Improving the thermal conductivity of epoxy resin by the addition of a mixture of graphite nanoplatelets and silicon carbide microparticles

Improving interfacial thermal transport in silicon-reinforced epoxy resin composites with self-assembled monolayers

Epoxy resin (EP) based composite materials, due to their advantages such as light weight, ease of processing, and mechanical properties, have been widely applied across thermal packaging field. However, the overall thermal conductivity is constrained by the interfacial thermal resistance between the filler and the substrate. Existing studies suggest that self-assembled monolayers (SAM) can enhance the interfacial thermal conductance (ITC) by forming covalent bonds. Nevertheless, limited research has focused on using SAM to form bilateral covalent bonds to regulate ITC. Therefore, SAM capable of forming bilateral covalent bonds at the EP/silicon (Si) interface were employed to enhance ITC. In this study, time-domain thermoreflectance (TDTR) experiments and molecular dynamics (MD) simulations were conducted to investigate the EP/SAM/Si system. The results demonstrate that SAM-NH2 modification, which forms bilateral covalent bonds at the EP/Si interface, increased the interfacial adhesion strength and enhanced ITC to 140%, thereby significantly promoting interfacial heat transfer. Conversely, ITC was reduced with SAM-CH3 due to the formation of single covalent bond. Subsequently, the differential effective medium (DEM) model was used to determine that the thermal conductivity of the composite modified with SAM-NH2 was improved by 11%. This study provides new insights into adjusting ITC using SAM.

Performance Evaluation for Ultra-Lightweight Epoxy-Based Bipolar Plate Production with Cycle Time Reduction of Reactive Molding Process

The commercial viability of fuel cells for vehicle application has been examined in the context of lightweight material options, as well as in combination with improvements in fuel cell powertrain. Investigation into ultra-lightweight bipolar plates (BPs), the main component in terms of the weight effect, is of great importance to enhance energy efficiency. This research aims to fabricate a layered carbon fiber/epoxy composite structure for BPs. Two types of carbon fillers (COOH-MWCNT and COOH-GNP) reinforced with woven carbon fiber sheets (WCFS) have been utilized. The conceptual idea is to reduce molding cycle time by improving the structural, electrical, and mechanical properties of BPs. Reducing the reactive molding cycle time is required for commercial production possibility. The desired crosslink density of 97%, observed at reactive molding time, was reduced by 83% at 140 °C processing temperature. The as-fabricated BPs demonstrate excellent electrical conductivity and mechanical strength that achieved the DOE standard. Under actual fuel cell operation, the as-fabricated BPs show superior performance to commercial furan-based composite BPs in terms of the cell potential and maximum power. This research demonstrates the practical and straightforward way to produce high-performance and reliable BPs with a rapid production rate for actual PEMFC utilization.

Physical, Thermal Transport, and Compressive Properties of Epoxy Composite Filled with Graphitic- and Ceramic-Based Thermally Conductive Nanofillers

Epoxy polymer composites embedded with thermally conductive nanofillers play an important role in the thermal management of polymer microelectronic packages, since they can provide thermal conduction properties with electrically insulating properties. An epoxy composite system filled with graphitic-based fillers; multi-walled carbon nanotubes (MWCNTs), graphene nanoplatelets (GNPs) and ceramic-based filler; silicon carbide nanoparticles (SiCs) was investigated as a form of thermal-effective reinforcement for epoxy matrices. The epoxy composites were fabricated using a simple fabrication method, which included ultrasonication and planetary centrifugal mixing. The effect of graphite-based and ceramic-based fillers on the thermal conductivity was measured by the transient plane source method, while the glass transition temperature of the fully cured samples was studied by differential scanning calorimetry. Thermal gravimetric analysis was adopted to study the thermal stability of the samples, and the compressive properties of different filler loadings (1–5 vol.%) were also discussed. The glass temperatures and thermal stabilities of the epoxy system were increased when incorporated with the graphite- and ceramic-based fillers. These results can be correlated with the thermal conductivity of the samples, which was found to increase with the increase in the filler loadings, except for the epoxy/SiCs composites. The thermal conductivity of the composites increased to 0.4 W/mK with 5 vol.% of MWCNTs, which is a 100% improvement over pure epoxy. The GNPs, SiCs, and MWCNTs showed uniform dispersion in the epoxy matrix and well-established thermally conductive pathways.

Thermal interface materials with graphene fillers: review of the state of the art and outlook for future applications

We review the current state-of-the-art graphene-enhanced thermal interface materials for the management of heat in the next generation of electronics. Increased integration densities, speed and power of electronic and optoelectronic devices require thermal interface materials with substantially higher thermal conductivity, improved reliability, and lower cost. Graphene has emerged as a promising filler material that can meet the demands of future high-speed and high-powered electronics. This review describes the use of graphene as a filler in curing and non-curing polymer matrices. Special attention is given to strategies for achieving the thermal percolation threshold with its corresponding characteristic increase in the overall thermal conductivity. Many applications require high thermal conductivity of composites, while simultaneously preserving electrical insulation. A hybrid filler approach, using graphene and boron nitride, is presented as a possible technology providing for the independent control of electrical and thermal conduction. The reliability and lifespan performance of thermal interface materials is an important consideration towards the determination of appropriate practical applications. The present review addresses these issues in detail, demonstrating the promise of graphene-enhanced thermal interface materials compared to alternative technologies.

An Approach Towards Optimization Appraisal of Thermal Conductivity of Magnetic Thermoplastic Elastomeric Nanocomposites Using Response Surface Methodology

This study investigates the optimization of thermal conductivity of nickel zinc ferrite incorporated thermoplastic natural rubber nanocomposites using response surface methodology (RSM). The experimental runs were based on face-centered central composite design (FCCD) where three levels were designated for both temperature and magnetic filler content. The analysis of variance (ANOVA) results showed that the implemented technique is significant with an F-value of 35.7 and a p-value of <0.0001. Moreover, the statistical inference drawn from the quadratic model suggests a saddle response behavior the thermal conductivity took when both factors were correlated. The factors’ optimal set confined within the practical range led to a thermal conductivity of 1.05 W/m·K, a value which is believed to be associated with an optimal percolated network that served as efficacious thermal pathways in the fabricated nanocomposites. These results are believed to contribute to the potential employability of magnetic polymer nanocomposites (MPNCs) in electronic packaging applications.

Thermal and Mechanical Behavior of Wood Plastic Composites by Addition of Graphene Nanoplatelets

Wood plastic composites (WPCs) incorporating graphene nano-platelets (GNPs) were fabricated using hot-pressed technology to enhance thermal and mechanical behavior. The influences of thermal filler content and temperature on the thermal performance of the modified WPCs were investigated. The results showed that the thermal conductivity of the composites increased significantly with the increase of GNPs fillers, but decreased with the increase of temperature. Moreover, thermogravimetric analysis demonstrated that coupling GNPs resulted in better thermal stability of the WPCs. The limiting oxygen index test also showed that addition of GNPs caused good fire retardancy in WPCs. Incorporation of GNPs also led to an improvement in mechanical properties as compared to neat WPCs. Through a series of mechanical performance tests, it could be concluded that the flexural and tensile moduli of WPCs were improved with the increase of the content of fillers.

Synergistic Effects of Functional CNTs and h-BN on Enhanced Thermal Conductivity of Epoxy/Cyanate Matrix Composites

Epoxy/cyanate resin matrix composites (AG80/CE) with improved thermal conductivity and mechanical properties were obtained with synergetic enhancement with functional carbon nanotubes (f-CNTs) and hexagonal boron nitride (h-BN). AG80/CE performed as polymeric matrix and h-BN as conductivity filler which formed the main thermal conductivity channels. Small amounts of f-CNTs were introduced to repair defects in conductivity channels and networks. To confirm the synergetic enhancements, the thermal conductivity was investigated and analyzed with Agari’s model. Results indicated that with introduction of 0.5 wt% f-CNTs, the thermal conductivity coefficient (ƛ) increased to 0.745 W/mk, which is 1.38 times that of composites with just h-BN. Furthermore, the flexural strength and modulus of composites with 0.5 wt% f-CNTs were 85 MPa and 3.5 GPa. The glass transition temperature (T_g) of composites with 0.4 wt% was 285 °C and the initial decomposition temperature (T_5%) was 385 °C, indicating outstanding thermal stability. The obtained h-BN/f-CNTs reinforced AG80/CE composites present great potential for packaging continuous integration and miniaturization of microelectronic devices.

Enhanced thermal conductivity of epoxy composites filled with silicon carbide nanowires

In this study, we report a facile approach to fabricate epoxy composite incorporated with silicon carbide nanowires (SiC NWs). The thermal conductivity of epoxy/SiC NWs composites was thoroughly investigated. The thermal conductivity of epoxy/SiC NWs composites with 3.0 wt% filler reached 0.449 Wm^-1 K^-1, approximately a 106% enhancement as compared to neat epoxy. In contrast, the same mass fraction of silicon carbide micron particles (SiC MPs) incorporated into epoxy matrix showed less improvement on thermal conduction properties. This is attributed to the formation of effective heat conduction pathways among SiC NWs as well as a strong interaction between the nanowires and epoxy matrix. In addition, the thermal properties of epoxy/SiC NWs composites were also improved. These results demonstrate that we developed a novel approach to enhance the thermal conductivity of the polymer composites which meet the requirement for the rapid development of the electronic devices.

Reasons and remedies for the agglomeration of multilayered graphene and carbon nanotubes in polymers

One of the main issues in the production of polymer nanocomposites is the dispersion state of filler as multilayered graphene (MLG) and carbon nanotubes (CNTs) tend to agglomerate due to van der Waals forces. The agglomeration can be avoided by using organic solvents, selecting suitable dispersion and production methods, and functionalizing the fillers. Another proposed method is the use of hybrid fillers as synergistic effects can cause an improvement in the dispersion state of the fillers. In this review article, various aspects of each process that can help avoid filler agglomeration and improve dispersion state are discussed in detail. This review article would be helpful for both current and prospective researchers in the field of MLG- and CNT-based polymer nanocomposites to achieve maximum enhancement in mechanical, thermal, and electrical properties of produced polymer nanocomposites.

Mechanical, Thermal, and Electrical Properties of Graphene-Epoxy Nanocomposites-A Review

Monolithic epoxy, because of its brittleness, cannot prevent crack propagation and is vulnerable to fracture. However, it is well established that when reinforced—especially by nano-fillers, such as metallic oxides, clays, carbon nanotubes, and other carbonaceous materials—its ability to withstand crack propagation is propitiously improved. Among various nano-fillers, graphene has recently been employed as reinforcement in epoxy to enhance the fracture related properties of the produced epoxy–graphene nanocomposites. In this review, mechanical, thermal, and electrical properties of graphene reinforced epoxy nanocomposites will be correlated with the topographical features, morphology, weight fraction, dispersion state, and surface functionalization of graphene. The factors in which contrasting results were reported in the literature are highlighted, such as the influence of graphene on the mechanical properties of epoxy nanocomposites. Furthermore, the challenges to achieving the desired performance of polymer nanocomposites are also suggested throughout the article.

Formation of thermally conductive networks in isotactic polypropylene/hexagonal boron nitride composites via “Bridge Effect” of multi-wall carbon nanotubes and graphene nanoplatelets

Efficiently thermal conductive networks were fabricated in the iPP/h-BN composites by the “bridge effect” of MWCNTs or GNPs.

Use of graphene oxide in achieving high overall thermal properties of polymer for printed electronics

Superiority of ‘thick’ graphene oxide in simultaneously enhancing both the thermal conductivity and the dimensional and structural thermal stability of epoxy.