Effect of magnetic field treatment on effective thermal conductivity for polyimide‐based composite sheet using magnetite‐decorated hexagonal boron nitride

Abstract

The use of magnetic field treatment (MFT) was investigated to establish the appropriate temperature needed to enhance the out‐of‐plane effective thermal conductivity (k) of polyimide (PI)‐based composite sheets. Hexagonal boron nitride (hBN) surfaces were decorated with magnetite particles (Fe3O4@hBN) for use as fillers. The magnetite amount was adjusted to a Fe3O4/hBN weight ratio of 0.2 in most cases. When MFT was carried out at the temperature starting from 80, 90, and 100°C, the effective k was enhanced compared with the lack of MFT. On the other hand, the effective k was not enhanced by the use of MFT at the starting temperature of either 150 or 200°C. Moreover, the cross‐sectional scanning electron microscope images and X‐ray diffractometer analyses of the sheets prepared both with and without MFT were consistent with the results of the effective k measurements. Namely, the fillers inside the sheets moved and rotated under MFT at the starting temperature of 80, 90, and 100°C. On the other hand, for MFT starting from either 150 or 200°C, the fillers were restrained due to high viscosity of the composite solutions. The results of measurements of the breakdown voltages also implied the formation of filler paths inside the sheets.

Synergistic effects of boron nitride sheets and reduced graphene oxide on reinforcing the thermal conduction, SERS performance and thermal property of polyimide composite films

“…22 Among reinforcement fillers, hexagonal boron nitride (hBN) acts as a kind of promising fillers in the domain of thermal conductive composites owning to its excellent TC value (300 Wm À1 K À1 ), highly thermal stability and superb chemical stability. 23 Graphene perform well in enhancing the TC values of composites synergistically because graphene presents an ultrahigh TC value ($5000 Wm À1 K À1 ). 24,25 Large amount of research have been done on preparing GO/PI films with high performance properties.…”

“…As reported previously, Hu et al introduced hybrid fillers of BN‐OH and dopamine functionalized AlN into PI matrix, obtaining hBN/AlN/PI composite whose TC values reached 1.01 Wm −1 K −1 at the filler loading of 25 wt% 22 . Among reinforcement fillers, hexagonal boron nitride (hBN) acts as a kind of promising fillers in the domain of thermal conductive composites owning to its excellent TC value (300 Wm −1 K −1 ), highly thermal stability and superb chemical stability 23 . Graphene perform well in enhancing the TC values of composites synergistically because graphene presents an ultrahigh TC value (~5000 Wm −1 K −1 ) 24,25 .…”

Enhancement of the effective thermal conductivity of iron oxide‐coated hexagonal boron nitride/polyimide composite sheets using samarium–cobalt magnets

“…Fe 3 O 4 @hBN was fabricated based using a method reported by Kim and Kim, 26 which we had used in a previous study. 33 hBN powder was first soaked in a 5 mol L À1 NaOH solution and stirred using a magnetic stirrer bar at 120 C for 48 h for surface modification with hydroxy groups. After washing with distilled water and drying, Fe 3 O 4 nanoparticles were produced on the hBN surface via hydrolysis method.…”

“…The MFT for the preparation of the composite sheets was performed during the drying process in a vacuum oven after step (2) described in Section 2.3. The MFT apparatus used in this study has been previously described, 33 and is schematized in Figure 1. The precursor on the glass plate was sandwiched between a pair of samarium-cobalt magnets (SS0040, Magfine Co.; 30 mm  30 mm  10 mm; surface magnetic flux density: 271 mT; residual magnetic flux density: 1030-1080 mT).…”

“…The appropriate temperature for MFT to increase the TC of the sheet was investigated. The distribution and orientation of the fillers inside the sheets drastically changed, and the TC of the composite sheets improved in the out-of-plane direction by performing MFT at <100 C. 33 Still, the strength of the magnetic field should also considered in MFT. In this study, we investigated the effect of magnetic field strength and of the force acting on the fillers, which were controlled by varying the relative position of the magnets and the sample during MFT, on the material properties of Fe 3 O 4 @hBN/ PI composite sheets.…”