Highly in-Plane Thermally Conductive Composite Films from

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Highly In-Plane Thermally Conductive Composite Films from Hexagonal Boron Nitride Microplatelets Assembled with Graphene Oxide Ziming Shen, and Jiachun Feng ACS Appl. Nano Mater., Just Accepted Manuscript • DOI: 10.1021/acsanm.7b00041 • Publication Date (Web): 22 Dec 2017 Downloaded from http://pubs.acs.org on December 23, 2017

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ACS Applied Nano Materials

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Highly In-Plane Thermally Conductive Composite Films from Hexagonal Boron Nitride Microplatelets Assembled with Graphene Oxide

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Ziming Shen, and Jiachun Feng*

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State Key Laboratory of Molecular Engineering of Polymers, Department of Macromolecular

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Science and Laboratory of Advanced Materials, Fudan University, Shanghai 200433, China.

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E-mail: [email protected]. Tel: 86 (21) 6564 3735. Fax: +86 (21) 6564 0293.

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KEYWORDS: hexagonal boron nitride microplatelets, graphene oxide, composite film, in-plane

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thermal conductivity, mechanical flexibility, electrical insulation.

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ABSTRACT: With the development of portable and flexible devices, demands for high

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performance thermal management materials with high in-plane thermal conductivity (TC),

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mechanical flexibility and electrical insulation are growing. Hexagonal boron nitride (BN) is a

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promising thermally conductive filler due to its high in-plane TC and electrical insulation. In this

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work, taking full advantage of good film-forming feature of graphene oxide (GO) suspension and

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its ability to stably disperse BN microplatelets (BNMPs) in the aqueous medium, the

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GO/BNMPs composite films with high in-plane TCs were prepared by a simple cast drying

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method. The structure characterization demonstrated that GO can induce BNMPs to preferably

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arrange in-plane orientation in the composite films. The resultant composite films possessed a

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maximum in-plane TC value of 10.3 W/m·K at 50 wt % BNMPs. Moreover, the films exhibited

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excellent mechanical flexibility and satisfactory electrical insulation. The proposed method of

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fabricating BNMPs based composite films in this work is facile handling, eco-friendly and

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suitable for large scales production, and therefore enables potential applications in the flexible

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electronics.

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1. INTRODUCTION

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With the continuing development of miniaturization and integration of smart electronic

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devices, efficient heat dissipation has become a crucial issue in electronics.1,2 The demands for

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high performance thermal management materials with high in-plane thermal conductivity (TC),

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mechanical flexibility and electrical insulation are growing.3 Hexagonal boron nitride (BN) is a

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promising thermally conductive filler due to its high TC, high thermal stabilities and excellent

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electrical insulation.4-8 As a typical two-dimensional sheets, BN has an anisotropic feature in TC.

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Its in-plane TC can reach 400 W/m·K, much higher than that of the through-plane (2 W/m·K).4

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Thus, how to take full advantage of its in-plane TC to fabricate the composites with high TC has

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attracted great attentions.

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Forcing BN into the alignment structure has been regarded as an effective route to achieve

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highly in-plane thermally conductive materials.9 Previous studies have proposed several

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strategies to rationally control the arrangements of BN in the composites. One way is to exfoliate


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BN microplatelets (BNMPs) into BN nanosheets (BNNSs) and subsequently assembling into

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BNNSs based composites.10-13 For example, Xu’s group obtained the exfoliated BNNSs by

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sonication and prepared poly(vinyl alcohol) (PVA)/BNNSs composite films with a TC value of

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6.9 W/m·K at 94 wt % BNNSs.12 They also prepared graphene oxide (GO)/BNNSs composite

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films, which have an in-plane TC value of 29.8 W/m·K at 95 wt % BNNSs.13 Wang et al

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fabricated polystyrene/BNNSs composites with high in-plane oriented BNNSs and the in-plane

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TC of the resulting composite containing 13.4 vol % BNNSs reached 8.0 W/m·K.11 However, for

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the frequently-used exfoliation methods (such as sonication and ball milling), there existed some

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drawbacks, including low production yield14, long exfoliation time15, high energy

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consumption16,17 and the use of environmentally-unfriendly solvents18, which limit their practical

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application. Moreover, the exfoliation process unavoidably led lateral sizes of BNMPs to reduce

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severely owing to strong forces, which was detrimental to heat conducting.13,19,20 If there are

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strategies to directly prepare BN based composites with high in-plane TCs using the un-

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exfoliated BNMPs, it will be more economical and operable for the industry application

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compared with the BNNSs composites due to free of the exfoliation process. Recently, some

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studies have proposed various methods to fabricate BNMPs based composites. For example, Xie

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et al and Shen et al prepared PVA/BNMPs composites by a doctor blading method. They found

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that BNMPs had a high in-plane orientation due to strong shear force and the resultant

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composites had in-plane TCs of 5.4 W/m·K and 3.92 W/m·K at 10 vol % and 5.9 vol % BNMPs,

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respectively.21,22 Zhang et al and Song et al fabricated polyethylene/BNMPs and PVA/BNMPs


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composites with high in-plane oriented BNMPs by multistage stretching extrusion9 and

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stretching at room temperature23, respectively. Besides shear and stretching, electrical field or

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magnetic field can also induce BNMPs to align along in-plane direction in the composites.24,25

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These pioneering studies have demonstrated it is feasible to prepare highly in-plane thermally

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conductive BNMPs based composites by controlling their alignment. However, considering the

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significant importance of thermally conductive materials in electronics, a simple and convenient

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method to fabricate the BNMPs based composites with high in-plane TCs is still highly required.

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In this work, taking full advantage of GO suspension’s good film-forming feature and its

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ability to stably disperse BNMPs in the aqueous medium, we proposed a facile method to

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prepare GO-BNMPs composite films with high in-plane TC. The homogenous GO/BNMPs

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suspension was firstly obtained and then the composite films were fabricated by a simple cast

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drying method. Our results demonstrated that GO can induce BNMPs to preferably arrange in-

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plane orientation and the resultant GO-BNMPs composite film containing 50 wt % of BNMPs

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had an in-plane TC of 10.3 W/m·K. The simple method to prepare BNMPs based materials with

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high in-plane TCs enables potential applications in the flexible electronics.

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2 EXPERIMENTAL DETAILS

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2.1 Materials. Graphite oxide sheets were purchased from The Sixth Element Materials

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Technology Company (Changzhou, China), which was prepared by chemical oxidation of

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graphite. BNMPs (99.5% metals basis) were purchased from Alfa Aesar.


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2.2 Preparation of GO-BNMPs composite films. The GO-BNMPs composite films were

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fabricated by a cast drying method. In brief, the GO solution (5 mg/mL) was prepared by

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dispersing graphite oxide uniformly in water by bath sonication (40 kHz, 30 min) followed by

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stirring (1000 rpm, 12 h). A certain amount of BNMPs were added into the above GO solution to

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obtain a homogenous suspension with an extra sonication (40 kHz, 30 min) and then magnetic

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stirring (1000 rpm, 12 h). The obtained suspension was poured into a Teflon mold with the

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dimensions of 60 mm×60 mm and dried at 40 oC in an air dry oven to fabricate GO-BNMPs

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composite films with the thickness of 50 ± 5 µm, which were denoted as BNx and x represented

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the weight fraction of BNMPs. Pure GO film was also prepared through the identical procedure.

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2.3 Characterization. X-ray photoelectron spectrometry (XPS) was carried out to study the

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functional groups of GO on ESCALAB 250Xi X-ray photoelectron electron spectrometer

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(Thermo Fisher Scientific, USA) using monochromated Al Kα beams as the excitation source

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(1486.6 eV). The morphologies of GO was observed by a Tecnai G2 TWIN transmission

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electron microscopy (TEM) (FEI, USA). Scanning electron microscope (SEM) studies were

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performed on an Ultra 55 (Zeiss, Germany) at an accelerating voltage of 5 kV. Powder X-ray

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diffraction (XRD) patterns were taken on an X-ray diffractometer (PANalytical, Netherlands)

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using Cu-K radiation. The UV-vis spectra were recorded on a Lambda 35 Perkin-Elmer

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spectrometer (Perkin-Elmer, USA). The thermal diffusivities (α) of all composite films were

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measured using a laser flash apparatus (NETZSCH LFA 467 NanoFlash) at 25 °C. The

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composite films were cut into round disks with a diameter of 25.0 mm and square disks with a


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length of 10.0 mm for in-plane and through-plane thermal diffusivities measurements,

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respectively. Each test was repeated five times, and the values with large errors were excluded.

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The TC was calculated using TC=α×ρ×Cp, where ρ is the density of composite papers according

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to ρ = m/V, where m and V are the mass and volume of the samples, respectively; Cp is the

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specific heat capacity obtained by differential scanning calorimetry (Mettler, Switzerland)

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through the sapphire method.21 The original curves to examine in-plane thermal diffusivities

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were presented in Figure S1 and the detailed results (including α, ρ, Cp, TCin-plane, TCthrough-plane,

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etc) were summarized in Table S1. The electrical resistivities of all composite films were

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measured by high-resistance instrument (Shanghai Taiou Electronic Co. Ltd., China).

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Thermogravimetric analysis (TGA) was performed using a PerkinElmer Pyris-1 Thermal

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Analyzer (PE, USA) at a heating rate of 10 °C/min in an air atmosphere. The tensile properties of

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composite films were evaluated at room temperature using a universal testing machine (SANS,

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China) with a speed of 2 mm/min.

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3 RESULTS AND DISCUSSIONS

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3.1 Preparation of GO-BNMPs composite films and mechanical properties. The GO-BNMPs

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composite films were prepared by dispersing BNMPs into the GO aqueous suspension and

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subsequent cast drying, as illustrated in Figure 1. The used GO suspension was obtained by

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dispersing graphite oxide uniformly in water by bath sonication and then stirring. The TEM

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image (Figure 2c) showed that the ultra-thin GO sheet had lateral sizes of several micrometers

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with a wrinkled morphology. Its XPS spectrum clearly presented C 1s and O 1s peaks (Figure


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2a). The C/O ratio determined from XPS data was 2.5, which suggested a high oxidation degree.

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Further, the C 1s spectra of GO sheets can be divided into four peaks of the C=C (284.7 eV), C–

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O (286.2 eV), C–O–C (286.9 eV) and O=C–O (287.8 eV) bonds, which means GO contained

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hydroxyl, epoxide and carbonyl functional groups (Figure 2b).26-27 Owing to the presence of

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various hydrophilic groups, GO is water dispersible and many works have demonstrated that GO

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can easily self-assemble via layer by layer into a free-standing layered films.28-29 The as-received

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BNMPs had lateral sizes of several micrometers and thickness of 270-440 nm (Figure 2d). After

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the BNMPs was incorporated into the GO suspension by sonication and then stirring, the

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obtained homogenous GO-BNMPs aqueous mixtures were poured into a Teflon mold and the

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GO-BNMPs composite films were prepared by drying at 40 oC.

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Figure 1. Schematic illustration of preparation procedure of GO-BNMPs composite films.


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Figure 2. (a, b) XPS spectra and (c) TEM photo of GO and (d) SEM photo of BNMPs.

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As well known, the BNMPs cannot stably disperse in water due to the lack of any polar

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groups. For the BNMPs aqueous suspension obtained by sonication and stirring, almost all the

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BNMPs quickly deposited at the bottom of the tube (red circle) after being statically placed, as

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shown in Figure 3a. Interestingly, when BNMPs were incorporated into the GO suspension, the

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GO-BNMPs mixture could maintain stable dispersion for a long time. As shown in Figure. 3a, no

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apparent deposition phenomenon was observed for the GO-BNMPs suspension after being

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statically placed for 24 h. After centrifuging the GO-BNMPs suspension at 10000 rpm for 10

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min, only a small amount of sediments were observed at the bottom. It is worth noting that the

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sediments could be easily re-dispersed uniformly by intensely shaking and stirring, and there was

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still no sedimentation after being placed for 24 h again (Figure 3b). These results demonstrated


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that it was the existence of GO made the BNMPs form a good dispersion in the aqueous medium.

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To investigate the probable interaction between BNMPs and GO, UV−vis absorbance analysis

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was performed (Figure S2). For the supernatants of BNMPs aqueous dispersions, no absorption

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peak was observed. The result suggested that almost no BNMPs existed in the supernatant,

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which was consistent with our observation that all the BNMPs were precipitated at the bottom of

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the tube. The UV spectrum of pure GO suspension exhibited an absorption peak at 231 nm,

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which was related to the π→π transitions of aromatic C-C bonds.30 For the GO-BNMPs

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suspension, the absorption peak of GO shifted to 233 nm, indicating the presence of relatively

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weak π-π interactions between aromatic regions of GO sheets and basal planes of the BNMPs.

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We believe that the interactions played a positive role for the stable dispersion of BNMPs in the

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GO suspension. On the other hand, it has been reported that the high viscosity of GO suspensions

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could impede the sedimentation of fillers.28 The used GO suspension in this work had a high

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concentration of 5 mg/ml and its relatively high viscosity may be also beneficial to a stable

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dispersion of BNMPs in the GO suspension. When the obtained homogenous GO-BNMPs

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suspension was cast dried, due to good film-forming ability of GO and interactions between GO

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and BNMPs, the GO sheets and basal planes of BNMPs overlapped each other to firstly form a

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compact surface of films at the liquid-air interface during the initial period of drying process; as

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drying went on, the water stream dissipated from the inside of the suspension and the remaining

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GO and BNMPs stacked layer upon layer to obtain the free-standing paper-like composite films.


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Figure 3. Photographs showing (a) BN50 mixture and pristine BNMPs in water after being

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statically placed for 24 h and (b) the BN50 mixture after centrifuging (left) and being placed for

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24 h after the deposited BNMPs re-dispersion (right).

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Using the above cast drying technique, we prepared the GO-BNMPs composite films with

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different BNMPs loadings (Figure 4a). It is found that when the content of BNMPs was not too

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high, for example no more than 50%, the films were intact and smooth. However, further

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increasing the loadings of BNMPs, for example 70%, the obtained film presented fragmentary

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and could not form an integrated film. The typical stress−strain curves of pure GO and GO-

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BNMPs composite films were shown in Figure 4b. For pure GO, due to the existence of

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relatively strong interactions (e.g. π-π interactions, hydrogen bonding, etc.) between the sheets,

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they can easily self-assemble into a free-standing layered film with good mechanical

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performances. Its tensile strength and elongation at the break were 35.0 MPa and 2.8%,


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respectively. When a small amount of BNMPs was incorporated, for example 10%, owing to the

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uniform dispersion of BNMPs in the GO suspensions, the BNMPs would be dispersed in the

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“continuous phase” of GO and its mechanical properties mainly depended on interactions

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between GO sheets. Its tensile strength and elongation at the break of BN10 were 33.8 MPa and

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1.85%, respectively, which was slightly lower than those of GO. When the loading further

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increased, the mechanical properties of composite films were dominated by the interactions

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between GO and BNMPs within a certain loading range. For example, the strength and

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elongation of BN30 were 21.7 MPa and 1.16% while those of BN50 were 21.1 MPa and 0.97%

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respectively. The small difference was because that for the two samples, main interaction to

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influence mechanical properties were both relatively weak interactions between GO and BNMPs.

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It is worth noting that the strength value for sample BN50 (21.1 MPa) was still higher than that

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of commercially available graphite paper (∼10 MPa).31 As shown in Figure 4c,d, BN50

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exhibited excellent flexibility and could be readily folded into the desired shape. The relatively

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high strength and excellent mechanical flexibility were helpful for GO-BNMPs composite films

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to apply in the flexible electronic devices.


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Figure 4. (a) Photographs and (b) stress−strain curves of GO-BNMPs composite films with

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various BNMPs loadings; photographs showing the (c) mechanically flexibility and (d)

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foldability of BN50.

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3.2 Composite films with high in-plane orientation of BNMPs. To explore the alignment of

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BNMPs in the composite films, the surface and cross-section morphologies of BN50 were

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observed by SEM. As shown in Figure 5a-c, the surface of BN50 was intact and basal planes of

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BNMPs were aligned parallel to the surface. The cross-section SEM images (Figure 5d,e)

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showed the inside of composite film had a layer-by-layer structure. The both results suggested a

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high in-plane orientation of BNMPs in the composite films. From the above SEM images and the

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corresponding energy-dispersive X-ray (EDX) results, we also found that BNMPs in the

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composite films still maintained the original lateral sizes and thickness, which suggested that our


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mild sonication treatment (40W, 30 min) was beneficial for the good dispersion of BNMPs but

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cannot destroy or exfoliate BNMPs obviously.

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Figure 5. SEM surface morphology at (a) low and (b) high magnification, (c) EDX results of

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BN50 and cross-section image of BN 50 at (d) low and (e) high magnification.

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In order to further verify the formation of in-plane orientation of BNMPs, the XRD patterns of

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the surface and cross-section of the composite films were recorded. As shown in Figure 6, the

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XRD pattern of pristine BNMPs powder exhibited two characteristic peaks at ~27° (002) and

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~42° (100), corresponding to the signals of in-plane and through-plane, respectively. 6 For the

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composite films, the characteristic peak of GO at ~11° and only one characteristic peak of

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BNMPs at ~27° appeared on the surface-section XRD patterns while the peak at ~42° never

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showed up. Almost the disappearance of through-plane signal indicated BNMPs had a well in-

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plane orientation at the surface. Shen et al reported that the orientation degree of BNMPs in the

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composites can be estimated by comparing the relative intensity (I) of (002) peak to that of (100)

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peak using δ=I(002)/I(100), and the higher value of δ means the better in-plane orientation. 6 For all


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the GO-BNMPs composite films, as almost no (100) peak was detected, the δ value approached

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infinity, which also indicated BNMPs had a well in-plane orientation. We also examined the

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XRD pattern of the cross-section of BN50. As shown in Figure 7, the relative intensity of (100)

4

peak was higher than that of the (002) peak. After calculating by the above δ=I(002)/I(100), the δ

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value was 0.46, which was much less than that of pristine BNMPs with a random morphology

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(41.2). The significantly decreased δ value revealed BNMPs had a high vertical alignment at the

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cross-section6, namely, BNMPs had a high in-plane orientation along the surface.

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Figure 6. The XRD patterns of GO-BNMPs composite films’ surface section.

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Figure 7. The XRD pattern of the cross-section of BN50.

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For comparison, we prepared the PVA/BNMPs(50/50) composite film with 50 wt % BNMPs

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by the analogous casting drying. The XRD pattern of its surface was exhibited in Figure 8. The


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two characteristic peaks of BNMPs at ~27° and ~42° both appeared on the XRD pattern of its

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surface, which meant that BNMPs had a random morphology in PVA/BNMPs composite film.

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Based on the above SEM and XRD results, we concluded that during the formation of composite

4

films, GO can induce BNMPs to preferably align along in-plane orientation.

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Figure 8. XRD pattern of PVA/BNMPs(50/50) composite film’s surface section.

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3.3 Thermal conductivities and electrical properties of composite films. To evaluate the

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effect of the highly oriented structure of BNMPs on thermally conductive properties of GO-

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BNMPs composite films, their in-plane and through-plane thermal conductivities were measured.

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As shown in Figure 9a, the in-plane TC of pure GO was 3.8 W/m·K, which was consistent with

11

previous report12. For GO-BNMPs composites, in-plane TC increased with the fraction of

12

BNMPs. When the loading was 50%, in-plane TC value of BN50 reached 10.3 W/m·K. We also

13

examined the through-plane TCs of composite films (Table S1). The through-plane TC values

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for BN10, BN30 and BN50 were 0.19, 0.26 and 0.38 W/m·K, respectively. The anisotropy index

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(AI), which calculated using AI=TC(in-plane)/TC(through-plane), was 23.1, 24.0 and 27.0 for samples


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BN10, BN30 and BN50, respectively. These high AI values also verified the hierarchical

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alignment structure of composite films.

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The in-plane TC of the above-mentioned PVA/BNMPs(50/50) film was only 3.3 W/m·K,

4

which was much lower than that of BN50 (10.3 W/m·K). The significantly high TC for GO-

5

BNMPs film was related to two factors: firstly, the TC of pristine GO (3.8 W/m·K) was higher

6

than that of PVA (0.6 W/m·K); secondly but more importantly, BN50 had a better in-plane

7

orientation of BNMPs than PVA/BNMPs(50/50) film. To quantitatively illustrate the efficiency

8

of BNMPs in the two system, we calculated the TC increment per wt % BNMPs at BN50 and

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PVA/BNMPs(50/50) using η=(TC-TC0)/50, where TC was the thermal conductivities of the

10

composites and TC0 was that of pure PVA (GO). The former was 0.13 W/m·K while that of the

11

latter was 0.054 W/m·K. The higher TC enhancement efficiency may be related to a better in-

12

plane orientation of BNMPs in GO-BNMPs composite films. As the in-plane TC of GO-BNMPs

13

composite films was not reported in the literatures, we compared our composite films with the

14

reported BNMPs and BNNSs based polymer composite films (Table S2). It is found that in-plane

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TCs of the GO-BNMPs composite films are among the highest values of reported materials at

16

the same fraction of BNMPs or BNNSs.

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The electrical insulation property is another vital factor to be considered when a material is

18

applied in electronic devices. The volume electrical resistivities of GO and GO-BNMPs

19

composite films were measured and shown in Figure 9b. Although the graphite was electrically

20

conductive, the GO exhibited high electrical resistivity of 1.1×109 Ω·cm due to the conjugate


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structure defects on its planes.28 Owing to excellent electrical insulation of BNMPs, the electrical

2

resistivities of GO-BNMPs composites increased significantly with the content of BNMPs. The

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electrical resistivity of BN50 reached 8.0×1010 Ω·cm, which was far beyond the critical

4

resistivity for electrical insulation (1.0×109 Ω·cm). Considering that the GO might be thermally

5

reduced at high temperature, thermal stability properties of our composite films were examined

6

(Figure. S3). The TGA curves showed the GO and composite films had two weight loss

7

processes in an air atmosphere: the first was at 100-250 oC and the second was at 400-550 oC,

8

which corresponded to the loss of oxygen-containing groups and the decomposition of carbon

9

skeleton, respectively. Compared with the GO film, the GO-BNMPs composite films showed

10

improved thermal stability. For example, the temperature at 5% weight loss of BN50 was 204.5

11

o

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thermal stability of GO, which was consistent with the previous study.13 Since that thermal

13

reduction of GO may influence the electrical properties of composite films, we also measured

14

electrical resistivity changes of BN50 under different heat treatment temperature for 6 h (Figure.

15

S4). The results showed that when the temperature was lower than 150 oC, the electrical

16

resistivity of BN50 had no obvious change, which suggested GO was not reduced at lower

17

annealing temperatures. When the treatment temperature was 200 oC, its electrical resistivity

18

slightly decreased to 7×109 Ω·cm, which indicated GO was partially reduced.32,33 When the

19

temperature increased to 250 oC, the electrical resistivity decreased to a value of 2.0×105 Ω·cm

20

and the film was not electrically insulating, which may be ascribed to the further thermal

C, which was 32.1 oC higher than that of GO (172.4 oC). The existence of BN could improve the


17


Page 18 of 26

1

reduction of GO under high temperature. Based on the above results, the high thermally

2

conductive GO-BNMPs composites prepared in this work are more suitable to be used as thermal

3

management materials for relative low-power flexible electronic devices in which no very high

4

temperatures to be undergone.

5 6

Figure 9. (a) In-plane TCs and (b) volume electrical resistivities of GO-BNMPs composite

7

films.

8

4 CONCLUSION

9

In summary, the BNMPs can form a stable dispersion in the aqueous medium with the

10

assistance of GO due to the existence of interactions between GO and BNMPs. Utilizing this

11

homogeneous GO-BNMPs suspension, the free-standing paper-like GO-BNMPs composite films

12

were prepared by a simple cast drying method. The XRD and SEM analysis demonstrated that

13

GO can induce BNMPs to preferably align along in-plane orientation in the composite films. The

14

resultant films possessed a high in-plane TC of 10.3 W/m·K at 50 wt % BNMPs, which was

15

among the highest values of reported BNMPs and BNNSs based polymer composite films. The


18

Page 19 of 26 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


1

films exhibited excellent mechanical flexibility and satisfactory electrical insulation at a

2

temperature of no higher than 200 oC. Compared with the other reported methods to prepare

3

highly in-plane thermally conductive BNMPs based composites, the cast drying method is facile

4

handling, eco-friendly and suitable for large-scale production. Therefore, the GO-BNMPs

5

composite films enable high potential in the flexible electronics applications.

6

ASSOCIATED CONTENT

7

Supporting Information.

8

Figure S1. The in-plane direction signal evolution curves of GO and composite films at

9

different times after pulsed laser heating when the in-plane thermal diffusivities were

10

examined.

11

Figure S2. UV−vis absorbance spectra of GO and GO-BNMPs mixture.

12

Figure S3. The TGA curves of GO, BNMPs and composite films.

13

Figure S4. The electrical resistivity of BN50 after different heat treatment temperatures.

14

Table S1. The density (ρ), specific heat capacity (Cp), thermal diffusivities(α), the

15

calculated thermal conductivities and the anisotropy index (AI) of GO and composite

16

films

17

Table S2. Statistical results of in-plane TCs of BNMPs and BNNSs based film materials

18

published in the literatures

19

AUTHOR INFORMATION


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Page 20 of 26

1

Corresponding Author

2

* Tel.: +86 21 65643735; Fax: +86 21 6564 0293.

3

E-mail addresses: [email protected] (J. Feng)

4

Author Contributions

5

The manuscript was written through contributions of all authors.

6

Notes

7

The authors declare no competing financial interest.

8

ACKNOWLEDGMENT

9

This work was financially supported by the National Natural Science Foundation of China

10

(51373042, 51773040).

11

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SYNOPSIS TOC

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Highly in-Plane Thermally Conductive Composite Films from

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