Thermal Conductivity of Polymer-Based Composites: Fundamentals and Applications

Review of thermal conductivity in composites: Mechanisms, parameters and theory

Homogeneous distribution of graphene flakes in a polymer matrix, still preserving intrinsic material properties, is key to successful composite applications. A novel approach is presented to disperse non-oxidized graphene flakes with non-covalent functionalization of 1-pyrenebutyric acid and to fabricate nanocomposites with outstanding thermal conductivity (∼1.53 W/mK) and mechanical properties (∼1.03 GPa).

Enhanced thermal conductivity of epoxy-graphene composites by using non-oxidized graphene flakes with non-covalent functionalization.

Polymers are widely used in industry and in our daily life because of their diverse functionality, light weight, low cost and excellent chemical stability. However, on some applications such as heat exchangers and electronic packaging, the low thermal conductivity of polymers is one of the major technological barriers. Enhancing the thermal conductivity of polymers is important for these applications and has become a very active research topic over the past two decades. In this review article, we aim to: 1). systematically summarize the molecular level understanding on the thermal transport mechanisms in polymers in terms of polymer morphology, chain structure and inter-chain coupling; 2). highlight the rationales in the recent efforts in enhancing the thermal conductivity of nanostructured polymers and polymer nanocomposites. Finally, we outline the main advances, challenges and outlooks for highly thermal-conductive polymer and polymer nanocomposites.

Thermal conductivity of polymers and polymer nanocomposites

Polymers are usually considered as thermal insulators, and their applications are limited by their low thermal conductivity. However, recent studies have shown that certain polymers have surprisingly high thermal conductivity, some of which are comparable to that in poor metals or even silicon. Here, the experimental achievements and theoretical progress of thermal transport in polymers and their nanocomposites are outlined. The open questions and challenges of existing theories are discussed. Special attention is given to the mechanism of thermal transport, the enhancement of thermal conductivity in polymer nanocomposites/fibers, and their potential application as thermal interface materials.

Thermal Conductivity of Polymers and Their Nanocomposites.

Improving thermal conductivity while retaining high electrical resistivity of epoxy composites by incorporating silica-coated multi-walled carbon nanotubes

Hyperbranched poly(urea-urethane)-grafted multi-walled carbon nanotubes (HPU-MWCNTs) were incorporated in a polyurethane (PU) matrix based on poly(ethylene oxide-tetrahydrofuran) and aliphatic polyisocyanate resin as curing agent. The 9–12 nm thick HPU shell formed on the MWCNTs improved the dispersion of MWCNTs and enhanced the interfacial adhesion between the PU matrix and MWCNTs, leading to improvements in storage modulus and Tg of the composites and enhancement of the thermal stability of PU. Thus, composites with 0.5–1 wt% MWCNTs increased the thermal conductivity by about 60–70% when compared to, and retained the high electrical resistivity of, neat PU.

Thermal conductive and electrical properties of polyurethane/hyperbranched poly(urea-urethane)-grafted multi-walled carbon nanotube composites

Silica coated multiwalled carbon nanotubes (SiO 2 @MWCNTs) with different coating thicknesses of ∼4 nm, 30–50 nm, and 70–90 nm were synthesized by a sol–gel method and compounded with polyurethane (PU). The effects of SiO 2 @MWCNTs on the electrical properties and thermal conductivity of the resulting PU/SiO 2 @MWCNT composites were investigated. The SiO 2 coating maintained the high electrical resistivity of pure PU. Meanwhile, incorporating 0.5, 0.75 and 1.0 wt% SiO 2 @MWCNT (70–90 nm) into PU, produced thermal conductivity values of 0.287, 0.289 and 0.310 W/mK, respectively, representing increases of 62.1%, 63.3% and 75.1%. The thermal conductivity of PU/SiO 2 @MWCNT composites was also increased by increasing the thickness of the SiO 2 coating.

Effect of silica coating thickness on the thermal conductivity of polyurethane/SiO2 coated multiwalled carbon nanotube composites

Effect of silica coating thickness on the thermal conductivity of polyurethane/SiO2 coated multiwalled carbon nanotube composites Part A Applied science and manufacturing

As a new coding standard, Versatile Video Coding (VVC) introduces the quad-tree plus multi-type tree (QTMT) partition structure, which significantly improves coding efficiency compared to High-Efficiency Video Coding (HEVC). The QTMT partition structure further enhances the flexibility of coding unit (CU) partitioning and improves the efficiency of VVC encoding high-resolution video, but introduces an unacceptable coding complexity at the same time. This paper proposes an SVM-based fast CU partition decision algorithm to reduce the coding complexity for VVC. First, the proportion of split modes with different CU sizes is analyzed to explore a method to effectively reduce coding complexity. Then, more reliable correlation features are selected based on the maximum ratio of the standard deviation (SD) and the edge point ratio (EPR) in sub-CUs. Finally, two SVM models are designed and trained using the selected features to provide guidance for deciding whether to divide and the direction of partition. The simulation results indicate that the proposed algorithm can save 54.05% coding time on average with 1.54% BDBR increase compared with VTM7.0.

/pdf/svm-based-fast-cu-partition-decision-algorithm-for-vvc-intra-3gq9fi9r.pdf

Jinchao Zhao

Papers

Improving thermal conductivity while retaining high electrical resistivity of epoxy composites by incorporating silica-coated multi-walled carbon nanotubes

Thermal conductive and electrical properties of polyurethane/hyperbranched poly(urea-urethane)-grafted multi-walled carbon nanotube composites

Effect of silica coating thickness on the thermal conductivity of polyurethane/SiO2 coated multiwalled carbon nanotube composites

Effect of silica coating thickness on the thermal conductivity of polyurethane/SiO2 coated multiwalled carbon nanotube composites Part A Applied science and manufacturing

SVM-Based Fast CU Partition Decision Algorithm for VVC Intra Coding