid substance were investigated and compared.Results show that cooling performance of the non-hydrophobic thermally conductive TPU/BNNSs composite membrane material is weakened by 5.18℃ after being influenced by solid particle contamination,and its thermal management capability is complete loss after being influenced by liquid substance.However,thermally conductive and superhydrophobic TPU/BNNSs/PDMS/SiO2 composite membrane material exhibits excellent stability as the cooling performance under the influence of solid particle and liquid substance are only weakened by 0.16℃and 0.41℃,respectively,compared to the initial state.This indicates that the existence of superhydrophobicity maintains the stability of thermal management capacity.In summary,the relationship between the distribution state of thermally conductive fillers,the construction of thermally conductive pathways and the structure of thermally conductive network inside the polymer,and the thermally conductive mechanism were investigated by designing and regulating the microstructure of thermally conductive fillers inside the polymer.The preparation of thermally conductive and superhydrophobic polymer-based composites with synergistic cooperation of thermal management capability and superhydrophobicity was established by using low surface energy substance and constructing micro and nano double-order rough structures on the material surface.Superhydrophobicity was used to assist the thermally conductive polymer-based composites to solve the disturbance from external environment,maintain stable thermal management capability and lengthen the service life,then provide a certain experimental foundation for the development and application of modern electronic products.