Large Enhancement in Thermal Conductivity of Solvent−Cast Expanded Graphite/Polyetherimide Composites

Abstract

We demonstrate in this work that expanded graphite (EG) can lead to a very large enhancement in thermal conductivity of polyetherimide−graphene and epoxy−graphene nanocomposites prepared via solvent casting technique. A k value of 6.6 W⋅m−1⋅K−1 is achieved for 10 wt% composition sample, representing an enhancement of ~2770% over pristine polyetherimide (k~0.23 W⋅m−1⋅K−1). This extraordinary enhancement in thermal conductivity is shown to be due to a network of continuous graphene sheets over long−length scales, resulting in low thermal contact resistance at bends/turns due to the graphene sheets being covalently bonded at such junctions. Solvent casting offers the advantage of preserving the porous structure of expanded graphite in the composite, resulting in the above highly thermally conductive interpenetrating network of graphene and polymer. Solvent casting also does not break down the expanded graphite particles due to minimal forces involved, allowing for efficient heat transfer over long−length scales, further enhancing overall composite thermal conductivity. Comparisons with a recently introduced effective medium model show a very high value of predicted particle–particle interfacial conductance, providing evidence for efficient interfacial thermal transport in expanded graphite composites. Field emission environmental scanning electron microscopy (FE−ESEM) is used to provide a detailed understanding of the interpenetrating graphene−polymer structure in the expanded graphite composite. These results open up novel avenues for achieving high thermal conductivity polymer composites.

Role of four-phonon processes in thermal conductivity of two-dimensional materials and thermal-transport enhancement arising from interconnected nanofiller networks in polymer/nanofiller composites

“…The composite also showed an electrical conductivity of 969 S m −1 . For the same filler concentration, Tarannum et al 104 demonstrated that the polyetherimide/EG composite exhibited 900% higher thermal conductivity (10 W m −1 K −1 ) than the polyetherimide/ graphene composite following a solvent casting process.…”

The Influence of Machining Conditions on the Orientation of Nanocrystallites and Anisotropy of Physical and Mechanical Properties of Flexible Graphite Foils

“…With an increase in density, the number of contacts between graphite packs increases, which leads to a regular decrease in the porosity of the material and better adhesion of particles to each other [ 34 , 35 ]. This leads to an increase in the electrical and heat-conducting properties of the material [ 36 , 37 , 38 , 39 , 40 ], while its gas permeability decreases [ 19 , 27 , 41 , 42 ].…”

A systematic molecular dynamics study of the thermal conductivities of polyetherimide/graphene nanocomposites using response surface methodology

“…3,4 In general, adding conductive nanofillers to a polymer matrix is a versatile approach to improve its thermal conductivity. 5,6 Researchers have attempted to improve the thermal conductivity of PI or PEI by adding various pure or hybrid nanofillers, such as carbon nanofibers, 7 aluminum nitride (AlN), 8 low-melting-point SnBi 17 Cu 0.5 , 9 hybrid carbon nanotube (CNT)/PI-grafted multiwall CNT/AlN, 10 PI-coated hexagonal boron nitride (h-BN), 11,12 iron oxide-doped h-BN, 12 expanded graphite, 13 short fiber/expanded graphite, 14 alkyl-or phenyl-aminated graphene oxide (GO), 15,16 graphite nanoplatelets, 17 and graphene nanoplatelets (GNPs) 18 to the polymer matrix. Among these, GNPs and their derivatives or hybrids are versatile nanofillers that have also been used to improve the thermal conductivity of other polymer matrices.…”