Molecular dynamics modelling and simulations on graphene-polymer nanocomposites

Abstract

Fast growing power densities of modern electronic devices demand high-performance thermal interface materials (TIMs). Owing to a superior thermal conductivity of graphene, composites with graphene fillers dispersed in polymer matrix are expected to be promising TIM candidates. However, the thermal conductivity of graphene-polymer composites is hindered by a high thermal resistance across the interfaces between graphene fillers and polymer matrix. The research in this thesis is concerned with reducing the thermal transport across the graphene-polymer interfaces by employing a variety of treatment methods. Using molecular dynamics (MD) simulations, the effectiveness of covalent functionalisation, non-covalent functionalisation, dopants, defects and acetylenic linkages in reducing the graphene-polymer interfacial thermal resistance is investigated systematically. It is found that the covalent and non-covalent functionalisation techniques could considerably reduce the graphene-polymer interfacial thermal resistance. Among the various covalent functional groups, butyl is more effective than the others (i.e., carboxyl, hydroxyl and amines) in reducing the interfacial thermal resistance. Different non-covalent functional molecules, including 1-pyrenebutyl, 1-pyrenebutyric acid and 1-pyrenebutylamine, yield a similar amount of reduction. Moreover, it is found that the graphene-polymer interfacial thermal resistance is insensitive to defecting and doping in graphene, while it can be reduced moderately by replacing the sp2 bonds in graphene with acetylenic linkages. Using the effective medium theory, it is demonstrated that the overall thermal conductivity of graphene-polymer nanocomposites can be increased while the interfacial thermal resistance is reduced. The mechanical properties (i.e., Young's modulus and tensile strength) of the graphene-polymer nanocomposites are not affected by the noncovalent functionalisation technique, while they can be deteriorated by the covalent functionalisation of graphene. Based on the pull-out simulation results, it can be found that the interfacial shear stress between graphene and polymer is increased by the covalent functionalisation of graphene, while it is insensitive to the non-covalent functionalisation techniques.

Date of Award	2016
Original language	English