探討石墨烯/環氧樹脂奈米複合材料之機械與熱傳導特性

Abstract

本研究探討石墨烯及石墨烯/環氧樹脂奈米複合材料之機械與熱傳導特性。首先藉由分子動力學(molecular dynamics)模擬，探討表面改質對於石墨烯彈性常數及熱導率之影響，結果顯示改質石墨烯具較低之彈性常數及熱導率(thermal conductivity)。透過瞭解改質官能基對於石墨烯/環氧樹脂奈米複合材料熱導率之影響，包括界面熱傳導(interfacial thermal conductance)、聲子失配(phonon mismatch)及互動能量(normalized interaction energy)之變化，結果顯示官能基能夠增加界面互動及降低界面聲子失配，並進而提高界面熱傳導及鄰近環氧樹脂內的熱能傳遞。最後本研究以分子模擬結合微觀力學分析探討奈米複合材料楊氏模數及熱導率，其中奈米複合材料分別含有未改質石墨烯(pristine graphene)、羧基(carboxyl)改質石墨烯和羧基與胺基(amine)改質石墨烯。經由分子動力學模擬石墨烯及環氧樹脂間的界面互動，再以連續體之等效概念，獲得石墨烯之有效材料性質，並利用微觀力學模型來預估石墨烯奈米複合材料機械與熱傳導性質。分析結果顯示羧基與胺基改質之石墨烯奈米複合材料具較佳機械與熱傳導性質，此模擬分析結果與實驗量測相符。

The aim of this study is to characterize the mechanical properties and thermal conductivities of graphene/epoxy nanocomposites. The elastic constants and thermal conductivity were investigated for the pristine graphene and functionalized graphene through molecular dynamics (MD) simulations. The results indicated that implanting functional groups would reduce the in-plane Young’s modulus and thermal conductivity. Subsequently, the influences of functional groups grafted on the graphene surface on the properties of nanocomposites were explored by examining the interfacial thermal conductance (ITC), phonon mismatch, and normalized interaction energy. It was shown that functional groups could increase the interactions and decrease the phonon mismatch at the interface so that the ITC and thermal transport in the interfacial epoxy could be enhanced significantly. Afterward, the atomistic simulation together with micromechanical analysis was employed to characterize the Young’s modulus and thermal conductivity of graphene/epoxy nanocomposites. The atomistic interaction between graphene and the surrounding epoxy was considered in the molecular dynamic simulation and then used to derive the effective properties of graphene. Subsequently, the Young’s moduli and thermal conductivities of nanocomposites with randomly oriented graphene were modeled from the Mori–Tanaka micromechanical model. The nanocomposites containing pristine graphene, carboxyl (COOH)-functionalized graphene, and COOH- and amine (NH2)-functionalized graphene were considered in the simulation. The results indicated that the COOH- and NH2-functionalized graphene nanocomposite exhibited superior mechanical and thermal properties to those of the other two material systems. Moreover, the model predictions were in good agreement with the experimental data.