Anisotropic Thermal Diffusivity of Hexagonal Boron Nitride-Filled Polyimide Films: Effects of Filler Particle Size, Aggregation, Orientation, and Polymer Chain Rigidity

Abstract

A series of inorganic/organic composite films exhibiting high thermal stability and high thermal diffusivity was prepared from five different grades of flake-shaped hexagonal boron nitride (hBN) and aromatic polyimides (PIs). Thermal diffusivities along the out-of-plane (D(perpendicular)) and in-plane (D//) directions of hBN/PI films were separately measured and analyzed in terms of particle size, shape, concentration, and orientation, as well as molecular structures of rigid and flexible PI matrices. hBN/PI films filled with large flake-shaped particles exhibited a large anisotropy in D(perpendicular) and D// due to the strong in-plane orientation of heat-conducting basal plane of hBN, while smaller anisotropy was observed in composites with small flakes and aggregates which tend to orient less in the in-plane direction during film processing. The anisotropic thermal diffusion property observed in hBN/PI films exhibited strong correlation with the orientation of hBN particles estimated using scanning electron micrographs (SEM) and wide-angle X-ray diffraction. Moreover, composites of hBN with a rigid-rod PI matrix exhibited much larger anisotropy in D(perpendicular) and D// than flexible PI-composites, reflecting the effect of the rigid and densely packed PI chains preferentially orienting parallel to the film plane. The thermal conductivities of the hBN/rigid-rod PI films were estimated as 5.4 and 17.5 W/m·K along the out-of-plane and in-plane directions, respectively, which is one of the largest values ever reported.

A review on the role of interface in mechanical, thermal, and electrical properties of polymer composites

“…Therefore, the interfacial zones predominantly affect the thermal conductivity of the composite [245,246]. As a result, anything that can affect the interfacial regions (e.g., geometry of particles [247][248][249][250][251][252][253], aggregation [254][255][256], interfacial pressure [257], roughness [258][259][260], and the strength of interactions at the interfaces [261][262][263][264][265]) in the composites would influence their thermal conductivity. In this section, we will review the parameters affecting the interfacial interactions and their subsequent impact on the thermal conductivity of the composites.…”

Enhanced Thermal Conductivity in Polyimide/Silver Particle Composite Films Based on Spontaneous Formation of Thermal Conductive Paths

“…Values of ρ and C p for the composited films were estimated by the rule of mixture (ROM) [8]. Cross-sectional scanning electron microscope (SEM) images of the films were observed using a table-top electron microscope (Hitachi, TM-3000).…”

Percolation effect on thermal conductivity of filler-dispersed polymer composites

“…An increased volume content of the filler results in increased thermal conductivity but decreased dielectric strength of polymer composites (Li et al, 2007). The effective thermal conductivity of composites is affected by several factors: the thermal conductivities of the filler and polymer as well as the shape, volume content ratio, arrangement, and orientation angle of the filler (Wang et al, 2013 andTanimoto et al, 2013). Therefore, it is important to correctly predict the effective thermal conductivity from a thermal and dielectric management viewpoint.…”