Abstract

The demand in adequate heat dissipation in electronic and electrical devices has enhanced the need for more efficient thermal interface materials (TIMs). For the synthesis of TIMs, a polymer matrix is filled with ceramic fillers which form a thermally conductive but electrically insulating network. Graphene is a promising material with exceptionally high thermal conductivity (TC) which makes graphene an excellent candidate for TIMs applications. The literature shows that the mechanical properties can influence TIMs’ application scope, however limited research has been carried out on the effect of graphene on different desirable properties of elastomeric materials when these are filled with high (>40 wt%) loadings of ceramic particles. This thesis aims to evaluate the effect of nanofiller and microfiller loading on the thermal, mechanical, and physical properties of silicone based TIMs. Polydimethylsiloxane was used as matrix and filled with single or binary combinations of the following untreated fillers: few-layer graphene (FLG) (≈7 layers, 1.32×0.9 μm lateral size), graphene nanoplatelets (GNPs) (≈14.5 layers, 2.16×1.78 μm lateral size) at a loading of up to 12 wt%, and ceramics at loadings of up to 80 wt% were dispersed through solution mixing using an overhead stirrer to produce elastomeric TIMs. The TC of samples increased with increase in filler loading, and it was shown that addition of graphene caused further increase in TC. Hexagonal boron nitride (hBN) platelets at 40 wt% loading exhibited better synergy with GNPs, producing formulations with TC of 1.23 W m-1 K-1. Aluminium oxide (Al2O3) and aluminium nitride (AlN) worked best when combined with FLG, achieving TC of 0.74 W m-1 K-1 and 1.26 W m-1 K-1 for samples filled with 5 wt% FLG and 60 wt% Al2O3 or AlN respectively. DSC revealed that graphene can reduce the ultimate heat of curing, shift peak of curing to higher temperatures and prevent curing. A drastic change in mechanical properties, especially for nanocomposites filled with GNPs was observed, and the effect was used to investigate the mechanical properties of different cured formulations. For example, when 8 wt% GNPs were added to samples filled with 40 wt% hBN, the elongation at break increased from 57.2% to 161.9%, while the tensile strength dropped from 1.8 MPa to 0.8 MPa. The softening effect of graphene on PDMS was also explored with Shore hardness tests. Rheology showed that FLG can cause a higher increase in viscosity than GNPs, limiting the loading of filler to be added in TIMs. TGA was performed to study the thermal stability and confirmed that addition of graphene in samples filled with ceramic fillers does not reduce the range of operational temperature. Scanning electron microscopy revealed good dispersion and confirmed the filler’s size. This research can aid in the production of formulations filled with graphene by providing insights to material properties and processing, which can directly influence the performance of TIMs.