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

Abstract

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).

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

“…This is due to the fact that the AgNWs, presenting relative higher intrinsic λ than that of BNNS, exert a more positive influence on the λ of composite films. [59] The direct mixing of AgNWs and BNNS is beneficial to the increment of the probability for the formation of thermal conduction pathways in ANF composite films, yet AgNWs and BNNS themselves are prone to agglomeration in the ANF matrix, and inevitably introduce additional thermal resistance at AgNWs-BNNS or AgNWs-ANF-BNNS interfaces. In contrast, in AgNWs@BNNS, AgNWs with high aspect ratio act as a "bridge" for carrying BNNS flakes, which can effectively avoid the introduction of more interfacial thermal resistance between AgNWs, BNNS, and ANF, the synergistic advantages of one-dimensional linear AgNWs and two-dimensional flake-like BNNS can be fully exploited, making it easier to form interpenetrating thermal conduction pathways in the ANF matrix, greatly reducing the phonon scattering and improving the phonon propagation efficiency, which in turn endows the AgNWs@BNNS/ANF composite films with optimal thermal conductivity.…”

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

“…During the heating process of LC-CNT, the 7CB on the surface shows the thermotropic liquid crystal transition, successively transforms from a solid-state crystal state to a liquid crystal state, and finally transforms to an isotropic liquid state (Figure S2c), indicating that 7CB still maintains the liquid crystal characteristics after being assembled on the surface of CNT. [44,45] Figure 2a, b present the POM images of CNT/ DMAc and LC-CNT/DMAc dispersions under the alternating electric field (in the horizontal direction, with frequency of 150 kHz and amplitude of 600 V, same as follows), respectively. When no alternating electric field was applied, the CNT/DMAc and LC-CNT/DMAc dispersions only show scattered black spots against the red background (Figure 2a 1 , Figure 2b 1 ).…”

Liquid Crystal Materials for Biomedical Applications

“…[168] Thus, for orderly arranged chains, the heat transfer could occur preferentially along the alignment direction, leading to efficient suppression of phonon scattering. [169] Recent studies have shown that the thermal conductivity of liquid crystals can be enhanced by several methods, including the addition of nanomaterials or by incorporating functional groups. [170][171][172][173][174] For example, the addition of carbon nanotubes to liquid crystal systems has been shown to significantly enhance their thermal conductivity, due to their high intrinsic thermal conductivity.…”