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

Kargar, Fariborz; Barani, Zahra; Salgado, Ruben; Debnath, Bishwajit; Lewis, Jacob; Aytan, Ece; Lake, Roger K.; Balandin, Alexander A.

doi:10.1021/acsami.8b16616

Cited by 256 publications

(243 citation statements)

References 83 publications

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“…At the low graphene loading fraction, f g = 5 wt%, graphene fillers are dispersed randomly in the polymer matrix and are separated apart, not forming a percolated network. Addition of the Cu‐NP fillers increases the thermal conductivity slightly as expected from the effective medium considerations . At a large loading of Cu‐NP, f Cu ≈ 40 wt%, the Cu‐NPs fill in the gaps between the highly thermally conductive graphene fillers, and create a limited number of highly conductive thermal paths (see Figure g), which results in steeper increase in the thermal conductivity (Figure b).…”

Section: Resultsmentioning

confidence: 66%

Thermal Properties of the Binary‐Filler Hybrid Composites with Graphene and Copper Nanoparticles

Barani

Mohammadzadeh

Geremew

et al. 2019

Adv Funct Materials

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203

160

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The thermal properties of epoxy‐based binary composites comprised of graphene and copper nanoparticles are reported. It is found that the “synergistic” filler effect, revealed as a strong enhancement of the thermal conductivity of composites with the size‐dissimilar fillers, has a well‐defined filler loading threshold. The thermal conductivity of composites with a moderate graphene concentration of fg = 15 wt% exhibits an abrupt increase as the loading of copper nanoparticles approaches fCu ≈ 40 wt%, followed by saturation. The effect is attributed to intercalation of spherical copper nanoparticles between the large graphene flakes, resulting in formation of the highly thermally conductive percolation network. In contrast, in composites with a high graphene concentration, fg = 40 wt%, the thermal conductivity increases linearly with addition of copper nanoparticles. A thermal conductivity of 13.5 ± 1.6 Wm−1K−1 is achieved in composites with binary fillers of fg = 40 wt% and fCu = 35 wt%. It has also been demonstrated that the thermal percolation can occur prior to electrical percolation even in composites with electrically conductive fillers. The obtained results shed light on the interaction between graphene fillers and copper nanoparticles in the composites and demonstrate potential of such hybrid epoxy composites for practical applications in thermal interface materials and adhesives.

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Section: Resultsmentioning

confidence: 66%

Thermal Properties of the Binary‐Filler Hybrid Composites with Graphene and Copper Nanoparticles

Barani

Mohammadzadeh

Geremew

et al. 2019

Adv Funct Materials

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203

160

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“…The material was processed in-house to find the optimum aspect ratio, lateral dimensions, and thickness of FLG fillers. [79] The samples were prepared in the form of disks with the diameter of 25.6 mm and thicknesses from 0.9 to 1.0 mm (see Table SI of the Supporting Information for the exact thickness of each individual sample). The theory and experimental studies [90][91][92][93][94] suggest that the higher the aspect ratio of the conductive fillers, the lower is the filler concentration required to achieve electrical percolation.…”

Section: Materials Synthesismentioning

confidence: 99%

“…The electrical percolation and resulting electrical conduction via the entire composite sample are likely to improve the EMI shielding efficiency. [68,72,79] For this reason, the strategy in materials synthesis was to achieve the electrical and thermal percolation by selecting the right filler dimensions and loading but avoiding the rolling and bending of the fillers. In the first batch, referred to as GF-A, the lateral dimensions of the FLG fillers were in the range from ≈1.5 to 10 µm and the thicknesses were in the range from 0.35 to 12 nm, which corresponds to 1-40 graphene monolayers, respectively.…”

Section: Materials Synthesismentioning

confidence: 99%

“…[64][65][66] The intrinsic thermal conductivity of graphene can exceed that of the highquality bulk graphite, which by itself is high-2000 W m −1 K −1 at RT. [68,72,79] The latter is due to the fact that the heat conduction properties of FLG experience less degradation upon exposure to the matrix material. [68,[70][71][72][73][74][75][76] 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%

“…[68,72,79] The latter is due to the fact that the heat conduction properties of FLG experience less degradation upon exposure to the matrix material. [79] Given the importance of electrical percolation for EMI shielding and thermal percolation for TIM applications, we examined the properties of the designed graphene composites over a wide range of the graphene and FLG loading fractions. It should be noted that the mechanical flexibility and excellent coupling of graphene to polymer matrix make it more favorable filler material than other carbon allotropes.…”

Section: Introductionmentioning

confidence: 99%

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Dual‐Functional Graphene Composites for Electromagnetic Shielding and Thermal Management

Kargar

Barani

Balinskiy

et al. 2018

Adv Elect Materials

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192

132

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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...

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Design and Optimization of Lamellar Phase Change Composites for Thermal Energy Storage

et al. 2020

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Phase change materials offer thermal energy storage (TES) and are often integrated with high conductivity materials to increase power density. However, the design and optimization of such composites are historically based on intuition, as the computational techniques used to predict behavior in these systems are generally too expensive to perform parametric studies. Herein, a general design framework is developed and demonstrated that is optimized for TES in parallel lamellar structures, to identify the critical pitch required to treat the composite as a single effective medium and the optimum volume fraction of high conductivity material in the lamellar composite. The optimization criteria is tested experimentally using 3D printed AlSi12 alloy and octadecane. The composite system exhibits a critical pitch between a lamella of 1 mm and the optimum volume fraction for the high conductivity material is 0.6–0.8. The design principles demonstrated here show that the size and volumes of conductive materials are much larger than the current state of the art, and this framework provides a holistic approach to design for such future materials for TES applications.

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

Cited by 256 publications

References 83 publications

Thermal Properties of the Binary‐Filler Hybrid Composites with Graphene and Copper Nanoparticles

Thermal Properties of the Binary‐Filler Hybrid Composites with Graphene and Copper Nanoparticles

Dual‐Functional Graphene Composites for Electromagnetic Shielding and Thermal Management

Design and Optimization of Lamellar Phase Change Composites for Thermal Energy Storage

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