Development and Perspectives of Thermal Conductive Polymer Composites

Poly(ε-caprolactone-co-ε-decalactone)/carbon black or carbon nanofiber composites. Synthesis, morphological, and thermal/electrical properties

Much of the research on biodegradable polymers is currently aimed at developing alternative materials to fossil fuel plastics. Among the biodegradable polymers, the bio-based aliphatic polyesters (e.g. poly-ε-caprolactone, PCL) have had important success in replacing single-use plastics as well as durable consumer goods, mainly in the packaging and biomedical sectors. In other sectors, like electronics, the use of bio-based plastics has received little attention, despite e-waste (pollutant and difficult to handle) being the fastest growing solid waste stream in the world. In this work, P(CL-DL)/carbon black and P(CL-DL)/carbon nanofiber composites with enhanced thermal and electrical properties were prepared and studied. P(CL-DL) copolymers were synthesized via ring opening polymerization (ROP) at CL/DL molar compositions of 95/5, 90/10, 80/20, and 70/30. Their number-average molecular weight (M̄ n) and dispersity index (Đ) lie between 17.5 and 21.8 kDa, and 1.72 and 1.99, respectively. They are thermally stable to up to 300 °C, and show a melting temperature (T m) and a crystalline degree (X c) that decrease with increasing contents of DL in the polymer chains. The thermal (k) and electrical (σ) conductivities of copolymers were enhanced by adding, through melt blending, carbon black (CB) or carbon nanofibers (CNF) at 1.25, 2.5, and 5.0 wt%, reaching a maximum value of 0.55 W m-1 K-1 and 10-7 S cm-1, respectively. The frequency-dependence of the dielectric constant (ε') and dielectric losses (tan δ) was also measured. Two of the composites showed a marked increase of ε' near percolation whereas their tan δ remained low. The thermal and electrical conductivity performances, as well as the increment found in ε' near percolation, are discussed in terms morphology changes produced by variations in both the DL mol% and the nanoparticles wt%. Finally, biodegradable composites with heat and electron dissipative capacities are materials that can contribute to alleviating the problem of e-waste.

Molecular-Level Interface Engineering and Additive-Induced Crystallinity Tuning for High-Performance Thermally Conductive Polymer Composites

To boost up the properties of thermally conductive polymer composites, it is essential to conduct comprehensive research focused on interface engineering between the polymer matrix and fillers. Hexagonal boron nitride (BN) or expanded graphite (EG) are commonly utilized as nanofillers to improve the thermal conductivity of polymer composites. However, the interfacial interactions between the polymer matrix and nanofillers are generally weak, making effective thermal conductivity challenging. To address this issue, we have designed and synthesized an electron-rich and aromatic tetrathiafulvalene-based reactive mesogen (TRM), which not only possesses high thermal conductivity but also exhibits excellent interfacial affinity with BN and EG at the molecular level. Systematic experiments, including photophysical, thermodynamic, structural, and computational analyses, reveal that the thermal conductivity of TRM-based polymer composites is substantially enhanced due to effective interfacial interactions between TRM and fillers. The TRM composites experimentally show excellent thermal conductivity based on enhanced interfacial phonon transfer, and these results are supported by theoretical interpretations. These findings underscore the critical importance of interface engineering between the polymer matrix and fillers at the molecular level in maximizing the material properties of polymer composites.

Research on PVDF/BNNSs/MXene multilayer films with high energy density and thermal conductivity for dielectric capacitors

Polyvinylidene fluoride (PVDF) has promising applications in the field of dielectric capacitors. However, its low dielectric constant and thermal conductivity limit energy storage density. To address this, three multilayer composite topologies were designed with PVDF/boron nitride nanosheets as insulation and PVDF/MXene as polarization layers. A performance evaluation framework based on the analytic hierarchy process technique for order preference by similarity to the ideal solution method identified the insulation-polarization-polarization-insulation topology as the optimal configuration. This structure enhanced the dielectric performance (εr/tan δ) by 239.44% over pure PVDF at 103 Hz, increased thermal conductivity by 60.45%, and improved breakdown field strength. In addition, charge-discharge efficiency at 300 MV/m reached 75%, with a discharge density of 6.3 J/cm3, which is 152% higher than PVDF. The multilayer design effectively integrates the strengths of each layer to significantly enhance the overall performance, demonstrating that operational research methods are practical for evaluating dielectric materials and guiding design.

Triply periodic minimal surfaces for thermo-mechanical protection

Triply periodic minimal surface (TPMS) metamaterials show promise for thermal management systems but are challenging to integrate into existing packaging with strict mechanical requirements. Composite TPMS lattices may offer more control over thermal and mechanical properties through material and geometric tuning. Here, we fabricate copper-plated, 3D-printed triply periodic minimal surface primitive lattices and evaluate their suitability for battery thermal management systems. We measure the effects of lattice geometry and copper thickness on pressure drop, mechanical properties, and thermal conductivity. The lattices as internal filling structures in a multichannel cold plate exhibited pressure drops under 6.5 kPa at a 1 LPM flow rate. Pressure drop decreased when the number of channels (width of the cold plate) was increased. With a 0.43% copper volume loading, the lattice more than tripled in thermal conductivity but still retained a polymer-like compliance. A higher lattice relative density did not affect the thermal conductivity but caused a higher elastic modulus and compressive strength, and a stiffer cyclic loading response. The lattice design demonstrates that the structural parameters that control pressure drop, mechanical, and thermal conductivity can be decoupled, which can be used to achieve a wide range of disparate properties in complex multiphysics systems.

Bioinspired Functional Composites for Enhanced Thermally Conductivity via Fractal-Growth CuNP Fillers

Thermal conduction for electronic devices has attracted extensive attention in light of the development of 5G communication. Thermally conductive materials with high thermal conductivity and extensive mechanical flexibility are extremely desirable in practical applications. However, the construction of efficient interconnected conductive pathways and continuous conductive networks is inadequate for either processing or actual usage in existing technologies. In this work, spherical copper nanoparticles (S-CuNPs) and urchin-inspired fractal-growth CuNPs (U-CuNPs), thermally conductive metal fillers induced by ionic liquids, were fabricated successfully through the electrochemical deposition method. Compared to S-CuNPs, the U-CuNPs shows larger specific surface contact area, thus making it easier to build a continuous conductive pathway network in the corresponding U-CuNPs/liquid silicone rubber (LSR) thermally conductive composites. The optimal loading of CuNP fillers was determined by evaluating the rheological performance of the prepolymer and the mechanical properties and thermal conductivity performances of the composites. When the filler loading is 150 phr, the U-CuNPs/LSR produces optimal mechanical properties (e.g., tensile strength and modulus), thermal conductivity (above 1000% improvement compared to pure LSR), and heating/cooling efficiency. The enhanced thermal conductivity of U-CuNPs/LSR was also confirmed through the finite element analysis (FEA) overall temperature distribution, indicating that U-CuNPs with larger specific surface contact areas exhibit more advantages in forming a continuous network in composites than S-CuNPs, making U-CuNPs/LSR a promising and competitive alternative to traditional flexible thermally interface materials.

Playing with Low Amounts of Expanded Graphite for Melt-Processed Polyamide and Copolyester Nanocomposites to Achieve Control of Mechanical, Tribological, Thermal and Dielectric Properties

Polyamide 11 (PA11) and copolyester (TPC-E) were compounded through melt extrusion with low levels (below 10%) of expanded graphite (EG), aiming at the manufacturing of a thermally and electrically conductive composite resistant to friction and with acceptable mechanical properties. Thermal characterisation showed that the EG presence had no influence on the onset degradation temperature or melting temperature. While the specific density of the produced composite materials increased linearly with increasing levels of EG, the tensile modulus and flexural modulus showed a significant increase already at the introduction of 1 wt% EG. However, the elongation at break decreased significantly for higher loadings, which is typical for composite materials. We observed the increase in the dielectric and thermal conductivity, and the dissipated power displayed a much larger increase where high frequencies (e.g., 10 GHz) were taken into account. The tribological results showed significant changes at 4 wt% for the PA11 composite and 6 wt% for the TPC-E composite. Morphological analysis of the wear surfaces indicated that the main wear mechanism changed from abrasive wear to adhesive wear, which contributes to the enhanced wear resistance of the developed materials. Overall, we manufactured new composite materials with enhanced dielectric properties and superior wear resistance while maintaining good processability, specifically upon using 4-6 wt% of EG.

A Novel Polyester Varnish Nanocomposites for Electrical Machines with Improved Thermal and Dielectric Properties Using Functionalized TiO2 Nanoparticles

Recently, there has been a growing interest in polymer insulating materials that incorporate nanoscale inorganic additives, as they have shown significantly improved dielectric, thermal, and mechanical properties, making them highly suitable for application in high-voltage insulating materials for electrical machines. This study aims to improve the dielectric and thermal properties of a commercial polyester varnish by incorporating different concentrations of titanium dioxide nanoparticles (TiO2) with proper surface functionalization. Permafil 9637 dipping varnish is the varnish used for this investigation, and vinyl silane is the coupling agent used in the surface functionalization of TiO2 nanoparticles. First, nanoparticles are characterized through Fourier transform infrared spectroscopy to validate the success of their surface functionalization. Then, varnish nanocomposites are characterized through field emission scanning electron microscopy to validate the dispersion and morphology of nanoparticles within the varnish matrix. Following characterization, varnish nanocomposites are evaluated for thermal and dielectric properties. Regarding thermal properties, the thermal conductivity of the prepared nanocomposites is assessed. Regarding dielectric properties, both permittivity and dielectric losses are evaluated over a wide frequency range, starting from 20 Hz up to 2 MHz. Moreover, the AC breakdown voltage is measured for varnish nanocomposites, and the obtained data are incorporated into a finite element method to obtain the dielectric breakdown strength. Finally, the physical mechanisms behind the obtained results are discussed, considering the role of nanoparticle loading and surface functionalization.

Enhanced Thermal Conductivity and Dielectric Properties of Epoxy Composites with Fluorinated Graphene Nanofillers

The demand for high-performance dielectrics has increased due to the rapid development of modern electric power and electronic technology. Composite dielectrics, which can overcome the limitations of traditional single polymers in thermal conductivity, dielectric properties and mechanical performance, have received considerable attention. In this study, we report a multifunctional nanocomposite material fabricated by blending fluorinated graphene (F-graphene) with epoxy resin. The F-graphene/epoxy composite exhibited a high thermal conductivity of 0.3304 W·m-1·K-1 at a low filler loading of 1.0 wt.%, which was 67.63% higher than that of pure epoxy. The composite dielectric also showed high breakdown strength (78.60 kV/mm), high dielectric constant (8.23), low dielectric loss (<0.015) and low AC conductivity (<10-11 S·m-1). Moreover, the composite demonstrated high thermal stability and strong mechanical strength. It is believed that the F-graphene/epoxy composite has outstanding performance in various aspects and can enable the development and manufacturing of advanced electric power and electronic equipment devices.