Thermal Conductivity of Polyamide-6,6/Carbon Nanotube Composites: Effects of Tube Diameter and Polymer Linkage between Tubes

Abstract

Reverse nonequilibrium molecular dynamics simulations were done to quantify the effect of the inclusion of carbon nanotubes (CNTs) in the Polyamide-6,6 matrix on the enhancement in the thermal conductivity of polymer. Two types of systems were simulated; systems in which polymer chains were in contact with a single CNT, and those in which polymer chains were in contact with four CNTs, linked together via polymer linkers at different linkage fractions. In both cases, heat transfer in both perpendicular and parallel (to the CNT axis) directions were studied. To examine the effect of surface curvature (area) on the heat transfer between CNT and polymer, systems containing CNTs of various diameters were simulated. We found a large interfacial thermal resistance at the CNT-polymer boundary. The interfacial thermal resistance depends on the surface area of the CNT (lower resistances were seen at the interface of flatter CNTs) and is reduced by linking CNTs together via polymer chains, with the magnitude of the reduction depending on the linkage fraction. The thermal conductivity of polymer in the perpendicular direction depends on the surface proximity; it is lower at closer distances to the CNT surface and converges to the bulk value at distances as large as 2 nm. The chains at the interface of CNT conduct heat more in the parallel than in the perpendicular directions. The magnitude of this thermal conductivity anisotropy reduces with decreasing the CNT diameter and increasing the linkage fraction. Finally, microscopic parameters obtained from simulations were used to investigate macroscopic thermal conductivities of polymer nanocomposites within the framework of effective medium approximation.

Simulation of Percolation Threshold, Tunneling Distance, and Conductivity for Carbon Nanotube (CNT)-Reinforced Nanocomposites Assuming Effective CNT Concentration

“…Polymer carbon nanotubes (CNTs) nanocomposites (PCNT) are very attractive from research and application points of view, because they can elucidate important properties when the concentration of nanoparticles reaches the percolation threshold, which is the minimum CNT content that produces the conductive networks in nanocomposites [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15]. Long and thin CNTs normally introduce a low percolation threshold, producing a conductive nanocomposite by incorporation of very low CNT content [16].…”

Interfacial characteristics of a carbon nanotube-polyimide nanocomposite by molecular dynamics simulation

“…Molecular dynamics (MD) simulations have been utilized to investigate CNT/polymer interactions, and are an effective approach because they can eludicate molecularlevel details that are challenging to do experimentally. In previous work [18][19][20], the interactions between CNTs and polymers with different CNT diameter, chirality, orientation, chain rigidity, chain length and functional groups were predicted with MD simulations [21][22][23]. MD simulations were also used to predict the degree of structural ordering within the polymer matrix, specifically the alignment of the chains parallel to the CNT axis, thus impacting the mechanical modulus of the material but not large scale ordering within the bulk [24].…”

Study on the Effects of the Interphase Region on the Network Properties in Polymer Carbon Nanotube Nanocomposites

“…Many researchers have focused on polymer/carbon nanotubes (CNT) nanocomposites because their very low volume fractions show effective mechanical, thermal and chemical properties by preserving low density, transparency and simple processing [1][2][3][4][5][6][7][8][9][10]. The addition of CNT or graphene to polymers forms conductive nanocomposites, which has produced scientific interest in the research communities due to their potential applications in different fields, such as electronics and sensors [11][12][13][14][15][16][17][18][19][20][21][22][23][24][25].…”