Supplementary content

Toward high efficiency thermally conductive and electrically insulating pathways

through uniformly dispersed and highly oriented graphites close-packed with SiC

Xiaomeng Zhang, Jiajia Zhang, Xianlong Zhang, Chunhai Li, Jianfeng Wang, Huan Li,

Lichao Xia, Hong Wu*, Shaoyun Guo*, Shaoyun Guo*

The State Key Laboratory of Polymer Materials Engineering, Polymer Research

Institute of Sichuan University, Chengdu 610065, China

*, Shaoyun Guo* To whom correspondence should be addresses. (Prof. Wu, Email: wh@scu.edu.cn, Fax: 86-028-85466077)

** To whom correspondence should be addresses. (Prof. Guo, Email: sguo@scu.edu.cn , Fax: 86-028-85405135)

1. The selection of SiC

Fig. S1. (a) One of SEM images that was used to calculate distances between adjacent

graphites, (b) distance distribution and major data of statistics, (c) size distribution

and main parameters of silicon carbide particles.

As stated above, connections between graphites were reduced sharply due to the

uniform dispersion state and high orientation degrees, thus the 3-D phonon transport

networks were also destroyed reasonably. Then, in order to reconnect graphites and

construct new and effective thermally conductive pathways again, at the meantime,

keeping the high electrical resistivity of the composites, SiC particles with low

electrical conductivity were added. For the purpose of a desirable synergetic effect,

distances between adjacent graphites were counted. The average was about 2.25 μm,

as shown in Fig. S1. Therefore, SiC with an average size of 2.97 μm was chosen as

the second filler. There were two main reasons for this selection. The first one was

that the size of SiC was big enough to contact with two adjacent graphites, and on the

other hand, they would not damage the orientation degrees of graphites seriously. As

a result, the thermal conductivity could be improved, and the composites were also

remained as electrical insulators.

2. Accurate compositions of the composites filled with hybrid fillers

Table S1. Accurate compositions of the composites filled with hybrid

fillers

In the MSE system

SiC Graphite HDPE

0 33wt% 67wt%

10wt% 29.7wt% 60.3wt%

20wt% 26.4wt% 53.6wt%

In the CM system

0 28.5wt% 71.5wt%

10wt% 25.65wt% 64.35wt%

20wt% 22.8wt% 57.2wt%

3. Morphologies of the composites filled with hybrid fillers

Fig. S2. SEM-EDS images of the multistage stretching extruded samples filled with different

content of SiC particles.

10 and 20 wt% silicon carbide particles with respect to the total quality were added

into the composites, basing on the rule that keeping the ratio between HDPE and

graphites as a constant, 67/33 in the multistage stretching extruded composites and

71.5/28.5 in the compression molded samples. And the detail distribution of SiC was

observed by SEM-EDS along the melt flow direction, as shown in Fig. S2. It can be

clearly seen that with the addition of SiC particles, the dispersion state of graphites

almost had no changes, and SiC particles also dispersed uniformly in the multistage

stretching extruded composites.

4. Orientation degrees of graphites in the multistage stretching extruded samples filled

with hybrid fillers

Fig. S3. XRD patterns of the multistage stretching extruded samples filled with different

content of SiC.

Then, XRD was applied again to evaluate the change of orientation degrees of

graphites with the addition of SiC. As stated above, the horizontally and vertically

oriented graphites correspond to the (002) and (10L) peaks respectively, and the ratio

of intensity between these two peaks describes orientation degrees of them precisely.

Then Fig. S3 showed the XRD profiles of samples with different content of SiC

particles and main parameters were also listed in Table S2. These results indicated

that the relative intensity ratio between two peaks changed a little with the addition of

SiC particles, which ranged from 959 to 1198, which could strongly prove that SiC

particles with appropriate sizes had no obvious effect on the morphology of graphites.

Table S2. The intensities of (002) and (10L) peaks and their ratios

Samples I(002) I(10L) I(002)/I(10L)

MSE-33wt% Gt 273735 280 978

MSE-33wt%Gt+10wt%SiC 147471 123 1198

MSE-33wt%Gt+20wt%SiC 93105 97 959

4. Electrical resistivities of the multistage stretching extruded samples filled with hybrid

fillers.

Fig. S4. Electrical resistivities of the multistage stretching extruded samples filled

with hybrid fillers.

With such perfect structures, electrical resistivities of the composites with hybrid

fillers prepared by multistage stretching extrusion were also measured along two

directions, as shown in Fig. S4. It can be clearly seen that with the addition of SiC,

electrical resistivities of the final composites were always kept at a high level, which

could meet the requirements of electronic devices.

5. Rheological properties

Fig. S5. Rheological properties of the multistage stretching extruded samples filled

with different content of SiC.

6. Comparison with previous literatures in different views

Table S3 Thermal conductivities (TC) along the orientation direction and anisotropic

index (AI) in the region of thermally conductive and electrically insulating

composites ( focusing on non-film materials, thickness ≧ 1 mm)

Ref Matrix Filler Content TC(W/(m×K)) AI Processing method

/Testing method

1 Epoxy BN 40wt% 0.9 - Magnetic alignment/Laser flash (Transient)

2 Silicone BN 9vol% 0.55 2.5 Magnetic alignment/Laser flash (Transient)

3 Epoxy BN 40wt% 2.6 5.2 Magnetic alignment/Laser flash (Transient)

4 Epoxy Si3N4 60vol% 9.2 1.6 Solution blending/Laser flash (Transient)

This workPE Graphite 33wt%

(14.4vol%) 3.49 5.8 Melt blending/Laser flash (Transient)

PE Graphite, SiC

46.4wt%(24.3vol%) 3.8 5.1 Melt blending/

Laser flash (Transient)

Previously, in the region of non-film polymer-matrix composites, magnetic assisted

method was the major method, even the only method, which can force anisotropic

thermally conductive fillers into the alignment structure. But it could only be used to

modify thermoset or low viscosity polymers. However, for practical applications, melt

blending is much more effective and environmentally friendly. As shown in Table S3,

it can be clearly seen that anisotropic fillers could also be forced into highly oriented

structures through the multistage stretching extrusion, and the AI was even larger than

those of other systems. Furthermore, these results also demonstrated that thermally

and electrically conductive fillers, such as graphite, have much higher filling

efficiency than other ceramic fillers, since a relatively larger thermal conductivity was

achieved with a lower additive amount.

Table S4 Thermal conductivities of different thermally conductive and electrically

insulating composites without oriented fillers

Ref Matrix Filler Content TC(W/(m×K))

Enhancement(%)

Processing method/Testing method

5 Epoxy BNNT 30wt% 2.8 1020 Solution blending/Laser flash (Transient)

6 Epoxy SiC,Al2O3 50wt% 1.2 500 Solution blending/Laser flash (Transient)

7 PP AlN 52.5vol% 1.2 380 Solution blending/Laser flash (Transient)

8 PIb BN 40wt% 0.78 387 In situ polymerization/Hot-wire (Transient)

9 Epoxy BNNS, AgNPs 25vol% 3 1100 Solution blending/Laser flash (Transient)

10 PE/PPSc CNT,BN 15.85vol% 0.97 65 Melt blending/Steady state

11 PP CNT,CBd,Al2O3 57.5wt% 0.68 172 Melt blending/Laser flash (Transient)

This work PE Graphite, SiC 46.4wt%

(24.3vol%)

3.8 995 Melt blending/Laser flash (Transient)

1.68 384 Melt blending/Hot-disk (Transient)

As shown in Table S4, generally, comparing with composites filled with single

ceramic filler, multistage stretching extruded samples had much higher thermal

conductivity and filling efficiency [7,8]. It should be noted that the ceramic filler with

high aspect ratio or decorated with metal particles also had rather high filling

efficiencies, but the preparation process was very complex [5,9]. Then, comparing

with other melt blending method, multistage stretching extrusion could make full use

of the advantages of fillers, thus the final thermal conductivity and the enhancement

were improved sharply [10,11].

Table S5 Comparison with other thermally conductive and electrically insulating

composites filled with surface coated fillers

Ref Matrix Filler Content TC(W/(m×K))

Enhancement（%） Processing/Testing method

12 PI BN-MWCNTs 3wt% 0.38 111 In situ polymerization/Laser flash (Transient)

13 PI AlO(OH)-MWCNTs 5wt% 0.42 140 In situ polymerization/

Hot-disk (Transient)

14 PUa HPUb-MWCNT 1wt% 0.29 66 Solution blending/Steady state

15 Epoxy Silica-Reduced graphene oxide 1wt% 0.32 60 Solution blending/

Laser flash (Transient)

16 Epoxy Silica-Graphene 8wt% 0.3 76 Solution blending/Mathis TCi (Transient)

17 Epoxy Silica-MWCNTs 1wt% 0.24 66 Solution blending/Steady state

18 Epoxy Silica-Silver nanowire 4vol% 1.05 400 Solution blending/

Hot-wire (Transient)

19 Epoxy Nano silica –MWCNTs 1.25wt% 0.42 110 Solution blending/

Laser flash (Transient)

20 PBTc Silica-Graphite23vol% 2 809 Melt blending/

Laser flash (Transient)46vol% 5.2 2264

This work

PE Graphite33wt%(14.4vol

%)1.43 309 Melt blending/

Hot-disk (Transient)

PE Graphite 33wt% (14.4vol%) 3.49 906 Melt blending/

Laser flash (Transient)

PE Graphite, SiC 46.4wt%(24.3vol%) 1.68 384 Melt blending/

Hot-disk (Transient)

PE Graphite, SiC 46.4wt%(24.3vol%) 3.8 995 Melt blending/

Laser flash (Transient)a: Polyurethane; b: hyperbranched poly(urea-urethane); c: polybutylene terephthalate.

As well known, carbon based fillers with high intrinsic thermal conductivities have

much more filling efficiencies [21]. Traditionally, they should be modified by surface

coating to meet the requirements of thermally conductive and electrically insulating

composites. However, since the productive rate of such unique fillers is very low and

the dispersibility of nanofillers is also very poor, the additive amount of them was

always kept in a low level. From the results shown in Table S5, we can see that the

enhancement and the final thermal conductivity of this work are always much higher

than the maximum of other works, which demonstrates that the structure control is

much more effective in enhancing the thermal conductivity of final composites.

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