Supporting Information

Introduction

Table S1. The summary of in-plane thermally conductive paper-like composites.

Sample

Fabrication method

Thermal

Conductivity

(W m-1 K-1)

Measurement method

Year [Ref]

Nanofibrillated cellulose(NFC)/BN

Vacuum filtration

145.7 (50 wt%)

Steady-state method

2014[1]

NFC/RGO

LBL assembly

12.6(--)

Laser flash technique

2017[2]

PVA/BN@PDA

Vacuum filtration

5.4 (10 vol% )

Laser flash technique

2015[3]

PET/RGO

Graphene ink coating method

90 (--)

Optothermal raman technique

2014 [4]

CNF /BN nanotube

Vacuum filtration

21.39(25 wt%)

Laser flash technique

2017[5]

Cellulose/ RGO

Vacuum filtration

9(6 %)

Laser flash technique

2017[6]

Poly (vinylidene fluoride-co-hexafluoropropylene) / RGO

Solvent casting

19.5(27.2 wt%)

Laser flash technique

2016 [7]

Polyimides (PI)/BN

Spin casting

17.5, 5.4(60 vol%)

Temperature wave analysis (TWA) method, Laser flash technique

2013 [8]

SiC nanowire/cellulose microcrystal

Vacuum filtration

34(50 vol%)

Laser flash technique

2016 [9]

PDDA/BN nanosheets

Vacuum filtration

212.8(90 wt%)

Steady-state method

2017 [10]

RGO paper

Solvent casting

61

Laser flash technique

2015 [11]

RGO paper

Solvent casting

1100

Laser flash technique

2014 [12]

RGO paper

Vacuum filtration

1043.5

Laser flash technique

2014[13]

RGO paper

Electro-spray deposition

1238.3

Self-heating method

2014 [14]

Graphitic paper

Polyimide graphitization

1750

Laser flash technique

2014 [12]

RGO paper

Vacuum filtration

1529

Self-heating method

2017 [15]

RGO paper

Vacuum filtration

1940

Laser flash technique

2017 [16]

RGO paper

Vacuum filtration

1390

Laser flash technique

2015 [17]

RGO/carbon fiber paper

Vacuum filtration

977

Laser flash technique

2014 [18]

Fig. S1. Schematic representation of the preparation process of NR/BN and NR/GNPs composites.

Experimental section

Materials. Graphene nanoplatelets (cz-030, Xiamen Knano Graphene Technology, Co., Ltd, China) with the particle size of 20-30 um and the density of 2.25 g/cm3, BN flakes (Qinghuangdao Yinuo Advanced Material Co., Ltd, China) with the particle size of 10-15 um and the density of 2.25 g/cm3 and NR lateral (Yiwu Taiyou Hu Trade Co., Ltd., China) with the solid content of 61.79 % were used. Polyvinyl Alcohol (PVA1788) as dispersant was purchased from Chengdu Kelong Chemical reagent Co., Ltd. The curing agents including sulfur, zinc diethyl dithiocarbamate (ZDC), Zink oxide (ZnO) were commercially available industrial products. Commercial natural graphite paper (NG paper) with the thickness of 100 um and of 288 W m-1 K-1 was purchased from Beijing Jinglong Tetan Co Ltd. Cu foil with the thickness of 76 um and of 380 W m-1 K-1 was purchased from Shanghai Huhong Metal Material Co Ltd. The materials were used as received without any purification and chemical treatment. The SEM images of fillers and optical images of the comparison samples were shown in the supporting information Fig. S2.

Preparation of NR/BN and NR/GNPs composites

NR/GNPs and NR/BN composites were fabricated by simple vacuum filtration method. As shown in the supporting information Fig. S1, a certain amount of BN or GNPs and PVA (BN or GNPs: PVA=100: 5, w/w) were mixed in the deionized water via ultrasonic bath treatment for 30 min, followed by adding the NR latex. Then, a certain amount of curing agents including sulfur (2 phr), ZDC (1 phr) and ZnO (0.5 phr) was mixed into the suspension. The suspension was stirred for 12 h at room temperature. To form composite films, the mixture was vacuum filtrated with filter membrane (220 nm) and then allowed for water evaporation at room temperature for 12 h. Lastly, the resulted films was heat compressed for 6 h at 60 °C and 10 MPa. Mechanical compression improved the contact of the thermally conductive fillers and chased away the air bubbles. The composites were designated according to the volume content of thermally conductive fillers.

Characterization. The as-obtained composite films were characterized by scanning electron microscope (SEM, JOEL JSM-5900LV, Japan), X-ray diffraction (XRD, Cu Kα radiation, Rigaku, Ultima IV, Japan), insulation resistance tester (U2683, Eucol Electronic Technology Co., Ltd, China) and universal material testing machine (Instron 5967, USA). The k of the composites was tested at 25 °C with the laser flash technique (Netzsch, Pyroceram 9606 as reference sample, LFA 467, USA). The k was calculated by , where λ, α, ρ and Cp represent the k, thermal diffusivity, density and specific heat capacity of the composites, respectively. The EMI shielding performance of the composites in the X-band (8.2-12.4 GHz) was characterized by a vector network analyzer (Agilent N5230, USA). The hardness and modulus of the composite films were tested by a nano-indentation tester (Keysight G200, USA) equipped with Berkovich indenter. Tensile properties of the composites were tested at 25° C by a universal material testing machine (Instron 5967, USA) with a cross-heat speed of 0.4 mm/min.

Results and Discussions

Fig. S2. SEM images of (a) pure NR, (b) pure GNPs and (c) BN, optical images of (d) commercial NG paper and (e) copper foil.

The orientation of fillers with hexagonal crystal system such as BN can be characterized by XRD, due to that the diffraction patterns obtained from the top and side planes of hexagonal crystal are different. We found that the orientation of GNPs in polymer matrix can also been characterized by XRD patterns as shown in the Fig. S3. The XRD pattern obtained from cross section and surface of 27.48GNPs composites are quite different. The XRD pattern obtained from surface show sharp (002) and (004) diffraction peaks, while the XRD pattern obtained from cross section show sharp (002), (100), (101), (110) and (112) diffraction peaks.

Fig. S3. XRD patterns of pure GNPs filler and 27.48GNPs composites.

Fig. S4. (a) Thermal conductivity of 27.48GNPs and 55.85BN composites as function of temperature, (b) thermal diffusivity and specific heat of 27.48GNPs and 55.85BN composites as function of temperature.

Fig. S4a shows the and of 27.48GNPs and 55.85BN composites as function of temperature. The thermal conductivity of 55.85BN decreased slightly with increasing temperature, consistent with the anhar-monic phonon–phonon scattering that is dominant in highly crystalline materials (the content of BN is 55.85 vol%).[16] However, the thermal conductivity of 27.48GNPs increases for a certain degree with increasing temperature. In non-crystalline materials the change of thermal conductivity is also dependent on the change of specific heat. One can see that the specific heat of 27.48GNPs rapidly increases with increasing temperature.

Fig. S5. Volume resistivity of NR/BN composites with different content of BN.

As presented in Fig. S5, the volume resistivity obtained from NR/BN composites was in the range of 3.081014-3.631015, which is far beyond the electrical insulation range (), which guarantees the application of such TIMs in some special electrical device fields.

Table. S2 Comparison of EMI shielding effectiveness of composites in the X-band frequency range.

Sample

Density(g cm-3)

Thickness(mm)

SE(dB)

SSE(dB cm2 g-1)

[Ref]

Cellulose/CNTs

1.35

0.15

35

~1372.4

[19]

PEEK/GPPS/MWCNT

1.34

0.18

10.5

~435.3

[20]

PLLA/MWCNT

>1.25

1.5

30

<160

[21]

Epoxy/CNTs

>1.2

2

33

<137.5

[22]

PS/ RGO

>1.04

2.5

45.1

<173.5

[23]

PEDOT:PSS/Graphene

0.96

0.8

70

~911.5

[24]

Graphene/Fe3O4 film

0.78

0.3

24

~1025.6

[25]

Copper film

8.9

0.013

115

～9939.9

[26]

RGO film

1.63

0.0084

20

~14607.1

[12]

RGO film

1.63

0.031

130

～25727.3

[26]

NR/GNPs

1.14

0.071

33.96

~4195.7

This work

Comparison of EMI shielding effectiveness of composites in the X-band frequency range was made in Table S2. Clearly, our NR/GNPs composites show the highest value of SSE in the polymer composites. Noted that RGO film possess the highest value of SSE in all the composites (25727.3 dB cm2 g-1).[26]

Fig. S6. The temperature difference ∆ at 240 s which was be used to calculate the contact thermal resistance.

Fig. S7. Schematic illustration of contact thermal resistance of TIMs application.

Fig. S7 presented the schematic illustration of contact thermal resistance of TIMs application. Contact resistance is composed of two parallel contact resistances: (1) conduction resistance at the contact points and (2) conduction resistance across the air gap of non-contacting area.

References

[1] H. Zhu, Y. Li, Z. Fang, J. Xu, F. Cao, J. Wan, C. Preston, B. Yang, L. Hu, Highly Thermally Conductive Papers with Percolative Layered Boron Nitride Nanosheets, ACS Nano 8 (2014) 3606.

[2] N. Song, D. Jiao, S. Cui, X. Hou, P. Ding, L. Shi, Highly Anisotropic Thermal Conductivity of Layer-by-Layer Assembled Nanofibrillated Cellulose/Graphene Nanosheets Hybrid Films for Thermal Management, ACS Applied Materials & Interfaces 9 (2017) 2924-2932.

[3] H. Shen, J. Guo, H. Wang, N. Zhao, J. Xu, Bioinspired Modification of h-BN for High Thermal Conductive Composite Films with Aligned Structure, ACS Applied Materials & Interfaces 7 (2015) 5701-5708.

[4] H. Malekpour, K.H. Chang, J.C. Chen, C.Y. Lu, D.L. Nika, K.S. Novoselov, A.A. Balandin, Thermal Conductivity of Graphene Laminate, Nano Letters 14 (2014) 5155-5161.

[5] X. Zeng, J. Sun, Y. Yao, R. Sun, J.B. Xu, C.P. Wong, A Combination of Boron Nitride Nanotubes and Cellulose Nanofibers for the Preparation of a Nanocomposite with High Thermal Conductivity, ACS Nano 11 (2017) 5167-5178.

[6] N. Song, X. Hou, L. Chen, S. Cui, L. Shi, P. Ding, A Green Plastic Constructed from Cellulose and Functionalized Graphene with High Thermal Conductivity, ACS Appl Mater Interfaces 9 (2017) 17914-17922.

[7] P. Kumar, S. Yu, F. Shahzad, S.M. Hong, Y.-H. Kim, C.M. Koo, Ultrahigh electrically and thermally conductive self-aligned graphene/polymer composites using large-area reduced graphene oxides, Carbon 101 (2016) 120-128.

[8] M. Tanimoto, T. Yamagata, K. Miyata, S. Ando, Anisotropic Thermal Diffusivity of Hexagonal Boron Nitride-Filled Polyimide Films: Effects of Filler Particle Size, Aggregation, Orientation, and Polymer Chain Rigidity, ACS Applied Materials & Interfaces 5 (2013) 4374-4382.

[9] Y. Yao, X. Zeng, G. Pan, J. Sun, J. Hu, Y. Huang, R. Sun, J.B. Xu, C.P. Wong, Interfacial Engineering of Silicon Carbide Nanowire/Cellulose Microcrystal Paper toward High Thermal Conductivity, ACS Appl Mater Interfaces 8 (2016) 31248-31255.

[10] Y. Wu, Y. Xue, S. Qin, D. Liu, X. Wang, X. Hu, J. Li, X. Wang, Y. Bando, D. Golberg, Y. Chen, Y. Gogotsi, W. Lei, BN Nanosheet/Polymer Films with Highly Anisotropic Thermal Conductivity for Thermal Management Applications, ACS Appl Mater Interfaces 9 (2017) 43163-43170.

[11] J.D. Renteria, S. Ramirez, H. Malekpour, B. Alonso, A. Centeno, A. Zurutuza, A.I. Cocemasov, D.L. Nika, A.A. Balandin, Strongly Anisotropic Thermal Conductivity of Free-Standing Reduced Graphene Oxide Films Annealed at High Temperature, Advanced Functional Materials 25 (2015) 4664-4672.

[12] B. Shen, W. Zhai, W. Zheng, Ultrathin Flexible Graphene Film: An Excellent Thermal Conducting Material with Efficient EMI Shielding, Advanced Functional Materials 24 (2014) 4542-4548.

[13] N.-J. Song, C.-M. Chen, C. Lu, Z. Liu, Q.-Q. Kong, R. Cai, Thermally reduced graphene oxide films as flexible lateral heat spreaders, J. Mater. Chem. A 2 (2014) 16563-16568.

[14] G. Xin, H. Sun, T. Hu, H.R. Fard, X. Sun, N. Koratkar, T. Borca-Tasciuc, J. Lian, Large-Area Freestanding Graphene Paper for Superior Thermal Management, Advanced Materials 26 (2014) 4521-4526.

[15] C. Teng, D. Xie, J. Wang, Z. Yang, G. Ren, Y. Zhu, Ultrahigh Conductive Graphene Paper Based on Ball-Milling Exfoliated Graphene, Advanced Functional Materials 27 (2017) 1700240.

[16] L. Peng, Z. Xu, Z. Liu, Y. Guo, P. Li, C. Gao, Ultrahigh Thermal Conductive yet Superflexible Graphene Films, Advanced Materials 29 (2017) 1700589.

[17] P. Kumar, F. Shahzad, S. Yu, S.M. Hong, Y.-H. Kim, C.M. Koo, Large-area reduced graphene oxide thin film with excellent thermal conductivity and electromagnetic interference shielding effectiveness, Carbon 94 (2015) 494-500.

[18] Q.-Q. Kong, Z. Liu, J.-G. Gao, C.-M. Chen, Q. Zhang, G. Zhou, Z.-C. Tao, X.-H. Zhang, M.-Z. Wang, F. Li, R. Cai, Hierarchical Graphene-Carbon Fiber Composite Paper as a Flexible Lateral Heat Spreader, Advanced Functional Materials 24 (2014) 4222-4228.

[19] L.-Q. Zhang, B. Yang, J. Teng, J. Lei, D.-X. Yan, G.-J. Zhong, Z.-M. Li, Tunable electromagnetic interference shielding effectiveness via multilayer assembly of regenerated cellulose as a supporting substrate and carbon nanotubes/polymer as a functional layer, Journal of Materials Chemistry C 5 (2017) 3130-3138.

[20] R. Na, J. Liu, G. Wang, S. Zhang, Light weight and flexible poly(ether ether ketone) based composite film with excellent thermal stability and mechanical properties for wide-band electromagnetic interference shielding, RSC Advances 8 (2018) 3296-3303.

[21] K. Zhang, G.-H. Li, L.-M. Feng, N. Wang, J. Guo, K. Sun, K.-X. Yu, J.-B. Zeng, T. Li, Z. Guo, M. Wang, Ultralow percolation threshold and enhanced electromagnetic interference shielding in poly(l-lactide)/multi-walled carbon nanotube nanocomposites with electrically conductive segregated networks, Journal of Materials Chemistry C 5 (2017) 9359-9369.

[22] Y. Chen, H.-B. Zhang, Y. Yang, M. Wang, A. Cao, Z.-Z. Yu, High-Performance Epoxy Nanocomposites Reinforced with Three-Dimensional Carbon Nanotube Sponge for Electromagnetic Interference Shielding, Advanced Functional Materials 26 (2016) 447-455.

[23] D.-X. Yan, H. Pang, B. Li, R. Vajtai, L. Xu, P.-G. Ren, J.-H. Wang, Z.-M. Li, Structured Reduced Graphene Oxide/Polymer Composites for Ultra-Efficient Electromagnetic Interference Shielding, Advanced Functional Materials 25 (2015) 559-566.

[24] N. Agnihotri, K. Chakrabarti, A. De, Highly efficient electromagnetic interference shielding using graphite nanoplatelet/poly(3,4-ethylenedioxythiophene)–poly(styrenesulfonate) composites with enhanced thermal conductivity, RSC Advances 5 (2015) 43765-43771.

[25] W.-L. Song, X.-T. Guan, L.-Z. Fan, W.-Q. Cao, C.-Y. Wang, Q.-L. Zhao, M.-S. Cao, Magnetic and conductive graphene papers toward thin layers of effective electromagnetic shielding, Journal of Materials Chemistry A 3 (2015) 2097-2107.

[26] E. Zhou, J. Xi, Y. Liu, Z. Xu, Y. Guo, L. Peng, W. Gao, J. Ying, Z. Chen, C. Gao, Large-area potassium-doped highly conductive graphene films for electromagnetic interference shielding, Nanoscale 9 (2017) 18613-18618.