Effect of electrical field treatment on thermal conductivity and mechanical strength of carbon nanofiber/polymer composite sheets with high filler content

Abstract

Electrical field treatment (EFT) using alternating current was investigated for the possibility that it could enhance the out-of-plane effective thermal conductivity (TC) of carbon nanofiber (CNF)/polymer composite sheets with high concentrations of filler. Two types of polymers were used as the base: fluorinated polyimide (PI) and silicone rubber. For the CNF/fluorinated PI, the influence of frequency was clarified at 2 kV of amplitude voltage when using a CNF concentration up to 15.0 vol%. As a result, the effective TC was clearly increased by EFT, and the degree of the enhancement of effective TC was obviously greater at 0.01 Hz than at either 100 or 1 Â 10 6 Hz. Moreover, the effective TCs of two types of CNF/silicone rubber were also enhanced by EFT with 2 kV and 0.01 Hz for concentrations of CNF up to 5.2 vol%, although there is a large difference in the preparation methods between CNF/fluorinated PI and CNF/silicone rubber. Furthermore, the tensile strength of the sheets prepared with EFT implied a change in the orientational structure of CNF inside the silicone rubber matrix, although the effect of EFT on the tensile strength was smaller compared with that on the effective TC.

Temperature dependency of electric field treatment for improvement of effective thermal conductivity of functional carbon/silicone rubber composite sheets

“…As for the composite sheet with EFT, a static‐type AC voltage‐induced apparatus was used, similar to previous work 13 . A schematic diagram for EFT equipment is shown in Figure 2.…”

“…In our previous study, the impact of EFT on the effective TC, in the out‐of‐plane direction of polyimide with fluorine groups and silicone rubber sheets including CNFs was investigated at a high content of CNF. An enhancement in the effective TC was observed for both composite sheets 13 . In EFT, curing behavior is one of the most important issues because the mobility of fillers is a significant factor governing the smooth formation of thermally conductive paths.…”

“…As for the composite sheet with EFT, a static-type AC voltage-induced apparatus was used, similar to previous work. 13 A schematic diagram for EFT equipment is shown in Figure 2. The EFT equipment is composed of a pair of electrodes and heaters that are in an acrylic box surrounded by heat insulator, a voltage amplifier (HJOPS-2B10; voltage window: À2 to +2 kV; Matsusada Precision Co.), and a function generator (eK-FGJ, Matsusada Precision Co.).…”

“…The effective TC in the out-of-plane direction of the cured sheets was measured using a TC meter built in-house on the basis of a temperature gradient steady-state method, and details on measurement and estimation methods of the effective TC was shown in the previous work. [13][14][15] The rheological properties of the pristine uncured silicone rubber and CNF/uncured silicone rubber composite solutions were measured using a rheometer (MCR702, Anton Paar Co.). A disposable parallel plate with a diameter of 25 mm was used, and the frequency was set at 10 Hz for all measurements.…”

“…An enhancement in the effective TC was observed for both composite sheets. 13 In EFT, curing behavior is one of the most important issues because the mobility of fillers is a significant factor governing the smooth formation of thermally conductive paths. Rheological properties are strongly related to curing behavior and filler mobility.…”