Performance of Thermal Interface Materials

Low thermal contact resistance boron nitride nanosheets composites enabled by interfacial arc-like phonon bridge

Two-dimensional materials with ultrahigh in-plane thermal conductivity are ideal for heat spreader applications but cause significant thermal contact resistance in complex interfaces, limiting their use as thermal interface materials. In this study, we present an interfacial phonon bridge strategy to reduce the thermal contact resistance of boron nitride nanosheets-based composites. By using a low-molecular-weight polymer, we are able to manipulate the alignment of boron nitride nanosheets through sequential stacking and cutting, ultimately achieving flexible thin films with a layer of arc-like structure superimposed on perpendicularly aligned ones. Our results suggest that arc-like structure can act as a phonon bridge to lower the contact resistance by 70% through reducing phonon back-reflection and enhancing phonon coupling efficiency at the boundary. The resulting composites exhibit ultralow thermal contact resistance of 0.059 in2 KW-1, demonstrating effective cooling of fast-charging batteries at a thickness 2-5 times thinner than commercial products.

Alveoli-Mimetic Synergistic Liquid and Solid Thermal Conductive Interface as a Novel Strategy for Designing High-Performance Thermal Interface Materials

Thermal interface materials (TIMs) are in desperate desire with the development of the modern electronic industry. An excellent TIM needs desired comprehensive properties including but not limited to high thermal conductivity, low Yong's modulus, lightweight, as well as low price. However, as is typically the case, those properties are naturally contradictory. To tackle such dilemmas, a strategy of construction high-performance TIM inspired by alveoli is proposed. The material design includes the self-alignment of graphite into 3D interconnected thermally conductive networks by polydimethylsiloxane beads (PBs) -the alveoli; and a small amount of liquid metal (LM) - capillary networks bridging the PBs and graphite network. Through the delicate structural regulation and the synergistic effect of the LM and solid graphite filler, superb thermal conductivity (9.98 ± 0.34 W m-1 K-1) can be achieved. The light emitting diode (LED) application and their performance in the central processing unit (CPU) heat dispersion manifest the TIM developed in the work has stable thermal conductivity for long-term applications. The thermally conductive, soft, and lightweight composites are believed to be high-performance silicone bases TIMs for advanced electronics.

Fillers and methods to improve the effective (out-plane) thermal conductivity of polymeric thermal interface materials - A review

The internet of things and growing demand for smaller and more advanced devices has created the problem of high heat production in electronic equipment, which greatly reduces the work performance and life of the electronic instruments. Thermal interface material (TIM) is placed in between heat generating micro-chip and the heat dissipater to conduct all the produced heat to the heat sink. The development of suitable TIM with excellent thermal conductivity (TC) in both in-plane and through-plane directions is a very important need at present. For efficient thermal management, polymer composites are potential candidates. But in general, their thermal conductivity is low compared to that of metals. The filler integration into the polymer matrix is one of the two approaches used to increase the thermal conductivity of polymer composites and is also easy to scale up for industrial production. Another way to achieve this is to change the structure of polymer chains, which fall out of the scope of this work. In this review, considering the first approach, the authors have summarized recent developments in many types of fillers with different scenarios by providing multiple cases with successful strategies to improve through-plane thermal conductivity (TPTC) (k⊥). For a better understanding of TC, a comprehensive background is presented. Several methods to improve the effective (out-plane) thermal conductivity of polymer composites and different theoretical models for the calculation of TC are also discussed. In the end, it is given a detailed conclusion that provides drawbacks of some fillers, multiple significant routes recommended by other researchers to build thermally conductive polymer composites, future aspects along with direction so that the researchers can get a guideline to design an effective polymer-based thermal interface material.

Application-Driven High-Thermal-Conductivity Polymer Nanocomposites

Polymer nanocomposites combine the merits of polymer matrices and the unusual effects of nanoscale reinforcements and have been recognized as important members of the material family. Being a fundamental material property, thermal conductivity directly affects the molding and processing of materials as well as the design and performance of devices and systems. Polymer nanocomposites have been used in numerous industrial fields; thus, high demands are placed on the thermal conductivity feature of polymer nanocomposites. In this Perspective, we first provide roadmaps for the development of polymer nanocomposites with isotropic, in-plane, and through-plane high thermal conductivities, demonstrating the great effect of nanoscale reinforcements on thermal conductivity enhancement of polymer nanocomposites. Then the significance of the thermal conductivity of polymer nanocomposites in different application fields, including wearable electronics, thermal interface materials, battery thermal management, dielectric capacitors, electrical equipment, solar thermal energy storage, biomedical applications, carbon dioxide capture, and radiative cooling, are highlighted. In future research, we should continue to focus on methods that can further improve the thermal conductivity of polymer nanocomposites. On the other hand, we should pay more attention to the synergistic improvement of the thermal conductivity and other properties of polymer nanocomposites. Emerging polymer nanocomposites with high thermal conductivity should be based on application-oriented research.

Scalable microfluidic fabrication of vertically aligned two-dimensional nanosheets for superior thermal management

Two-dimensional (2D) nanosheets have been assembled into various macroscopic structures for wide engineering applications. To fully explore their exceptional thermal, mechanical, and electrical properties, 2D nanosheets must be aligned into highly ordered structures due to their strong structural anisotropy. Structures stacked layer by layer such as films and fibers have been readily assembled from 2D nanosheets due to their planar geometry. However, scalable manufacturing of macroscopic structures with vertically aligned 2D nanosheets remains challenging, given their large lateral size with a thickness of only a few nanometers. Herein, we report a scalable and efficient microfluidics-enabled sheet-aligning process to assemble 2D nanosheets into a large-area film with a highly ordered vertical alignment. By applying microchannels with a high aspect ratio, 2D nanosheets were well aligned vertically under strong channel size confinement and high flow shear stress. A vertically aligned graphene sheet film was obtained and applied to effectively improve the heat transfer of thermal interfacial materials (TIMs). Superior through-plane thermal conductivity of 82.7 W m-1 K-1 at a low graphene content of 11.8 vol% was measured for vertically aligned TIMs. Thus, they demonstrate exceptional thermal management performance for switching power supplies with high reliability.

Thermal Interface Materials with High Thermal Conductivity and Low Young's Modulus Using a Solid-Liquid Metal Codoping Strategy

Thermal interface materials (TIMs), as typical thermal functional materials, are highly required to possess both high thermal conductivity and low Young's modulus. However, the naturally synchronized change in the thermal and mechanical properties seriously hinders the development of high-performance TIMs. To tackle such a dilemma, a strategy of codoping solid fillers and liquid metal fillers into polymer substrates is proposed in this study. This strategy includes a large amount of liquid metals that play the role of thermal paths and a small amount of uniformly dispersed solid fillers that further enhance heat conduction. Through the synergistic effect of the liquid metal and solid fillers, the thermal conductivity can be improved, and Young's modulus can be kept small simultaneously. A typical TIM with a volume of 55% gallium-based liquid metal and 15% copper particles as fillers has a thermal conductivity of 3.94 W/(m·K) and a Young's modulus of 699 kPa, which had the maximum thermomechanical performance coefficient compared with liquid metal TIMs and solid filler-doped TIMs. In addition, the thermal conductivity of the solid-liquid metal codoped TIM increased sharply with an increase of liquid metal content, and Young's modulus increased rapidly with an increase of the volume ratio of copper and polymer. The high-low-temperature cycling test and large-size light-emitting diode (LED) application demonstrated that this TIM had stable physical performance. The synergistic effect of the solid fillers and liquid metal fillers provides a broad space to solve the classic tradeoff issue of the mechanical and thermal properties of composites.

Reducing interfacial thermal resistance by interlayer

Heat dissipation is crucial important for the performance and lifetime for highly integrated electronics, Li-ion battery-based devices and so on, which lies in the decrease of interfacial thermal resistance (ITR). To achieve this goal, introducing interlayer is the most widely used strategy in industry, which has attracted tremendous attention from researchers. In this review, we focus on bonding effect and bridging effect to illustrate how introduced interlayer decreases ITR. The behind mechanisms and theoretical understanding of these two effects are clearly illustrated. Simulative and experimental studies toward utilizing these two effects to decrease ITR of real materials and practical systems are reviewed. Specifically, the mechanisms and design rules for the newly emerged graded interlayers are discussed. The optimization of interlayers by machine learning algorithms are reviewed. Based on present researches, challenges and possible future directions about this topic are discussed.

AWI-Assembled TPU-BNNS Composite Films with High In-Plane Thermal Conductivity for Thermal Management of Flexible Electronics

Thermal management of flexible/stretchable electronics has been a crucial issue. Mass supernumerary thermal heat is created in the repetitive course of deformation because of the large nanocontact resistance between electric conductive fillers, as well as the interfacial resistance between fillers and the polymer matrix. Here, we report a stretchable thermoplastic polyurethane (TPU)-boron nitride nanosheet (BNNS) composite film with a high in-plane thermal conductivity based on an air/water interfacial (AWI) assembly method. In addition to rigid devices, it was capable for thermal management of flexible electronics. During more than 2000 cycles of the bending-releasing process, the average saturated surface temperature of the flexible conductor covered with composite film with 30 wt % BNNSs was approximately 40.8 ± 1 °C (10.5 °C lower than that with pure TPU). Moreover, the thermal dissipating property of the composite under stretching was measured. All the results prove that this TPU-BNNS composite film is a candidate for thermal management of next-generation flexible/stretchable electronics with high power density.