Consistent Thermal Conductivities of Spring-Like Structured Polydimethylsiloxane Composites under Large Deformation.

Flexible and highly thermally conductive materials with consistent thermal conductivity (λ) during large deformation are urgently required to address the heat accumulation in flexible electronics. In this study, spring-like thermal conduction pathways of silver nanowire (S-AgNW) fabricated by 3D printing are compounded with polydimethylsiloxane (PDMS) to prepare S-AgNW/PDMS composites with excellent and consistent λ during deformation. The S-AgNW/PDMS composites exhibit a λ of 7.63 W m-1 K-1 at an AgNW amount of 20 vol%, which is ≈42 times that of PDMS (0.18 W m-1 K-1) and higher than that of AgNW/PDMS composites with the same amount and random dispersion of AgNW (R-AgNW/PDMS) (5.37 W m-1 K-1). Variations in the λ of 20 vol% S-AgNW/PDMS composites are less than 2% under a deformation of 200% elongation, 50% compression, or 180° bending, which benefits from the large deformation characteristics of S-AgNW. The heat-transfer coefficient (0.29 W cm-2 K-1) of 20 vol% S-AgNW/PDMS composites is ≈1.3 times that of the 20 vol% R-AgNW/PDMS composites, which reduces the temperature of a full-stressed central processing unit by 6.8 °C compared to that using the 20 vol% R-AgNW/PDMS composites as a thermally conductive material in the central processing unit.

Highly Thermally Conductive Aramid Nanofiber Composite Films with Synchronous Visible/Infrared Camouflages and Information Encryption.

The development of highly thermally conductive composites that combine visible light/infrared camouflage and information encryption has been endowed with great significance in facilitating the application of 5G communication technology in military fields. This work uses aramid nanofibers (ANF) as the matrix, hetero-structured silver nanowires@boron nitride nanosheets (AgNWs@BNNS) prepared by in situ growth as fillers, which are combined to fabricate sandwich structured thermally conductive and electrically insulating (BNNS/ANF)-(AgNWs@BNNS)-(BNNS/ANF) (denoted as BAB) composite films by "filtration self-assembly, air spraying, and hot-pressing" method. When the mass ratio of AgNWs@BNNS to BNNS is 1 : 1 and the total mass fraction is 50 wt %, BAB composite film has the maximum in-plane thermal conductivity coefficient (λ∥ of 10.36 W/(m ⋅ K)), excellent electrical insulation (breakdown strength and volume resistivity of 41.5 kV/mm and 1.21×1015â€…Ω â‹… cm, respectively) and mechanical properties (tensile strength of 170.9 MPa). 50 wt % BAB composite film could efficiently reduce the equilibrium temperature of the central processing unit (CPU) working at full power, resulting in 7.0 °C lower than that of the CPU solely integrated with ANF directly. In addition, BAB composite film boasts adaptive visible light/infrared dual camouflage properties on cement roads and jungle environments, as well as the function of fast encryption of QR code information within 24 seconds.

Flexible and Robust Functionalized Boron Nitride/Poly(p-Phenylene Benzobisoxazole) Nanocomposite Paper with High Thermal Conductivity and Outstanding Electrical Insulation.

With the rapid development of 5G information technology, thermal conductivity/dissipation problems of highly integrated electronic devices and electrical equipment are becoming prominent. In this work, "high-temperature solid-phase & diazonium salt decomposition" method is carried out to prepare benzidine-functionalized boron nitride (m-BN). Subsequently, m-BN/poly(p-phenylene benzobisoxazole) nanofiber (PNF) nanocomposite paper with nacre-mimetic layered structures is prepared via sol-gel film transformation approach. The obtained m-BN/PNF nanocomposite paper with 50 wt% m-BN presents excellent thermal conductivity, incredible electrical insulation, outstanding mechanical properties and thermal stability, due to the construction of extensive hydrogen bonds and π-π interactions between m-BN and PNF, and stable nacre-mimetic layered structures. Its λ∥ and λ⊥ are 9.68 and 0.84 W m-1 K-1, and the volume resistivity and breakdown strength are as high as 2.3 × 1015 Ω cm and 324.2 kV mm-1, respectively. Besides, it also presents extremely high tensile strength of 193.6 MPa and thermal decomposition temperature of 640 °C, showing a broad application prospect in high-end thermal management fields such as electronic devices and electrical equipment.

Electric-Field-Induced Alignment of Functionalized Carbon Nanotubes Inside Thermally Conductive Liquid Crystalline Polyimide Composite Films.

The positive liquid crystals, 4'-heptyl-4-biphenylcarbonitrile (7CB), are used to functionalize carbon nanotubes (LC-CNT), which can be aligned in the liquid crystalline polyimide (LC-PI) matrix under an alternating electric field to fabricate the thermally conductive LC-CNT/LC-PI composite films. The efficient establishment of thermal conduction pathways in thermally conductive LC-CNT/LC-PI composite films with a low amount of LC-CNT is achieved through the oriented alignment of LC-CNT within the LC-PI matrix. When the mass fraction of LC-CNT is 15 wt %, the in-plane thermal conductivity coefficient (λ∥ ) and the through-plane thermal conductivity coefficient (λ⊥ ) of the LC-CNT/LC-PI composite films reach 4.02 W/(m ⋅ K) and 0.55 W/(m⋅K), which are 90.5 % and 71.9 % higher than those of the intrinsically thermally conductive LC-PI films respectively, also 28.8 % and 5.8 % higher than those of the CNT/LC-PI composite films respectively. Meanwhile, the thermally conductive LC-CNT/LC-PI composite films also possess excellent mechanical and heat resistance properties. The Young's modulus and the heat resistance index are 2.3 GPa and 297.7 °C, respectively, which are higher than the intrinsically thermally conductive LC-PI films and the thermally conductive CNT/LC-PI composite films under the same amount of CNT.

Advances and mechanisms in polymer composites toward thermal conduction and electromagnetic wave absorption.

Polymer composites have essential applications in electronics due to their versatility, stable performance, and processability. However, with the increasing miniaturization and high power of electronics in the 5G era, there are significant challenges related to heat accumulation and electromagnetic wave (EMW) radiation in narrow spaces. Traditional solutions involve using either thermally conductive or EMW absorbing polymer composites, but these fail to meet the demand for multi-functional integrated materials in electronics. Therefore, designing thermal conduction and EMW absorption integrated polymer composites has become essential to solve the problems of heat accumulation and electromagnetic pollution in electronics and adapt to its development trend. Researchers have developed different approaches to fabricate thermal conduction and EMW absorption integrated polymer composites, including integrating functional fillers with both thermal conduction and EMW absorption functions and innovating processing methods. This review summarizes the latest research progress, factors that affect performance, and the mechanisms of thermal conduction and EMW absorption integrated polymer composites. The review also discusses problems that limit the development of these composites and potential solutions and development directions. The aim of this review is to provide references for the development of thermal conduction and EMW absorption integrated polymer composites.

Controlled Distributed Ti3 C2 Tx Hollow Microspheres on Thermally Conductive Polyimide Composite Films for Excellent Electromagnetic Interference Shielding.

Flexible multifunctional polymer-based electromagnetic interference (EMI) shielding composite films have important applications in the fields of 5G communication technology, wearable electronic devices, and artificial intelligence. Based on the design of a porous/multilayered structure and using polyimide (PI) as the matrix and polymethyl methacrylate (PMMA) microspheres as the template, flexible (Fe3 O4 /PI)-Ti3 C2 Tx -(Fe3 O4 /PI) composite films with controllable pore sizes and distribution of Ti3 C2 Tx hollow microspheres are successfully prepared by sacrificial template method. Owing to the porous/multilayered structure, when the pore size of the Ti3 C2 Tx hollow microspheres is 10 µm and the mass ratio of PMMA/Ti3 C2 Tx is 2:1, the (Fe3 O4 /PI)-Ti3 C2 Tx -(Fe3 O4 /PI) composite film has the most excellent EMI shielding performance, with EMI shielding effectiveness (EMI SE) of 85 dB. It is further verified by finite element simulation that the composite film has an excellent shielding effect on electromagnetic waves. In addition, the composite film has good thermal conductivity (thermal conductivity coefficient of 3.49 W (m·K)-1 ) and mechanical properties (tensile strength of 65.3 MPa). This flexible (Fe3 O4 /PI)-Ti3 C2 Tx -(Fe3 O4 /PI) composite film with excellent EMI shielding performance, thermal conductivity, and mechanical properties has demonstrated great potential for applications in EMI shielding protection for high-power, portable, and wearable flexible electronic devices.

Multifunctional Thermally Conductive Composite Films Based on Fungal Tree-like Heterostructured Silver Nanowires@Boron Nitride Nanosheets and Aramid Nanofibers.

Thermal conduction for electronic equipment has grown in importance in light of the burgeoning of 5G communication. It is imperatively desired to design highly thermally conductive fillers and polymer composite films with prominent Joule heating characteristics and extensive mechanical properties. In this work, "solvothermal & in situ growth" method is carried out to prepare "Fungal tree"-like hetero-structured silver nanowires@boron nitride nanosheet (AgNWs@BNNS) thermally conductive fillers. The thermally conductive AgNWs@BNNS/ANF composite films are obtained by the method of "suction filtration self-assembly and hot-pressing". When the mass fraction of AgNWs@BNNS is 50 wt%, AgNWs@BNNS/ANF composite film presents the optimal thermal conductivity coefficient of 9.44 W/(m ⋅ K) and excellent tensile strength of 136.6 MPa, good temperature-voltage response characteristics, superior electrical stability and reliability, which promise a wide application potential in 5G electronic devices.

Enhanced Thermal Conductivities of Liquid Crystal Polyesters from Controlled Structure of Molecular Chains by Introducing Different Dicarboxylic Acid Monomers.

Enhancing thermal conductivity coefficient (λ) of liquid crystal polyesters would further widen their application in electronics and electricals. In this work, a kind of biphenyl-based dihydroxy monomer is synthesized using 4, 4'-biphenyl (BP) and triethylene glycol (TEG) as raw material, which further reacts with three different dicarboxylic acids (succinic acid, p-phenylenediacetic acid, and terephthalic acid, respectively) by melt polycondensation to prepare intrinsically highly thermally conductive poly 4', 4"'-[1, 2-ethanediyl-bis(oxy-2, 1-ethanediyloxy)]-bis(p-hydroxybiphenyl) succinate (PEOS), poly 4', 4"'-[1, 2-ethanediyl-bis(oxy-2, 1-ethanediyloxy)]-bis(p-hydroxybiphenyl) p-phenyldiacetate (PEOP) and poly 4', 4"'-[1, 2-ethanediyl-bis(oxy-2, 1-ethanediyloxy)]-bis(p-hydroxybiphenyl) terephthalate (PEOT), collectively called biphenyl-based liquid crystal polyesters (B-LCPE). The results show that B-LCPE possess the desired molecular structure, exhibit smectic phase in liquid crystal range and semicrystalline polymers at room temperature, and possess excellent intrinsic thermal conductivities, thermal stabilities, and mechanical properties. λ of PEOT is 0.51 W/(m·K), significantly exceeds that of polyethylene terephthalate (0.15 W/(m·K)) which has similar molecular structure with PEOT, and also higher than that of PEOS (0.32 W/(m·K)) and PEOP (0.38 W/(m·K)). The corresponding heat resistance index (T HRI), elasticity modulus, and hardness of PEOT are 174.6°C, 3.6 GPa, and 154.5 MPa, respectively, and also higher than those of PEOS (162.2°C, 1.8 GPa, and 83.4 MPa) and PEOP (171.8°C, 2.3 GPa, and 149.6 MPa).

Flexible Ti3C2T x /(Aramid Nanofiber/PVA) Composite Films for Superior Electromagnetic Interference Shielding.

Multifunctional electromagnetic interference (EMI) shielding materials would solve electromagnetic radiation and pollution problems from electronic devices. Herein, the directional freeze-drying technology is utilized to prepare the aramid nanofiber/polyvinyl alcohol aerogel with a directionally porous structure (D-ANF/PVA), and the Ti3C2T x dispersion is fully immersed into the D-ANF/PVA aerogel via ultrasonication and vacuum-assisted impregnation. Ti3C2T x /(ANF/PVA) EMI shielding composite films with directionally ordered structure (D-Ti3C2T x /(ANF/PVA)) are then prepared by freeze-drying and hot pressing. Constructing a directionally porous structure enables the highly conductive Ti3C2T x nanosheets to be wrapped on the directionally porous D-ANF/PVA framework in order arrangement and overlapped with each other. And the hot pressing process effectively reduces the layer spacing between the stacked wavy D-ANF/PVA, to form a large number of Ti3C2T x -Ti3C2T x continuous conductive paths, which significantly improves the conductivity of the D-Ti3C2T x /(ANF/PVA) EMI shielding composite film. When the amount of Ti3C2T x is 80 wt%, the EMI shielding effectiveness (EMI SE) and specific SE (SSE/t) of D-Ti3C2T x /(ANF/PVA) EMI shielding composite film achieve 70 dB and 13790 dB·cm2·g-1 (thickness and density of 120 µm and 0.423 g·cm-3), far superior to random-structured Ti3C2T x /(ANF/PVA) (R-Ti3C2T x /(ANF/PVA)) composite film (46 dB and 9062 dB·cm2·g-1, respectively) via blending-freeze-drying followed by hot pressing technology. Meanwhile, the D-Ti3C2T x /(ANF/PVA) EMI shielding composite film possesses excellent flexibility and foldability.

Pressure-Induced Self-Interlocked Structures for Expanded Graphite Composite Papers Achieving Prominent EMI Shielding Effectiveness and Outstanding Thermal Conductivities.

High-performance films via layer-by-layer assembly of two-dimensional (2D) materials would provide all possibilities for the development of modern integrated electronics. However, the stacked structure between nanosheets and large-scale fabrication still remain a great challenge. Herein, Fe3O4/expanded graphite (EG) papers are fabricated via in situ oxidation of ferrocene onto EG nanosheets, followed by a continuous roll-in process. Upon mechanical compaction, the self-interlocked structures driven by close overlapping and hooking of nanosheets in Fe3O4/EG (FG) composites remarkably facilitate the construction of phonon and electron transmission channels and improve mechanical strength. FG papers exhibit prominent shielding effectiveness (67.1 dB at ∼100 µm) with enhanced absorptivity (∼0.1, surpassing lots of conductive film materials), stemming from the synergistic effect of electrical and magnetic properties. Also, the electromagnetic interference (EMI) shielding performance shows prominent reliability after bending (2000 cycles) and ultrasonic treatment (30 min). The corresponding tensile strength reaches 35.8 MPa; meanwhile, the corresponding in-plane thermal conductivity coefficient is as high as 191.7 W/(m·K), which can rapidly and efficiently accelerate heat dissipation. In particular, FG papers also reveal rapid response, controllable, and highly stable Joule heating performance and present promising prospects in the fields of radiation-proof clothing, flexible heaters, portable wearable devices, and aerospace.

Discotic Liquid Crystal Epoxy Resins Integrating Intrinsic High Thermal Conductivity and Intrinsic Flame Retardancy.

The integration of intrinsic thermal conductivity and intrinsic flame retardancy of epoxy resins shows wider application prospects in electricals and electronics. Discotic liquid crystal epoxy (D-LCE) is synthesized from pyrocatechol, 2-allyloxyethanol, and 3-chloroperoxybenzoic acid. P/Si synergistic flame-retardant co-curing agent (DOPO-POSS, DP) is synthesized from p-hydroxybenzaldehyde, 9, 10-dihydro-9-oxa-10-phosphaphenanthrene 10-oxide (DOPO), and amino terminated polysilsesquioxane (POSS). Finally, D-LCE is cured within liquid crystal range with 4, 4'-diaminodiphenyl methane (DDM) and DP, to obtain intrinsic highly thermal conductive/flame-retardant epoxy resins (D-LCERDP ). D-LCERDP-10.0 (10.0 wt% DP) synchronously possesses excellent intrinsic thermal conductivity and intrinsic flame retardancy, with thermal conductivity coefficient in vertical and parallel direction (λ⊥ and λ∥ ) of 0.34 and 1.30 W m-1 K-1 , much higher than that of general bisphenol A epoxy resin (E-51, λ⊥ of 0.19 W m-1 K-1 , λ∥ of 0.65 W m-1 K-1 ). The limiting oxygen index (LOI) value of D-LCERDP-10.0 reaches 31.1, also better than those of E-51 (19.8) and D-LCER (21.3).

Hierarchically Multifunctional Polyimide Composite Films with Strongly Enhanced Thermal Conductivity.

The development of lightweight and integration for electronics requires flexible films with high thermal conductivity and electromagnetic interference (EMI) shielding to overcome heat accumulation and electromagnetic radiation pollution. Herein, the hierarchical design and assembly strategy was adopted to fabricate hierarchically multifunctional polyimide composite films, with graphene oxide/expanded graphite (GO/EG) as the top thermally conductive and EMI shielding layer, Fe3O4/polyimide (Fe3O4/PI) as the middle EMI shielding enhancement layer and electrospun PI fibers as the substrate layer for mechanical improvement. PI composite films with 61.0 wt% of GO/EG and 23.8 wt% of Fe3O4/PI exhibits high in-plane thermal conductivity coefficient (95.40 W (m K)-1), excellent EMI shielding effectiveness (34.0 dB), good tensile strength (93.6 MPa) and fast electric-heating response (5 s). The test in the central processing unit verifies PI composite films present broad application prospects in electronics fields.

Flexible Sandwich-Structured Electromagnetic Interference Shielding Nanocomposite Films with Excellent Thermal Conductivities.

With the rapid development and popularization of smart, portable, and wearable flexible electronic devices, urgent demands have been raised for flexible electromagnetic interference (EMI) shielding films to solve related electromagnetic pollution problems. With polyvinyl alcohol (PVA) as polymer matrix, the sandwich-structured EMI shielding nanocomposite films are prepared via electrospinning-laying-hot pressing technology, where Fe3 O4 /PVA composite electrospun nanofibers in the top and bottom layers and Ti3 C2 Tx /PVA composite electrospun nanofibers in the middle layer. Owing to the electrospinning process and the successful construction of the sandwich structure, when the amounts of Ti3 C2 Tx and Fe3 O4 are respectively only 13.3 and 26.7 wt%, the EMI shielding effectiveness (EMI SE) of the sandwich-structured EMI shielding nanocomposite films reach 40 dB with the thickness of 75 µm, higher than that of (Fe3 O4 /Ti3 C2 Tx )/PVA EMI shielding nanocomposite films (21 dB) prepared based on blending-electrospinning-hot pressing process under the same amounts of fillers. Furthermore, the prepared sandwich-structured EMI shielding nanocomposite films possess excellent thermal conductivities and mechanical properties. This novel kind of flexible sandwich-structured EMI shielding nanocomposite films with excellent EMI shielding performances, thermal conductivities, and mechanical properties presents broad application prospects in the fields of EMI shielding and protection for high-power, portable, and wearable flexible electronic devices.

Breaking Through Bottlenecks for Thermally Conductive Polymer Composites: A Perspective for Intrinsic Thermal Conductivity, Interfacial Thermal Resistance and Theoretics.

Rapid development of energy, electrical and electronic technologies has put forward higher requirements for the thermal conductivities of polymers and their composites. However, the thermal conductivity coefficient (λ) values of prepared thermally conductive polymer composites are still difficult to achieve expectations, which has become the bottleneck in the fields of thermally conductive polymer composites. Aimed at that, based on the accumulation of the previous research works by related researchers and our research group, this paper proposes three possible directions for breaking through the bottlenecks: (1) preparing and synthesizing intrinsically thermally conductive polymers, (2) reducing the interfacial thermal resistance in thermally conductive polymer composites, and (3) establishing suitable thermal conduction models and studying inner thermal conduction mechanism to guide experimental optimization. Also, the future development trends of the three above-mentioned directions are foreseen, hoping to provide certain basis and guidance for the preparation, researches and development of thermally conductive polymers and their composites.

Lightweight, Flexible Cellulose-Derived Carbon Aerogel@Reduced Graphene Oxide/PDMS Composites with Outstanding EMI Shielding Performances and Excellent Thermal Conductivities.

In order to ensure the operational reliability and information security of sophisticated electronic components and to protect human health, efficient electromagnetic interference (EMI) shielding materials are required to attenuate electromagnetic wave energy. In this work, the cellulose solution is obtained by dissolving cotton through hydrogen bond driving self-assembly using sodium hydroxide (NaOH)/urea solution, and cellulose aerogels (CA) are prepared by gelation and freeze-drying. Then, the cellulose carbon aerogel@reduced graphene oxide aerogels (CCA@rGO) are prepared by vacuum impregnation, freeze-drying followed by thermal annealing, and finally, the CCA@rGO/polydimethylsiloxane (PDMS) EMI shielding composites are prepared by backfilling with PDMS. Owing to skin-core structure of CCA@rGO, the complete three-dimensional (3D) double-layer conductive network can be successfully constructed. When the loading of CCA@rGO is 3.05 wt%, CCA@rGO/PDMS EMI shielding composites have an excellent EMI shielding effectiveness (EMI SE) of 51 dB, which is 3.9 times higher than that of the co-blended CCA/rGO/PDMS EMI shielding composites (13 dB) with the same loading of fillers. At this time, the CCA@rGO/PDMS EMI shielding composites have excellent thermal stability (THRI of 178.3 °C) and good thermal conductivity coefficient (λ of 0.65 W m-1 K-1). Excellent comprehensive performance makes CCA@rGO/PDMS EMI shielding composites great prospect for applications in lightweight, flexible EMI shielding composites.

Significant Reduction of Interfacial Thermal Resistance and Phonon Scattering in Graphene/Polyimide Thermally Conductive Composite Films for Thermal Management.

The developing flexible electronic equipment are greatly affected by the rapid accumulation of heat, which is urgent to be solved by thermally conductive polymer composite films. However, the interfacial thermal resistance (ITR) and the phonon scattering at the interfaces are the main bottlenecks limiting the rapid and efficient improvement of thermal conductivity coefficients (λ) of the polymer composite films. Moreover, few researches were focused on characterizing ITR and phonon scattering in thermally conductive polymer composite films. In this paper, graphene oxide (GO) was aminated (NH2-GO) and reduced (NH2-rGO), then NH2-rGO/polyimide (NH2-rGO/PI) thermally conductive composite films were fabricated. Raman spectroscopy was utilized to innovatively characterize phonon scattering and ITR at the interfaces in NH2-rGO/PI thermally conductive composite films, revealing the interfacial thermal conduction mechanism, proving that the amination optimized the interfaces between NH2-rGO and PI, reduced phonon scattering and ITR, and ultimately improved the interfacial thermal conduction. The in-plane λ (λ ||) and through-plane λ (λ ⊥) of 15 wt% NH2-rGO/PI thermally conductive composite films at room temperature were, respectively, 7.13 W/mK and 0.74 W/mK, 8.2 times λ || (0.87 W/mK) and 3.5 times λ ⊥ (0.21 W/mK) of pure PI film, also significantly higher than λ || (5.50 W/mK) and λ ⊥ (0.62 W/mK) of 15 wt% rGO/PI thermally conductive composite films. Calculation based on the effective medium theory model proved that ITR was reduced via the amination of rGO. Infrared thermal imaging and finite element simulation showed that NH2-rGO/PI thermally conductive composite films obtained excellent heat dissipation and efficient thermal management capabilities on the light-emitting diodes bulbs, 5G high-power chips, and other electronic equipment, which are easy to generate heat severely.

Multifunctional Flexible Electromagnetic Interference Shielding Silver Nanowires/Cellulose Films with Excellent Thermal Management and Joule Heating Performances.

Flexible electromagnetic interference (EMI) shielding materials with excellent thermal conductivities and Joule heating performances are of urgent demand in the communication industry, artificial intelligence, and wearable electronics. In this work, highly conductive silver nanowires (AgNWs) were prepared using the polyol method. Cellulose sheets were then prepared by dissolving natural cotton in a green and efficient NaOH/urea aqueous solution. Finally, multifunctional flexible EMI shielding AgNWs/cellulose films were fabricated based on vacuum-assisted filtration and hot-pressing. AgNWs are evenly embedded in the inner cellulose matrix and overlap with each other to form a 3D network. AgNWs/cellulose films, with a thickness of 44.5 µm, obtain the superior EMI shielding effectiveness of 101 dB, which is the highest value ever reported for shielding materials with the same thickness. In addition, AgNWs/cellulose films present excellent tensile strength (60.7 MPa) and tensile modulus (3.35 GPa), ultrahigh electrical conductivity (σ, 5571 S/cm), and excellent in-plane thermal conductivity coefficient (λ∥, 10.55 W/mK), which can effectively dissipate the heat accumulation. Interestingly, AgNWs/cellulose films also show outstanding Joule heating performances, good stability, and sensitive temperature response at driving voltages, absolutely safe for the human body. Therefore, our fabricated multifunctional flexible AgNWs/cellulose films have broad prospects in the fields of EMI shielding and protection of outdoor large-scale power transformers and wearable electronics.

Highly Thermal Conductivities, Excellent Mechanical Robustness and Flexibility, and Outstanding Thermal Stabilities of Aramid Nanofiber Composite Papers with Nacre-Mimetic Layered Structures.

Aramid nanofiber (ANF) paper has shown potential applications in flexible electronics. However, its inherent low thermal conductivity coefficient (λ) values might threaten the safety of devices under a high-power working condition. In this work, polydopamine-functionalized boron nitride nanosheet (BNNS@PDA)/ANF thermally conductive composite papers with nacre-mimetic layered structures were prepared via highly efficient vacuum-assisted filtration followed by hot pressing. For a given BNNS loading, the surface functionalization of BNNS could further enhance the thermal conductivities and mechanical properties of BNNS@PDA/ANF composite papers. BNNS@PDA/ANF composite papers presented anisotropic thermal conductivities, and the through-plane (λ⊥) and in-plane (λ∥) values of the 50 wt % BNNS@PDA/ANF composite papers reached 0.62 and 3.94 W/mK, 181.8 and 196.2% higher than those of original ANF paper, respectively, which were also higher than those of 50 wt % BNNS/ANF composite papers (λ⊥ = 0.52 W/mK and λ∥ = 3.33 W/mK). The tensile strength of the 50 wt % BNNS@PDA/ANF composite papers reached 36.8 MPa, 30.5% higher than that of 50 wt % BNNS/ANF composite papers (28.2 MPa). In addition, the heat resistance index (THRI) of the 50 wt % BNNS@PDA/ANF composite papers was further increased to 223.1 °C. Overall, our fabricated BNNS@PDA/ANF composite papers possess highly thermal conductivities, excellent mechanical robustness and flexibility, and outstanding thermal stabilities, showing great potential applications in the fields of intelligent wearable equipment, flexible supercapacitors, and flexible electronics.

Reduced Graphene Oxide Heterostructured Silver Nanoparticles Significantly Enhanced Thermal Conductivities in Hot-Pressed Electrospun Polyimide Nanocomposites.

Graphene presents an extremely ultra-high thermal conductivity, well above other known thermally conductive fillers. However, graphene tends to aggregate easily due to its strong intermolecular π-π interaction, resulting in poor dispersion in the polymer matrix. In this study, silver nanoparticles anchored reduced graphene oxide (Ag/rGO) were first prepared using one-pot synchronous reduction of Ag+ and GO solution via glucose. The thermally conductive (Ag/rGO)/polyimide ((Ag/rGO)/PI) nanocomposites were then obtained via electrospinning the in situ polymerized (Ag/rGO)/polyamide electrospun suspension followed by a hot-press technique. The thermal conductivity (λ), glass transition temperature (Tg), and heat resistance index (THRI) of the (Ag/rGO)/PI nanocomposites all increased with increasing the loading of Ag/rGO fillers. When the mass fraction of Ag/rGO (the weight ratio of rGO to Ag was 4:1) fillers was 15%, the corresponding (Ag/rGO)/PI nanocomposites showed a maximum λ of 2.12 W/(m K). The corresponding Tg and THRI values were also enhanced to 216.1 and 298.6 °C, respectively. Furthermore, thermal conductivities calculated by our established improved thermal conduction model were relatively closer to the experimental results than the results obtained from other classical models.