Significant enhancement of thermal conductivity in graphite/polyester composite via interfacial π–π interaction

Abstract

Interfacial thermal resistance between matrix and filler is one of the most serious factors hindering heat transfer in composites. Here, a type of liquid crystalline polyester (LCP) containing phenyl pendant groups was intended to blend with pristine graphite by interfacial interaction. The intensity at 26.6° of the wide angle X‐ray diffraction pattern which exceeded that of pristine graphite indicated the existence of a strong interfacial π–π interaction. Both DSC and XRD tests showed that the ordered structure of the LCP matrix is directly affected by the mass fraction of graphite, indicating the interfacial interaction between LCP and graphite. By increasing the content of graphite, the thermal diffusivity showed a sharp increment by 1004%. The maximum thermal conductivity of the composite reached 28.613 W m−1 K−1, which was seven times that of traditional thermoplastic blended with graphite. Compared with the data calculated using effective medium theory, interfacial interaction plays a significant role in enhancing the thermal conductivity of the composites. Furthermore, the maximum tensile strength of this series of composites reached 13.3 MPa and the maximum Young's modulus reached 1067 MPa, exhibiting a potential guideline for further applications in flexible electronics. © 2019 Society of Chemical Industry

Enhancing intrinsic thermal conductivities of epoxy resins by introducing biphenyl mesogen-containing liquid crystalline co-curing agents

“…The interplanar spacings, calculated according to the Bragg formula, 43,44 are: 3.39, 1.87, 0.464, 0.432, 0.371, and 0.302 nm for LCER1; 2.85, 1.42, 0.474, 0.433, 0.377, and 0.308 nm for LCER2; and 2.91, 1.43, 0.473, 0.435, 0.378, and 0.309 nm for LCER3. Meanwhile, the respective diffraction peaks at 2 θ = 29.55°, 28.93°, and 28.89° for LCER1, LCER2, and LCER3 indicate the formation of π–π stacking, 45 which proves the presence of ordered interlayer structures. In addition, the sharp diffraction peaks at 2 θ between 2 and 10° reveal the formation of a smectic layer.…”

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

“…The corresponding intermolecular packing model is shown in Figure 3(e). In addition, the sharp diffraction peak at 2θ = 27:1 °implies the formation of π-π stacking structure [46] (Figure 3(f)), because ester group makes contiguous benzene rings shift and offset to form "sidestep" structure, which is conducive to the formation of intermolecular π-π stacking. As temperature further decreases, crystalline state is formed, while previous sharp diffraction peaks are still present, indicating that the ordered structures formed in liquid crystal state are fixed during crystallization process.…”

“…But their intrinsic λ values are still low (e.g., the λ of Vectra A950 type liquid crystal polyester is only 0.22 W/(m•K)) [42], and a large number of rigid structures in molecular chains inevitably raises the phase transition temperature, which is unfavorable for molding and processing [43][44][45]. Recently, researchers have devoted themselves to optimizing molecular structures of liquid crystal polyesters to decrease phase transition temperature, and simultaneously to enhance the orderliness of molecular structures in the hope of maximizing intrinsic λ of liquid crystal polyesters [46][47][48]. Wu et al [49] prepared several biphenyl-type polyesters, which contain flexible methylene units with different length, using BP, phenylsuccinic acid, 3-chloro-1-propanol, 6-chloro-1hexanol, and 9-bromo-1-nonanol by melt polycondensation.…”