Emerging Flexible Thermally Conductive Films:Mechanism,Fabrication,Application

Effective thermal management is quite urgent for electronics owing to their ever-growing integration degree,operation frequency and power density,and the main strategy of thermal management is to remove excess energy from electronics to outside by thermal conductive materials.Compared to the conventional thermal management materials,flexible thermally conductive films with high in-plane thermal conductivity,as emerging candidates,have aroused greater interest in the last decade,which show great potential in thermal management applications of next-generation devices.However,a comprehensive review of flexible thermally conductive films is rarely reported.Thus,we review recent advances of both intrinsic polymer films and polymer-based composite films with ultrahigh in-plane thermal conductivity,with deep understandings of heat transfer mechanism,processing methods to enhance thermal conductivity,optimization strategies to reduce interface thermal resistance and their potential applications.Lastly,challenges and opportunities for the future development of flexible thermally conductive films are also discussed.

Janus(BNNS/ANF)-(AgNWs/ANF)thermal conductivity composite films with superior electromagnetic interference shielding and Joule heating performances

Highly thermal conductivity materials with excellent electromagnetic interference shielding and Joule heating performances are ideal for thermal management in the next generation of communication industry,artificial intelligence and wearable electronics.In this work,silver nanowires(AgNWs)are prepared using silver nitrate as the silver source and ethylene glycol as the solvent and reducing agent,and boron nitride(BN)is performed to prepare BN nanosheets(BNNS)with the help of isopropyl alcohol and ultrasonication-assisted peeling method,which are compounded with aramid nanofibers(ANF)prepared by chemical dissociation,respectively,and the(BNNS/ANF)-(AgNWs/ANF)thermal conductivity and electromagnetic interference shielding composite films with Janus structures are prepared by the"vacuum-assisted filtration and hot-pressing"method.Janus(BNNS/ANF)-(AgNWs/ANF)composite films exhibit"one side insulating,one side conducting"performance,the surface resistivity of the BNNS/ANF surface is 4.7×10^(13) Ω,while the conductivity of the AgNWs/ANF surface is 5,275 S/cm.And Janus(BNNS/ANF)-(AgNWs/ANF)composite film with thickness of 95 pm has a high in-plane thermal conductivity coefficient of 8.12 W/(m·K)and superior electromagnetic interference shielding effectiveness of 70 dB.The obtained composite film also has excellent tensile strength of 122.9 MPa and tensile modulus and 2.7 GPa.It also has good temperature-voltage response characteristics(high Joule heating temperature at low supply voltage(5 V,215.0℃),fast response time(10 s)),excellent electrical stability and reliability(stable and constant real-time relative resistance under up to 300 cycles and 1,500 s of tensile-bending fatigue work tests).

Enhancing the thermal conductivity of nanofibrillated cellulose films with 1D BN belts formed by in-situ generation and sintering of BN nanosheets

The rapid miniaturization and high integration of modern electronic devices have brought an increasing demand for polymer-based thermal management materials with higher thermal conductivity.Boron nitride nanosheets(BNNs)have been widely used as thermally conductive fillers benefiting from the extremely high intrinsic thermal conductivity.However,the small lateral size and weak interface bonding of BNNs enabled them to only form thermally conductive networks through physical overlap,resulting in high interfacial thermal resistance.To address this issue,an innovative strategy based on interface engineering was proposed in this study.High-aspect-ratio boron nitride belts(BNbs)were successfully synthesized by carbon thermal reduction nitridation method through the in-situ generation and sintering of BNNs.The surface of BNb showed the sintering of numerous smaller-sized BNNs,which precisely addresses the issue of weak interfacial bonding between BNNs.On this basis,the as-synthesized BNbs were combined with nano-fibrillated cellulose(NFC)to prepare NFC/BNb composite films through a facile vacuum filtration process.Due to the thermally conductive network formed by the horizontal oriented arrangement of BNb and their particular morphological advantages,the NFC/BNb films demonstrated significantly higher in-plane thermal conductivity than that of NFC/BNNs films,achieving the highest value of 19.119 W·m^(−1)·K^(−1) at a 20 wt%filling fraction.In addition,the NFC/BNb films also exhibited superior thermal stability,mechanical strength,flexibility,and electrical insulation performance,suggesting the significant application potential of the designed BNb fillers in the thermal management field.