Effect of the in-plane aspect ratio of a graphene filler on anisotropic heat conduction in paraffin/graphene composites.

Hiroki Matsubara,Taku Ohara

doi:10.1039/d1cp00556a

Abstract

Enhancement of polymer thermal conductivity using nanographene fillers and clarification of its molecular-scale mechanisms are of great concern in the development of advanced thermal management materials. In the present study, molecular dynamics simulation was employed to theoretically show that the in-plane aspect ratio of a graphene filler can have a significant impact on the effective thermal conductivity of paraffin/graphene composites. Our simulation included multiple graphene fillers aggregated in a paraffin matrix. The effective thermal conductivity of a paraffin/graphene composite, described as a second-rank tensor in the framework of equilibrium molecular dynamics simulation, was calculated for two types of graphene fillers with the same surface area but in-plane aspect ratios of 1 and 10. The filler with the higher aspect ratio was found to exhibit a much higher thermal conductivity enhancement than the one with the lower aspect ratio. This is because a high in-plane aspect ratio strongly restricts the orientation of fillers when they aggregate and, consequently, highly ordered agglomerates are formed. On decomposing the effective thermal conductivity tensor into various molecular-scale contributions, it was identified that the thermal conductivity enhancement is due to the increased amount of heat transfer inside the graphene filler, particularly along the longer in-plane axis. The present result indicates a possibility of designing the heat conduction characteristics of a nanocomposite by customizing the filler shapes so as to control the aggregation structure of the fillers.

Highlights

Composites consisting of a paraffin matrix and graphene fillers have attracted interest as thermal materials, such as phase change materials (PCMs) for thermal energy storage[1] and thermal interface materials (TIMs) for reducing thermal resistance in semiconductor devices.[2]
The curve was approximately constant after t = 8 ps, and the steady-state value of the principal thermal conductivity was determined as the time average over t = 8–10 ps
Our results clearly indicate that an increased amount of heat transfer inside the graphene fillers is the dominant factor for thermal conductivity enhancement upon adding graphene fillers

Summary

Introduction

Composites consisting of a paraffin matrix and graphene fillers have attracted interest as thermal materials, such as phase change materials (PCMs) for thermal energy storage[1] and thermal interface materials (TIMs) for reducing thermal resistance in semiconductor devices.[2] While paraffin has many advantages including light weight, high flexibility, and low cost, it has the disadvantage of a low thermal conductivity, of the order of 10À1 W (m K)À1. Graphene, whose thermal conductivity has been reported to be in the range of 1000–5000 W (m K)À1,3,4 is a suitable filler to enhance the thermal conductivity of paraffin. Attempts have been made to use various types of nanographene fillers.[5,6] The observed values for the effective thermal conductivity of actual paraffin/graphene composites are rather scattered in the range

Methods

Results

Conclusion