A comparative study of the thermal interface materials with graphene and boron nitride fillers

ACS Appl. Mater. Interfaces

Salgado

et al. 2018

268

230

We investigated thermal properties of the epoxy-based composites with a high loading fractionup to ≈ 45 vol. % -of the randomly oriented electrically conductive graphene fillers and electrically insulating boron nitride fillers. It was found that both types of the composites revealed a distinctive thermal percolation threshold at the loading fraction > 20 vol. %. The graphene loading required for achieving the thermal percolation, , was substantially higher than the loading, , for the electrical percolation. Graphene fillers outperformed boron nitride fillers in the thermal conductivity enhancement. It was established that thermal transport in composites with the high filler loading, ≥ , is dominated by heat conduction via the network of percolating fillers. Unexpectedly, we determined that the thermal transport properties of the high loading composites were influenced strongly by the cross-plane thermal conductivity of the quasi-twodimensional fillers. The obtained results shed light on the debated mechanism of the thermal × Contributed equally to the work. * Corresponding author (A.A.B.): balandin@ece.ucr.edu ; web-site: http://balandingroup.ucr.edu/ Thermal Percolation Threshold and Thermal Properties of Composites with Graphene and Boron Nitride Fillers, UCR (2018) 2 | P a g e percolation, and facilitate the development of the next generation of the efficient thermal interface materials for electronic applications. Main TextThe discovery of unique heat conduction properties of graphene 1-7 motivated numerous practically oriented studies of the use of graphene and few-layer graphene (FLG) in various composites, thermal interface materials and coatings [8][9][10][11][12][13][14][15] . The intrinsic thermal conductivity of large graphene layers exceeds that of the high-quality bulk graphite, which by itself is very high -2000 Wm −1 K −1 at room temperature (RT) 1,11,16,17 . The first studies of graphene composites found that even a small loading fractions of randomly oriented graphene fillers -up to = 10 vol. %can increase the thermal conductivity of epoxy composites by up to a factor of ×25 [Ref. 11]. These results have been independently confirmed by different research groups 18,19 . The variations in the reported thermal data for graphene composites can be explained by the differences in the methods of preparation, matrix materials, quality of graphene, lateral sizes and thickness of graphene fillers and other factors 3,20-25 . Most of the studies of thermal composites with graphene were limited to the relatively low loading fractions, ≤ 10 vol. %. The latter was due to difficulties in preparation of high-loading fraction composites with a uniform dispersion of graphene flakes. The changes in viscosity and graphene flake agglomeration complicated synthesis of the consistent set of samples with the loading substantially above = 10 vol. %.Investigation of thermal properties of composites with the high loading fraction of graphene or FLG fillers is interesting from both fundamental science and practical applicat...

Section: Main Textmentioning

confidence: 99%

mentioning

confidence: 99%

Thermal Percolation Threshold and Thermal Properties of Composites with High Loading of Graphene and Boron Nitride Fillers

Kargar

ACS Appl. Mater. Interfaces

Salgado

et al. 2018

268

230

“…The intrinsic thermal conductivity of graphene can exceed that of the high‐quality bulk graphite, which by itself is high—2000 W m −1 K −1 at RT . Numerous studies reported enhancement of the thermal properties of TIMs and various other composites as a result of incorporation of SLG and FLG . The first studies showed that adding even a small loading fraction of the optimized mixture of graphene and FLG (up to f = 10 vol%) to the pristine epoxy increases its thermal conductivity by a factor of ×25 .…”

Section: Introductionmentioning

confidence: 99%

Dual‐Functional Graphene Composites for Electromagnetic Shielding and Thermal Management

Kargar

Balinskiy

et al. 2018

Adv Elect Materials

196

132

and environment. [12][13][14] The current industrial and safety standards require blocking of more than 99% of the EM radiation from any electronic devices. [1,[15][16][17] From the other side, the operation of the electronic devices can be disrupted by the outside EM waves. The heat and EM radiation have an inherent connection-absorption of EM waves by any material results in its heating. The energy from EM wave transfers to electrons and then to phonons-quanta of crystal lattice vibrations. The conventional approach for handling the heat and EM radiation problems is based on utilization of the thermal interface materials (TIM), which can spread the heat, and electromagnetic interference (EMI) shielding materials, which can protect from EM waves. These two types of materials have different, and, often, opposite characteristics, e.g., excellent EMI material can be a poor heat conductor, while efficient TIM can utilize electrically nonconductive fillers, resulting in its transparency for EM waves. Here, we propose a concept of the "dual-functional" EMI shielding-TIM materials, and demonstrate it on the example of graphene composites.It is well known that EMI shielding requires interaction of the EM waves with the charge carriers inside the material so that EM radiation is reflected or absorbed. For this reason, the EMI shielding material must be electrically conductive or contain electrically conductive fillers, although a high electrical conductivity is not required. The bulk electrical resistivity on the order of 1 Ω cm is sufficient for most of EMI shielding applications. [1,3,15] Most of the polymer-based materials widely used as TIMs in electronic packaging are electrically insulating and, therefore, transmit EM waves. Conventionally, metal particles are added as fillers in high volume fractions to the base polymer matrix in order to increase the electrical conductivity and prevent EM wave propagation from the device to the environment and vice versa. [1,[18][19][20][21] However, the polymer-metal composites suffer from high weight, cost, and corrosion, which make them an undesirable choice for the state-of-the-art downscaled electronics. Several studies reported the use of carbon fibers, [22][23][24][25][26][27][28][29] carbon black, [30,31] bulk graphite, [32][33][34] carbon nanotubes (CNT), [16,17,[35][36][37][38][39] reduced graphene oxide (rGO), [2,6,[40][41][42][43][44][45][46][47][48][49][50] graphene, [51][52][53][54] and combination of carbon allotropes with orThe synthesis and characterization of epoxy-based composites with few-layer graphene fillers, which are capable of dual-functional applications, are reported. It is found that composites with certain types of few-layer graphene fillers reveal an efficient total electromagnetic interference shielding, SE tot ≈ 45 dB, in the important X-band frequency range, f = 8.2 −12.4 GHz, while simultaneously providing high thermal conductivity, K ≈ 8 W m −1 K −1 , which is a factor of ×35 larger than that of the base matrix material. The efficiency of the d...

“…Hexagonal boron nitride (h-BN) is a natural choice for use as a complementary, electrically insulating, filler with graphene [26,[28][29][30]. It is known that h-BN has a high intrinsic thermal conductivity [31][32][33].…”

Section: Introductionmentioning

confidence: 99%

Thermal and electrical conductivity control in hybrid composites with graphene and boron nitride fillers

Lewis

Magana

et al. 2019

Mater. Res. Express

113

We report on the thermal and electrical properties of hybrid epoxy composites with graphene and boron nitride fillers. The thicknesses, lateral dimensions, and aspect ratios of each filler material were intentionally selected for geometric similarity to one another, in contrast to prior studies that utilized dissimilar filler geometries to achieve a "synergistic" effect. We demonstrate that the electrically-conductive graphene and electrically-insulating boron nitride fillers allow one to effectively engineer the thermal and electrical conductivities of their resulting composites. By varying the constituent fraction of boron nitride to graphene in a composite with ~44% total filler loading, one can tune the thermal conductivity enhancement from a factor of ×15 to ×35 and increase the electrical conductivity by many orders of magnitude. The obtained results are important for the development of next-generation thermal interface materials with controllable electrical properties necessary for applications requiring either electrical grounding or insulation.