Coupled chiral structure in graphene-based film for ultrahigh thermal

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Functional Nanostructured Materials (including low-D carbon)

Coupled chiral structure in graphene-based film for ultrahigh thermal conductivity both in-plane and through-plane directions Xin Meng, Hui Pan, Chengling Zhu, Zhixin Chen, Tao Lu, Da Xu, Yao Li, and Shenmin Zhu ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.8b05514 • Publication Date (Web): 11 Jun 2018 Downloaded from http://pubs.acs.org on June 12, 2018

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ACS Applied Materials & Interfaces

Coupled chiral structure in graphene-based film for ultrahigh thermal conductivity both in-plane and through-plane directions Xin Meng,† Hui Pan,† Chengling Zhu,† Zhixin Chen,‡ Tao Lu,† Da Xu, † Yao Li,† and Shenmin Zhu*,† †

State Key Laboratory of Metal Matrix Composites, Shanghai Jiao Tong University, Shanghai 200240, China. ‡

School of Mechanical, Materials & Mechatronics Engineering, University of Wollongong, Wollongong, NSW 2522, Australia.

KEYWORDS graphene film, thermal conductivity, chiral structure, self-assembly, 3D conductive construction

ABSTRACT

The development of high performance thermal management materials to dissipate excessive heat both in-plane and through–plane is of special interest, to maintain efficient operation and prolong the life of electronic devices. Herein, we designed and constructed a graphene-based composite film which contains chiral liquid crystals (cellulose nanocrystals, CNCs) inside graphene oxide

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(GO). The composite film was prepared by annealing and compacting of self-assembled GOCNC which contains chiral smectic liquid crystal structures. The helical arranged nanorods of carbonized CNC acts as in-plane connections which bridge neighboring graphene sheets. More interestingly, the chiral structures also act as through plane connections which bridge the upper and lower graphene layers. As a result, the graphene-based composite film shows extraordinary thermal conductivity, both in-plane (1820.4 W·m-1·K-1) and through-plane (4.596 W·m-1·K-1) directions. As a thermal management material, the heat dissipation and transportation behaviors of the composite film were investigated using a self-heating system and the results showed that the real-time temperature of the heater covered with the film was 44.5 °C lower than a naked heater. The prepared film shows a much higher efficiency of heat transportation than that of the common-used thermal conductive Cu foil. Additionally, this graphene-based composite film exhibits the excellent mechanical strength of 31.6 MPa, and the electrical conductivity of 667.4 S·cm-1. The strategy reported here may open a new avenue to the development of high performance thermal management films.

INTRODUCTION Modern smart and portable electronic devices require high-performance heat dissipaters to maintain their high performance and long lifetime under the operations of high power density. That is why the development of thermal management material is of special importance. As a type of monolayer sp2-hybridized carbon in a 2D honeycomb lattice,1-2 graphene is a promising candidate because of its outstanding theoretical thermal conductivity of K ≈ 5300 W·m-1·K-1.3 Researchers have been engaged in the production of graphene-based films with high thermal dissipations.4-12 Graphene oxide (GO) prepared by Hummers’ method is a scalable and accessible precursor to be applied as building blocks of macroscopic films.13-15 After chemical or


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thermal reduction, the reduced graphene oxide (rGO) films exhibit excellent mechanical, electrical and thermal properties. For example, Shen et al. reported that the rGO film fabricated by the evaporation of GO aqueous dispersion and subsequent thermal treatment exhibited a K of 1100 W·m-1·K-1.8 A filtration and chemical reduction technique was adopted to prepare rGO film and the film showed an improved K of 1390 W·m-1·K-1.9 Although some great progresses have been made in recent years, there is still a huge gap between the macroscopic results and theoretically expected values, which urges researchers to study the intrinsic mechanism and then further promote the thermal performance of graphene films. In graphene or other graphite related films, acoustic phonons - the ion-core lattice vibrations, are believed as the dominant carriers of heat conduction16. Interfaces inside of macroscopic films, including grain boundaries and edges, would strongly scatter the phonons and eventually suppress the transportation of phonons in the macroscopic films. In an rGO film, voids or “air-pockets” formed during thermal annealing of the GO film create macroscopic gaps between the graphene layers.17-18 These defects act as the scattering sites of phonons and strongly degrade the thermal conductivity of the macroscopic film. The chief issue needs to be addressed is to maintain the structural integrity of graphene. That is the reason why large-area graphene oxide (LGO) sheets were used to improve the thermal conductivity, owing to the reduced interface effects.9 The fabrication of LGO can be high in cost and complicated in centrifugation,11 and the mechanical strength of graphene films was inevitably compromised.19 Thus it is necessary to search for some novel routes to connect small graphene sheets and realize an integral graphene film with minimum grain boundaries and edges. Graphene-based films have a pronounced anisotropy in their thermal conductivity.20 The through-plane thermal conductivity is 3-4 orders lower than that of in-plane value,20 due to the


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weak van der Waal’s interaction between graphene layers.21 Researchers attempted to introduce nanofillers to enhance the through-plane thermal conductivity of graphene films.22-26 Carbon nanotubes (CNTs) are the most common additives in graphene-based composites and the addition of CNTs leads to the formation of “pillared-graphene” nanostructure in the composites.27-29 Pan et al. developed rGO-based composite films and observed that the throughplane thermal conductivity experienced an apparent improvement from 0.055 to 0.091 W·m-1·K-1 by the incorporation of CNTs.25 However, the strong mutual van der Waal’s forces of CNTs make them aggregate between the graphene layers, limiting the effectiveness of the CNTs loading on the in-plane thermal performance of the resultant graphene-based film.25-26 It is of great challenge to design a graphene-based film with microstructures suitable for the improvement of thermal conductivity both in-plane and through-plane. The nanostructures of liquid crystals (LCs) give us new inspirations30-32. In contrast to the lack of positional order of a nematic LCs phase, a multilayered structure constructed in a smectic LCs phase presents both orientational and positional orders.33 Typically, a chiral smectic C (SmC*) phase, in which the chiral intercalated molecular orientation n is oriented in a conical helical morphology along the layer normal n0, is a peculiar liquid crystal phase with macroscopic polarization and relevant physical properties. If the unique chiral structures are introduced into graphene layers, the thermal conductivities of both in-plane and trough-plane are expected to be enhanced. Based on this concept, here we designed a chiral structured film through the assembly of cellulose nanocrystal (CNC) into graphene oxide, and then investigated its thermal conductivity. CNC is a typical rod-like cellulose derivative with chiral nematic liquid crystal manner34, which has been utilized not only as the matrix to construct photonic crystal films,35 but also as an reinforcement of graphene-based films in terms of mechanical and electrical


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properties.36-37 In this work, rod-like CNC phases are uniformly dispersed and aligned as helices on the GO sheets and exhibit a chiral smectic arrangement between the layers. After hightemperature annealing, the CNC phase is carbonized into nanorod (CNR) which bridges the boundaries and gaps between graphene layers of in-plane and through-plane. The in-plane and through-plane thermal conductivity of the graphene-based film show a distinct improvement by the introduction of CNC and the subsequent high-temperature annealing process. Accompanied with excellent electrical and mechanical properties, the ultrahigh thermal conductive graphenebased composite film is promising to be applied as an ideal thermal management material.

EXPERIMENTAL SECTION Materials preparation. GO was prepared using the modified Hummers’ method.37-38 During the whole oxidation process, the reactor temperature was kept below 10 °C in order to prevent the destruction of the hexagonal structure and CO2 formation.38 CNC was prepared by an sulfate acid hydrolysis method from cotton as shown in our previous work.39 GO-CNC composite film was fabricated by the evaporation-induced self-assembly (EISA) of the corresponding dispersions on a PET substrate at 25 °C, which typically takes 1-2 days. The composite film was then annealed at different temperatures to reduce the GO and carbonize the CNC. Finally, the composite film was compressed at 300 MPa for 1 h to further improve the density. More detailed synthesis procedures are presented in the supporting information. Microstructure characterization. Zeta potentials of the diluted GO and CNC dispersion (0.01 wt.%) were measured on a Zetasizer Nano ZS (Mastersizer 2000E, Malvern) without adjusting ionic strength. The size and morphologies of GO, CNC and GO-CNC dispersions were observed by atomic force microscopy (AFM, Nanonavi E-Sweep SII). The chirality of the film was


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investigated on a Circular Dichroism spectrometer (CD, J-815 JASCO). Polarized optical microscopy (POM, ZEISS Axio Scope.A1) was carried out to study the liquid crystal performance of the GO-CNC colloids. The morphologies of the film were observed on a SEM (S-4800 Hitachi, 5 kV) and a TEM (JEOL JSM-2100F). TG and DSC analyses were carried out on a differential scanning calorimetry (Netzsch STA449 F3) under Ar atmosphere. XRD patterns were recorded on a Rigaku D/max 2550VL/PC system operated at 35 kV and 200 mA with Cu Kα radiation (λ = 1.5406 Å). XPS spectra were measured on a Perkin-Elmer PHI-5400 spectrometer, using Mg Kα radiation as the excitation source. FT-IR spectra were collected on a Nicolet 6700 spectrometer (Thermo Fisher) and the samples were mixed and pre-compressed with KBr before tests. Raman spectra were collected on a Renishaw Raman microscope with 532 nm radiation. SAXS pattern was obtained on the BL16B1 beamline (beam size ≤ 0.4×0.8 mm, λ = 0.124 nm) at the Shanghai Synchrotron Radiation Facility (SSRF, photon flux ≈ 1×1011). The sample-to-detector distance for SAXS is 2,050 mm; the exposure time was 20 s and the air was used for background collection. A chicken tendon was used for calibration. Performances tests.The thermal conductivity was calculated using the equation: K = α·ρ·Cp

(1)

where K, α, ρ and Cp represent the thermal conductivity (W·m-1·K-1), the thermal diffusivity (mm2·s-1), the density (g·cm-3) and the specific heat capacity (J·g-1·K-1), respectively. The density (ρ) was obtained according to ρ = m·V−1, where m and V were the mass and volume of the sample, respectively. The average thickness of the film was measured on a thickness tester (AICE Inc.) at more than 3 different positions. The specific heat capacity was obtained from differential scanning calorimetry (DSC, Netzsch STA449 F3) at 25 °C. The thermal diffusivity of the graphene-based composite film was determined on a laser flash apparatus (Netzsch, LFA-


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447 NanoFlash) operated at room temperature in a vacuum of 0.01 Pa. The test film was cut into discs of φ =12.7 mm and 25.4 mm for the through-plane and the in-plane tests, respectively. The thermal management performance of the graphene-based film was characterized on a self-heating system equipped with an infrared thermal imaging camera (FLIR, A300). The electrical conductivities were calculated from the measured electrical resistivity on a multifunctional digital standard four-probe instrument (RTS-8). The mechanical properties of the graphene-based film were measured by a tensile test (QJ-210, Shanghai Qingji Testing Instruments Co., LT., China.) with a strain rate of 10 mm·min-1. More details are presented in the supporting information.

Figure 1 Schematic assembly of hierarchical chiral architecture of graphene-based composite film.

RESULTS AND DISCUSSION Structural Characterization. The unique structure of the composite film is constructed using a simple bottom-up selfassembly route which combines 2D GO nanosheets and 1D CNC nanorods, as shown in Figure


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1. Firstly, the GO and CNC dispersions prepared using the modified Hummers’ method38 and an acid hydrolysis method,39 respectively, were mixed together. Then the GO-CNC composite film was fabricated through an evaporation-induced self-assembly (EISA) process on a hydrophobic PET substrate. The dispersion of the CNC nanorods on the graphene layers can be described as below: the nanorods are arranged as their helices parallel to graphene sheets in a direction, say X-axis; in the Z-axis, the chiral spirals of the CNCs between graphene layers do not only prevent the layers stacking but more importantly ensure the connection between the top and bottom layers through chemical bonding. Finally, the high temperature annealing leads to the reduction of the GO and the carbonization of the CNC. The feasibility of self-assembly of GO and CNC in the hybrid colloids is the prerequisite for construction of the GO-CNC hybrid material. As shown in Figure S1, the zeta potentials of the GO and the CNC dispersion are measured as -35.2 and -35.0 mV, respectively, presenting a perfect matching in favor of the subsequent self-assembly. An AFM image of the GO-CNC hybrid colloid is shown in Figure 2(a). The CNC nanorods align as ordered nanostructures on the surface of the GO layers, with a typical helical arrangement rather than individual dispersion. The peculiar observation is resulted from the smectic liquid crystal phases formed in the concentrated GO-CNC colloids.39 The chirality of the GO-CNC is revealed by CD spectra shown in Figure 2(b). In comparison to the CD curve of the GO (black curve in Figure 2(b)) which shows without any peak, the CD curve of the GO-CNC sample (blue curve in Figure 2(b)) exhibits a broad positive peak at 580 nm, attributed to the existence of a left-handed chiral nanostructure in the composite.39-41 The chiral smectic structure of the GO-CNC colloids is further observed in POM images (arrows shown in Figure 2(c)), with a nearly-parallel banded texture. Small-angle X-ray scattering (SAXS) pattern of GO-CNC colloids (Figure 2(d)) exhibits


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a typical rhombus-like symmetry, suggesting a typical structural anisotropy.39 Furthermore, a sharp peak corresponding to 45 nm (d = 2π/q) is shown in the Lorentz transformation pattern (q2I(q) - q profile), ascribed to the (001) plane of layered GO nanostructure.42 Therefore, a selfassembly of GO-CNC has been achieved in the hybrid colloids, which leads to the subsequent fabrication of the composite film.

Figure 2 Characterizations of self-assembly of GO-CNC (weight ratio = 1:1) hybrid colloids: (a) AFM; (b) Circular Dichroism; (c) POM; and (d) SAXS.

The graphene-based composite film was fabricated by evaporation-induced self-assembly (EISA) on a hydrophobic PET substrate. The GO-CNC film has a flat and smooth surface as shown in Figure 3(a). The morphology of the GO-CNC film is presented in Figure 3(b, c). The


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top view SEM image (Figure 3(b)) shows the helical arrangement of the CNC phases on the surface of the GO layers, which is consistent with the AFM observation (Figure 2(b)). Figure 3(c) shows cross section images of the composite film. It can be seen that the CNC nanorods are sandwiched by the GO nanosheets and thus the film presents an ordered sandwich nanostructure. As a comparison, a sample was prepared by directly mixing GO and CNC in aqueous solution. The section image of this prepared film has been presented in Figure S4, in which GO nanosheets exhibit disordered arrangement and CNC nanorods tend to agglomerate between the graphene layers. Therefore, self-assembly method here reported is in favor of forming the nanostructure with oriented graphene layers and uniform CNCs dispersion. The dependence of the film morphologies on the CNC content has also been investigated and the results are presented in Figure S5. It appears that the GO composite film with 50% CNC takes the synergistic advantages of oriented graphene nanostructure and uniform CNCs intercalation and has the most promising morphology among all these samples. Hence, the sample with this optimal relative proportion was chosen for further research. Interestingly, the graphene-based film has a silver color and metallic luster after high temperature annealing and compression (Figure 3(d)), and it also has an excellent flexibility and is able to withstand repeated bending and folding deformations. The morphology of the composite film is well reserved after annealing and compression, as evidenced in Figure 3 (e, f). Similar to GO-CNC before the calcination, the carbonized nanorods in the reduced graphene oxide (rGO-CNR) exhibit helical nanostructures on the graphene planes (Figure 3(e)) and some transformed nanorods were perpendicular to the graphene sheets (Figure 3(f)). The laminated sandwich architecture of the annealed and compacted samples (rGO-CNR-1500) becomes much more compacted than the samples without the heat treatment (pristine GO-CNC). The uniform dispersion of the carbonized CNCs is also


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observed in TEM images (Figure S6(a)), in which the nanorods exhibit high crystallinity with clear lattice fringes (Figure S6(b)). The interplanar spacing was measured to be ~0.34 nm, in accordance with a perfect graphite lattice. It is clear that the CNC was graphitized. The helical structure of the carbonized CNCs bridges the in-plane separated graphene layers, while a 3D carbon network is constructed by the chiral CNC nanorods in conjunction with different vertical reduced graphene oxide sheets. These two structural features have a great effect on the resultant heat transportation performance both in-plane and through-plane directions.

Figure 3 Morphology of GO-CNC (weight ratio = 1:1) and corresponding RGO-CNR films. Photograph of (a) pristine GO-CNC before calcination and compression; (d) rGO-CNR-1500. SEM images of (b) Top view surface of GO-CNC; (c) Side view cross section of GO-CNC; (e) Top view surface of rGO-CNR-1500; (f) Side view cross section of rGO-CNR-1500.

The thermal reduction seems to play a significant role in the thermal performance of the graphene-based film because the scattering sites of phonons such as oxygen contained functional


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groups and non-hexagonal defects can be reduced by the thermal reduction.10 It appears that the annealing temperature is a critically important to achieve a high thermal conductivity. The higher temperature, the better thermal conductivity reaches, but the high annealing temperature increases cost and energy consumption. To determine a suitable annealing temperature, a thermochemistry analysis was carried out under argon atmosphere up to 1500 °C and the results are presented in Figure 4(a). According to the TG curve, the mass loss is differentiated by four stages:43 (I) from room temperature to 150 °C, the water absorbed into the interlayers of the GO was removed;17 (II) from 150 to 250 °C, the decomposition of functional groups in the GO started, in which H2O, CO and CO2 were removed through the dehydration and decarboxylation reactions,44 leading to a sharp decrease in the TG curve; (III) from 250 to 500 °C, further decomposition of the GO involved in the elimination of anhydrides and phenols45 and the CNC phases experienced a pyrolysis process;46 (IV) from 500 to 1500 °C, more stable oxygen contained functional groups in the GO and CNC was gradually removed, with further graphitization,5,

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resulting a subsequent slow weight loss. The DSC result shows a similar

tendency to the TG curve and the sharp peak at ~200 °C is related to the dehydration and decarboxylation reactions and the broad peak from 400 to 500 °C is related to the pyrolysis of the CNC. It is worth noting that there are a number of peaks from 950 to 1300 °C, which is attributed to the further reduction of the RGO.10 After 1300 °C, only 1.3% weight loss is observed in the TG curve (Figure 4 (a)), indicating that 1500 °C is almost high enough to completely reduce the GO and carbonize the CNC layers. Figure 4(b) shows XRD patterns of the graphene-based films before and after the heat treatments at 800 and 1500°C. Before the heat-treatments, the distinct peak at 2θ = 10.7° or d = 8.24 Å corresponds to the d-spacing of (0 0 1)GO. The peaks centered at 2θ = 15.6°, 16.8° and


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22.8° in the GO-CNC sample are due to (11 0) (1 1 0) and (2 0 0) of monoclinic P21 cellulose Iβ, respectively.48 After the heat treatment (at 800 or 1500 °C, red and blue curve in Figure 4(b)), the (0 0 1) GO peak is replaced by a (0 0 2)graphite peak at 2θ =26.3° or d = 3.38 Å. The (0 0 2) peak of the sample annealed at 1500°C is significantly larger than that of the sample annealed at 800°C and thus the degree of graphitization is significantly elevated at the higher annealing temperature, and meanwhile the peaks originated from the cellulose are completely removed by the annealing. It seems that the CNC phase has been completely decomposed and carbonized after the heat treatment. Figure 4(c, d) shows XPS spectra of the graphene-based composites before and after the heat treatments. The C1s spectrum of the GO-CNC film (Figure 4(c)) and rGO-CNR film (Figure 4(d)) can be fitted by three peaks corresponding to C=C/C-C (~285.0 eV), C-O-C/C-OH (~287.0 eV) and C=O/O-C=O (~288.9 eV).17-18, 49 The C/O ratio of the GOCNC film is 1.81, which is reflected by the large area of oxygen containing groups (blue and green curves in Figure 4(c)). In contrast, the oxygen content decreases significantly owing to the reduction and carbonization during the annealing. The relative area of C=C/C-C is enlarged markedly and the integral C/O ratio increases to 15.56. The vast removal of the oxygen contained functional groups was also supported by FT-IR spectroscopy (Figure 4(e)). The characteristic peaks at 1740 cm-1, 1430 cm-1 and 1010 cm-1 in the GO-CNC sample (black curve in Figure 4(e)) are ascribed to the stretching vibrations of C=O, C-OH and C-O-C groups, respectively.5, 18 The annealed rGO-CNR sample exhibits infrared inert to a certain degree like the previous report,43 with the surprising disappearance of oxygen contained groups (red curve in Figure 4(e)). However, the typical peak at 1640 cm-1 related to C=C is still presented after the annealing, attributed to the presence of sp2 graphitic skeleton. The graphitization of the graphene-based composite film was further investigated by Raman spectroscopy (Figure 4(f)). D


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peak at ~1300 cm-1 is related to the disorder and defects, while G peak corresponds to the (0 0 2) crystal plane of graphite. The intensity ratio of D peak and G peak reveals the structural integrity of the graphene film.49-50 The ID/IG ratio of the rGO-CNR film is a little higher than that of the GO-CNC film, which is interpreted by the defects and vacancies in the lateral lattice of graphene generated from the decomposition of oxygen bonded saturated sp3 carbons.17 Nevertheless, the increase of the annealing temperature boosts the restoration of sp2 lattice domains in the graphene-based film, thus the ID/IG ratio decreases from 0.91 of rGO-CNR-800 (red curve in Figure 4(f)) to 0.80 of rGO-CNR-1500 (blue curve in Figure 4(f)) as the annealing temperature increases from 800 to 1500°C. Furthermore, a sharp 2D peak at ~2700 cm-1 is observed in the annealed samples, probing the single layer specific sp2 nanocarbon.50 The Raman spectra (Figure 4(f)) also show that the graphene-based composite film has a high degree of graphitization after the high temperature annealing, which is consistent with the strong graphite (002) peak in the XRD pattern (blue curve in Figure 4(b)).


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Figure 4 Structural characterizations of graphene-based composite films (in which weight ratio of GO and CNC is 1:1) before and after high temperature annealing. (a) TG and DSC curve; (b) XRD patterns; (c, d) XPS C1s analysis of GO-CNC and rGO-CNC, respectively; (e) FT-IR spectrum; (f) Raman spectrum.


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It is reasonable to conclude that the GO-CNC composite film consisting of characteristic chiral liquid crystal structure has been fabricated by self-assembly. The rod-like CNC nanorods arrange in a helical order and connect the isolated graphene layers in in-plane and through-plane directions. After the high temperature annealing and compression, the CNC phases transformed to carbonized nanorods with a high degree of graphitization and the GO sheets experience a complete thermal reduction. Therefore, a 3D thermal conductive architecture is constructed.

Thermal Performances The thermal conductivities of the graphene-based composite film were measured using a laserflash method and the results are shown in Figure 5. The detatiled experimental parameters, including the density, specific heat capacity and thermal diffusivity of graphene-based films, are summarized in Table S1. In this system, the thermal conductivity would be influenced by two key factors: the annealing temperature and the content of the CNC in the composite. As described above, high annealing temperature is beneficial to the thermal conductivity. As shown in Figure 5(a), with the temperature increased from 800 to 1000, 1200, 1500 °C, the thermal conductivities of the composite film in in-plane direction increase from 766.7 to 1064.7, 1475.7 and 1820.4 W·m-1·K-1, respectively. Similar phenomena have been observed in through-plane direction. Both the in-plane and through-plane thermal conductivities experience an ascending tendency with the annealing temperature (Figure 5(a, b)), which can be explained by the removal of lattice defects and oxygen contained functional groups in the rGO and the restoration of sp2 graphene domains. Additionally, the high temperature carbonizes the CNC phase and transforms it from the thermal and electric insulation phase to a conductive carbonized phase (Figure S6(b)). Considering about the efficiency and cost, 1500 °C was chosen for the further investigation. In


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order to find the optimized graphene to CNC ratio, the thermal conductivities of the graphenebased films with various content of the CNC were studied and the results are compared in Figure 5(c, d). The in-plane and the through-plane thermal conductivities reach to their maxima at 1820.4 W·m-1·K-1 and 4.596 W·m-1·K-1 respectively when the CNC content reaches to 50%, which is higher than that of the pure rGO film (1708.8 W·m-1·K-1 in in-plane and 3.992 W·m1

·K-1 in through-plane). It is manifested that the proper content of nanorods is in favor of

thermal properties, but the excessive addition of nanofillers results an undesirable reduction. Much more CNCs would possibly act as scattering sites of phonons, resulting in decrease of thermal conductivities.

Figure 5 Thermal conductivity (TC) of graphene-based hybrid films, all the films experienced a compaction process before tests. (a, b) In-plane and Through-plane TC of films of rGO and rGOCNR (weight ratio = 1:1) films with the variation of temperature, respectively; (c, d) In-plane


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and Through-plane TC of graphene-based films annealed at 1500 °C with the variation of CNC content.

The thermal management properties of the graphene-based composite film were investigated in a self-heating system and the results are shown in Figure 6. In order to simulate the heat dissipation of a practical application, the graphene-based film was covered on a rectangle heating plate and an infrared camera was used to monitor the real-time temperature distribution, as described in the previous literature.6 (Figure 6(a-c) and S7) The heater was charged at a constant voltage of 6 V and current of 0.25 A by a DC power source for the first 5 minutes and then the power was cut off and let the sample naturally cool to room temperature. The temperature change at a fixed point (Point 1 in Figure 6(a)) with operation time is presented in Figure 6(b). The temperature of the heater (black curve in Figure 6(b)) raises rapidly at the beginning of the heating process, followed by a slow rise and finally reaches to about 90 °C before the power off. After the termination of the power, the temperature decreases sharply to room temperature. When the heating plate is covered by a graphene-based film, the heating plate has a similar temperature change but a much slower heating rate and a lower steady temperature (red and blue curve in Fig. 6(b)). The steady temperature of the heating plate covered with the rGO-CNR-1500 film coverage is 45.1 °C, which is 5.3 and 44.5 °C lower than that of the plate covered with the rGO-1500 film coverage and the naked plate, respectively. The thermal diffusions within the graphene-based films under the heating condition were investigated and the temperature distribution of the plate were measured under the steady state of heating procedure (Line 2 in Figure 6(a)), which is shown in Figure 6(c). The heating plate covered by the rGOCNR-1500 film (blue curve in Figure 6(c)) shows a lower temperature distribution than the


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counterparts of the pristine rGO film and the naked plate, which is attributed to its highest thermal conductivity (Figure 5). Therefore, the graphene composite film obtained after the highest temperature annealing exhibits the best heat dissipation performance.

Figure 6 Thermal management performances of graphene-based films. (a-c) Characterization of thermal dissipation: (a) Infrared image of rGO-CNR-1500 film; (b) Temperature – time curve of different graphene-based film measured by the Point 1 in figure (a); (c) Temperature – distance curve of different graphene-based film measured by the Line 2 in figure (a). (d-f) Characterization of thermal transportation: (d) Infrared image of rGO-CNR-1500 film and Al foil; (e) Temperature – time curve of different graphene-based film measured by the Point 1 and 1’ in figure (d); (f) Temperature – distance curve of different graphene-based film measured by the Line 2 and 2’ in figure (d).

Apart from heat dissipation, heat transportation is another practical consideration of thermal management materials. An infrared camera was applied to detect the heat transportation of


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graphene-based strips, the same as reported in literatures11, 51 and the results are shown in Figure 6(d-f) and S8. The graphene-based film was pasted on the heating plate using conductive silver slurry to reduce interfacial thermal resistance. The heating plate was powered at a constant voltage and current of 6 V, 0.65 A. Similar to the investigations of thermal dissipation, the obtained infrared videos and images are shown in Figure 6(d), and the Temperature – Time curve at the fixed points 1 and 1’ in Figure 6(d) are shown in Figure 6(e). The temperature distribution curves in the steady state (Line 2 and 2’ in Figure 6(d)) are shown in Figure 6(f). The thermal transportation performance of a Cu foil (theoretical value of 377 W·m-1·K-1) was used as a reference. It can be seen that slightly higher temperature rise of the graphene based films than the Cu foil in the heating process (blue curve in Figure 6(e,f)). In contrast, the graphene-based composite strips show much more obvious increase of temperature. The rGO-CNR-1500 film exhibits an average heating rate of 1.147 °C·min-1 at first 28 s, higher than the slopes of the rGO1500 film (0.954 °C·min-1) and Cu foil (0.037 °C·min-1), respectively. The steady-state temperature of the composite film is 4.0 °C higher than that of the pristine rGO film. The excellent heat transportation performance is consistent with their thermal conductivity results (Figure 5). On the other hand, the temperature distribution (Figure 6(f)) exhibit a more complicated vibration tendency, which can be devided into two regions: (I) the region close to the heater, where heat dissipation is the main mechanism so the composite film shows a lower temperature, coincident with the observation in Figure 6(b,c); (II) the region far from the heater, where heat transportation is dominant so the composite film shows a higher temperature, similar to the trend in Figure 6(e). Therefore, the graphene-based composite films exhibit extraordinary thermal management performances, including heat dissipation and transportation, which are


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resulted from the remarkable thermal conductivities both in in-plane and through-plane directions.

Mechanical and Electrical Properties In addition to superior thermal conductivity, excellent mechanical and electrical properties are also the pursuits of researchers to further broaden the practical applications of graphene-based films. CNC is a rod-like cellulose derivative with excellent mechanical strength,52-53 which is considered as an ideal reinforcement of graphene-based films.36-37 The assembled 2D-1D nacrelike nanostructures are beneficial to the mechanical properties of graphene-based films, by the introduction of highly wrinkled nanostructure37 and the formation of hydrogen bonds between GO and CNC phases.39 The tensile stress-strain curves of the graphene-based films are presented in Figure 7(a), and the detailed results are summarized in Table S2. The as-prepared GO-CNC composite film (red curve in Figure 7(a)) exhibits a tensile strength of 217.6 MPa, which is higher than that of the pure GO film (181.3 MPa, shown in black curve in Figure 7(a)). After the annealing, the rGO-CNR film (cyan curve in Figure 7(a)) still has the tensile strength of 31.6 MPa, much higher than that of pure rGO film (14.3 MPa, blue curve in Fig. 7(a)). This result can be explained by the carbonization of the CNC phase in the composite and the carbonized CNC acts as the reinforcement in the obtained graphene-based films.


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Figure 7 Mechanical and electrical properties of graphene-based composite films: (a) tensile stress-strain curves; (b) electrical conductivity.

Similar to thermal conductivity (Figure 5(a)), the electrical conductivity is also promoted by the increase of the annealing temperature and the introduction of the CNC phase (Figure 7(b)). The electrical conductivity of graphene-based composite films reaches up to 667.4 S·cm-1 after the 1500 °C annealing and compaction, which is much higher than that of the pristine rGO films (329.6 S·cm-1). Although the carriers of electrical conduction are electrons, not the phonons, the removal of the oxygen functional groups and the restoration of graphene sp2 domains lead to the reduction of electrons scattering and thus improve the electrical conductivity of macroscopic films54. In addition, the carbonized CNC phase bridges the adjacent graphene layers, forming a 3D conductive network not only for thermal but also for electrical transport. That is to say, the mechanical and electrical properties of the graphene-based films can be enhanced by the selfassembly of GO-CNC nanostructures and subsequent annealing, further expanding their potential applications. As compared with others reported (Table S3), the mechanical and electrical properties of the film in this work is competitive.


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Mechanism of thermal conductive graphene-based film In graphene-based materials, heat conduction is carried by acoustic phonons38, which are vulnerable to be scattered by lattice defects and boundaries.45 Ballistic-diffusive transportation is the basic mechanism of graphene-contained materials.55 For a perfect graphene crystal without any impurity, void, interface and gap, the thermal conductivity is controlled by intrinsic scattering of crystal anharmonicity and shows “ballistic” mechanism without diffusion to other directions.16 However, the phonons are strongly scattered by extrinsic sites in real materials, such as isotopes, substrates, voids and boundaries55 and these defects reduce heat conduction varies of specific directions. The introduction of nanofillers seems to be a creative method since the defects such as boundaries and gaps appears to be repaired by the nanofillers via the mechanism of “molecule welding”.18 The sizes, nanostructures and chemical properties of the nanofillers should be carefully considered to avoid the aggregation in the matrix and construct a highefficient conductive architecture. CNC is an ideal nanofiller for the graphene-based films because of its intrinsic low aspect ratio and uniform dispersion between the graphene layers. Furthermore, CNC is able to be selfassembled within the GO in aqueous colloids, and chiral smectic liquid crystal properties can be achieved in the resultant films.39 (Figure 2(c,d) and 3(b,c)) After the annealing and compaction process, the CNC phase transformed to CNR (arrows in Figure 3(e,f)), but the helical arrangement between the graphene sheets is maintained (Figure 3(e,f)). The scheme of the fabricated 3D thermal conductive construction is shown in Fig. 8. The model is similar to the “pillared-graphene” composed of graphene skeleton and incorporated CNTs,27-29 but the arrangement of the CNR nanofillers in this work play a crucial role in the promotion of thermal conductivity. The chirality introduced is used to construct the unique structure through the liquid


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crystal formation in GO-CNC composite. After carbonization, the typical structure is preserved in the resultant film. The in-plane and through-plane thermal conductivity of the graphene-based composite film can be improved, ascribed to the introduction of the carbonized CNC phases which arranged as a chiral manner. As shown in SEM image in Figure 3(e), the carbonized helical CNC nanostructures are covered on the surface of graphene layers and reconnect the boundaries and interfaces of the graphene sheets (Figure 8(b)); on the other hand, the carbonized nanorods fill the gaps and bridge the graphene layers (Figure 8(c)) and form through-plane thermal conductive paths as shown in Figure 3(f). Therefore, the established 3D thermal conductive network is established, leading to the improvement of the thermal conductivity of the macroscopic films.

Figure 8 Schematic illustration of graphene-based composite films with 3D hierarchical thermal conductive network: (a) Integral rGO-CNR composite film; (b) the scheme of the thermal conductive network in in-plane direction; (c) the scheme of the thermal conductive network in through-plane direction.


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The simple preparation and ultrahigh thermal performance of the graphene-based composite film in this work surpasses the previous works reported in literatures (Table 1). Compared with the pure graphene films,4-12 the rGO-CNR composite film of this work exhibits competitive or even higher in-plane thermal conductivity. It is suggested that the rod-like carbonized CNCs are helically arranged in the composite film and this arrangement reconnects the boundaries of graphene sheets, resulting in the outstanding heat transportation in the in-plane direction. Although CNTs are the most common nanofillers applied in graphene-based materials, the unavoidable agglomeration attributed to the strong van der Waal’s force is the main factor which prevents the further addition of CNTs and the improvement of resultant properties.25-26 According to the previous work,26 the optimum content of CNTs is limited to 15%. Harsh methods such as sonication and ball milling are expected to further disperse CNTs on graphene sheets. However, the inevitable damage to the graphene and reinforcement may cause undesirable loss of performances. In contrast, a milder self-assembly process is applied to achieve the dispersion of rod-like carbon nanofillers on graphene sheets and the optimum content of the CNCs is at about 50%. From table 1, we notice that a high through-plane thermal conductivity was achieved in the graphene composite paper reported by Zhang et al.22 However, the carbon nanorings were grown on graphene sheets by a complex in-situ CVD method. More importantly, no report in previous work can realize the increase of thermal conductivity both in in-plane and through-plane direction. The rGO-CNR films here reported solve the problem by the chiral arrangement and achieve remarkable thermal properties in both in-plane and throughplane directions, providing a great potential in practical thermal conductive applications.

Table 1 Thermal conductivity (TC) of the works in reported literatures and this work.


25


Reference

Teng, C.4

Xin, G.6

Materials

Fabrication

Exfoliated

Ball milling + Filtration +

Graphene

Annealing

film

Compaction (30 MPa)

rGO film

Testing

Thickness

TC∥a

TC⊥b

methods

(µm)

(W·m-1·K-1)

(W·m-1·K-1)

Self-heating

30

1529

-

-

1434

-

7.5

1390

-

9

826.0

-

10

1940

-

40

977

-

-

890

5.81

56

804.24

0.061

49

1388.7

0.164

36

1820.4

4.596

°C)

+

method

Electro-spray

deposition

+

Self-heating

Roll-to-roll

process

+

method

(2850

Page 26 of 32

Annealing (2850 °C) Kumar, P.9

Huang, Y.10

rLGO film

rGO film

Filtration + Reduction (HI, 80

Laser-flash

°C)

method

EISA + Annealing (2800 °C)

Laser-flash method

Peng, L.11

Kong, Q.43

Zhang, J.22

EISA + Annealing (3000 °C)

Laser-flash

+ Compaction (300 MPa)

method

rGO-CF

Filtration + Annealing (1000

Laser-flash

film

°C)

method

Graphene-

In-situ growth of Carbon

Laser-flash

Carbon

nanorings (800 °C, 100 s)

method

rGO-CNT


Laser-flash

paper

°C, CNT content: 5%)

method

rGO-CNT


Laser-flash

paper

°C, CNT content: 15%)

method

rGO-CNR

EISA

film

Annealing

rGO film

nanorings paper Pan, T.25

Lu, H.26

This work

(self-assembly) (1500

°C)

+

Laser-flash

+

method

Compaction (300 MPa) a

In-plane TC; b Through-plane TC

CONCLUSION


26

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In summary, graphene-based composite films with ultrahigh thermal conductivity both in inplane and through-plane have been prepared by the evaporation-induced self-assembly of GOCNC film, and the subsequent high-temperature annealing and compaction. The assembled GOCNC composite films show typical chiral smectic structures, which are maintained in the annealed and compacted samples. The prepared graphene-based composite films exhibit outstanding thermal conductivity in two directions, with the highest in-plane K of 1820.4 W·m1

·K-1 and the highest through-plane K of 4.596 W·m-1·K-1. The optimized addition of the CNCs

can be reached as high as 50% and have positive effect on the resultant thermal properties of the macroscopic films. The superior thermal conductivity of the composite film is attributed to the 3D thermal conductive network, in which carbonized nanorods with helical arrangement effectively connect the adjacent graphene layers both in the in-plane and the through-plane direction. Therefore, the graphene composite film shows an extraordinary thermal management performance in terms of heat dissipation and heat transportation. The heating plate covered by the prepared film thus experiences a significant temperature reduction of 44.5 °C compared with the naked plate and the film exhibits a high heat transportation rate of 1.147 °C·min-1. The typical laminated nanostructures also lead to the improvement of the mechanical and electrical properties and provide a bright prospect to graphene-based films in the industries such as heat dissipation, heat transportation and electric heating. ASSOCIATED CONTENT Supporting Information. Details of experimental sections are provided in Supporting Information S1. Zeta potential, POM and AFM images of GO and CNC colloids are shown in Figures S1-S3. SEM and TEM images of rGO-CNR composites are shown in Figures S4-S6. The performances of thermal management are shown in Figures S7-S8. Details of thermal and


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mechanical properties of graphene films are supplied in Table S1-S2. Electrical conductivity (EC) and tensile strength of the works in reported literatures and this work are summarized in Table S3. AUTHOR INFORMATION Corresponding Author *E-mail: [email protected] Author Contributions The manuscript was written through contributions of all authors. All authors have given approval to the final version of the manuscript. Funding Sources This work was supported by National Key R&D Program of China [2016YFA0202900], National Science Foundation of China [51672173], Shanghai Science and Technology committee [17JC1400700], Science and Technology Planning Project of Guangdong Province [2016A010103018]. The authors gratefully acknowledge the Shanghai Synchrotron Radiation Facility (SSRF) and Shanghai LEVSON Group Co., Ltd. for the measurements. ACKNOWLEDGMENT The authors gratefully acknowledge the Shanghai Synchrotron Radiation Facility (SSRF) for the measurements. REFERENCES (1) Geim, A. K.; Novoselov, K. S. The Rise of Graphene. Nat. Mater. 2007, 6 (3), 183-191, DOI: 10.1038/nmat1849. (2) Li, D.; Mueller, M. B.; Gilje, S.; Kaner, R. B.; Wallace, G. G. Processable Aqueous Dispersions of Graphene Nanosheets. Nat. Nanotechnol. 2008, 3 (2), 101-105, DOI: 10.1038/nnano.2007.451. (3) Balandin, A. A.; Ghosh, S.; Bao, W.; Calizo, I.; Teweldebrhan, D.; Miao, F.; Lau, C. N. Superior Thermal Conductivity of Single-Layer Graphene. Nano Lett. 2008, 8 (3), 902-907, DOI: 10.1021/nl0731872.


28

Page 29 of 32 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


(4) Liu, Z.; Li, Z.; Xu, Z.; Xia, Z. X.; Hu, X. Z.; Kou, L.; Peng, L.; Wei, Y. Y.; Gao, C. WetSpun Continuous Graphene Films. Chem. Mater. 2014, 26 (23), 6786-6795, DOI: 10.1021/cm5033089. (5) Song, N. J.; Chen, C. M.; Lu, C. X.; Liu, Z.; Kong, Q. Q.; Cai, R. Thermally Reduced Graphene Oxide Films as Flexible Lateral Heat Spreaders. J. Mater. Chem. A 2014, 2 (39), 16563-16568, DOI: 10.1039/c4ta02693d. (6) Xin, G. Q.; Sun, H. T.; Hu, T.; Fard, H. R.; Sun, X.; Koratkar, N.; Borca-Tasciuc, T.; Lian, J. Large-Area Freestanding Graphene Paper for Superior Thermal Management. Adv. Mater. 2014, 26 (26), 4521-4526, DOI: 10.1002/adma.201400951. (7) Liu, L.; Bian, X. M.; Tang, J.; Xu, H.; Hou, Z. L.; Song, W. L. Exceptional Electrical and Thermal Transport Properties in Tunable All-Graphene Papers. RSC Adv. 2015, 5 (92), 7523975247, DOI: 10.1039/c5ra15533a. (8) Shen, B.; Zhai, W. T.; Zheng, W. G. Ultrathin Flexible Graphene Film: An Excellent Thermal Conducting Material with Efficient EMI Shielding. Adv. Funct. Mater. 2014, 24 (28), 4542-4548, DOI: 10.1002/adfm.201400079. (9) Kumar, P.; Shahzad, F.; Yu, S.; Hong, S. M.; Kim, Y. H.; Koo, C. M. Large-Area Reduced Graphene Oxide Thin Film with Excellent Thermal Conductivity and Electromagnetic Interference Shielding Effectiveness. Carbon 2015, 94, 494-500, DOI: 10.1016/j.carbon.2015.07.032. (10) Huang, Y. L.; Gong, Q. M.; Zhang, Q.; Shao, Y.; Wang, J. J.; Jiang, Y. Q.; Zhao, M.; Zhuang, D. M.; Liang, J. Fabrication and Molecular Dynamics Analyses of Highly Thermal Conductive Reduced Graphene Oxide Films at Ultra-High Temperatures. Nanoscale 2017, 9 (6), 2340-2347, DOI: 10.1039/c6nr06653d. (11) Peng, L.; Xu, Z.; Liu, Z.; Guo, Y.; Li, P.; Gao, C. Ultrahigh Thermal Conductive yet Superflexible Graphene Films. Adv. Mater. 2017, 29 (27), 1700589, DOI: 10.1002/adma.201700589. (12) Teng, C.; Xie, D.; Wang, J. F.; Yang, Z.; Ren, G. Y.; Zhu, Y. Ultrahigh Conductive Graphene Paper Based on Ball-Milling Exfoliated Graphene. Adv. Funct. Mater. 2017, 27 (20), 1700240, DOI: 10.1002/adfm.201700240. (13) Xu, Y.; Bai, H.; Lu, G.; Li, C.; Shi, G. Flexible Graphene Films via the Filtration of WaterSoluble Noncovalent Functionalized Graphene Sheets. J. Am. Chem. Soc. 2008, 130 (18), 58565857, DOI: 10.1021/ja800745y. (14) Lin, X.; Shen, X.; Zheng, Q.; Yousefi, N.; Ye, L.; Mai, Y. W.; Kim, J. K. Fabrication of Highly-Aligned, Conductive, and Strong Graphene Papers Using Ultra large Graphene Oxide Sheets. ACS Nano 2012, 6 (12), 10708-10719, DOI: 10.1021/nn303904z. (15) Dikin, D. A.; Stankovich, S.; Zimney, E. J.; Piner, R. D.; Dommett, G. H. B.; Evmenenko, G.; Nguyen, S. T.; Ruoff, R. S. Preparation and Characterization of Graphene Oxide Paper. Nature 2007, 448 (7152), 457-460, DOI: 10.1038/nature06016. (16) Balandin, A. A. Thermal Properties of Graphene and Nanostructured Carbon Materials. Nat. Mater. 2011, 10 (8), 569-581, DOI: 10.1038/nmat3064. (17) Chen, C. M.; Huang, J. Q.; Zhang, Q.; Gong, W. Z.; Yang, Q. H.; Wang, M. Z.; Yang, Y. G. Annealing a Graphene Oxide Film to Produce a Free Standing High Conductive Graphene Film. Carbon 2012, 50 (2), 659-667, DOI: 10.1016/j.carbon.2011.09.022. (18) Li, H. L.; Dai, S. C.; Miao, J.; Wu, X.; Chandrasekharan, N.; Qiu, H. X.; Yang, J. H. Enhanced Thermal Conductivity of Graphene/Polyimide Hybrid Film via a Novel "Molecular Welding" Strategy. Carbon 2018, 126, 319-327, DOI: 10.1016/j.carbon.2017.10.044.


29


Page 30 of 32

(19) Xin, G. Q.; Yao, T. K.; Sun, H. T.; Scott, S. M.; Shao, D. L.; Wang, G. K.; Lian, J. Highly Thermally Conductive and Mechanically Strong Graphene Fibers. Science 2015, 349 (6252), 1083-1087, DOI: 10.1126/science.aaa6502. (20) Renteria, J. D.; Ramirez, S.; Malekpour, H.; Alonso, B.; Centeno, A.; Zurutuza, A.; Cocemasov, A. I.; Nika, D. L.; Balandin, A. A. Strongly Anisotropic Thermal Conductivity of Free-Standing Reduced Graphene Oxide Films Annealed at High Temperature. Adv. Funct. Mater. 2015, 25 (29), 4664-4672, DOI: 10.1002/adfm.201501429. (21) Inagaki, M.; Kaburagi, Y.; Hishiyama, Y. Thermal Management Material: Graphite. Adv. Eng. Mater. 2014, 16 (5), 494-506, DOI: 10.1002/adem.201300418. (22) Zhang, J. W.; Shi, G.; Jiang, C.; Ju, S.; Jiang, D. Z. 3D Bridged Carbon Nanoring/Graphene Hybrid Paper as a High-Performance Lateral Heat Spreader. Small 2015, 11 (46), 6197-6204, DOI: 10.1002/smll.201501878. (23) Hsieh, C. T.; Lee, C. E.; Chen, Y. F.; Chang, J. K.; Teng, H. S. Thermal Conductivity from Hierarchical Heat Sinks Using Carbon Nanotubes and Graphene Nanosheets. Nanoscale 2015, 7 (44), 18663-18670, DOI: 10.1039/c5nr04993h. (24) Hsieh, C. T.; Chen, Y. F.; Lee, C. E.; Chiang, Y. M.; Teng, H. S. Thermal Transport in Stereo Carbon Framework Using Graphite Nanospheres and Graphene Nanosheets. Carbon 2016, 106, 132-141, DOI: 10.1016/j.carbon.2016.04.082. (25) Pan, T. W.; Kuo, W. S.; Tai, N. H. Tailoring Anisotropic Thermal Properties of Reduced Graphene Oxide/Multi-Walled Carbon Nanotube Hybrid Composite Films. Compos. Sci. Technol. 2017, 151, 44-51, DOI: 10.1016/j.compscitech.2017.07.015. (26) Lu, H. F.; Zhang, J.; Luo, J.; Gong, W. B.; Li, C. W.; Li, Q. L.; Zhang, K.; Hu, M.; Yao, Y. G. Enhanced Thermal Conductivity of Free-Standing. 3D Hierarchical Carbon NanotubeGraphene Hybrid Paper. Composites, Part A 2017, 102, 1-8, DOI: 10.1016/j.compositesa.2017.07.021. (27) Varshney, V.; Patnaik, S. S.; Roy, A. K.; Froudakis, G.; Farmer, B. L. Modeling of Thermal Transport in Pillared-Graphene Architectures. ACS Nano 2010, 4 (2), 1153-1161, DOI: 10.1021/nn901341r. (28) Xu, L.; Wei, N.; Zheng, Y.; Fan, Z.; Wang, H. Q.; Zheng, J. C. Graphene-Nanotube 3D Networks: Intriguing Thermal and Mechanical Properties. J. Mater. Chem. 2012, 22 (4), 14351444, DOI: 10.1039/c1jm13799a. (29) Chen, J.; Walther, J. H.; Koumoutsakos, P. Covalently Bonded Graphene-Carbon Nanotube Hybrid for High-Performance Thermal Interfaces. Advanced Functional Materials 2015, 25 (48), 7539-7545, DOI: 10.1002/adfm.201501593. (30) Sodemura, T.; Kubo, S.; Higuchi, H.; Kikuchi, H.; Nakagawa, M. Unimodal Nematic Liquid Crystalline Random Copolymers Designed for Accepting Chiral Dopants. Bull. Chem. Soc. Jpn. 2017, 90 (2), 216-222, DOI: 10.1246/bcsj.20160343. (31) Sawada, T.; Serizawa, T. Filamentous Viruses as Building Blocks for Hierarchical SelfAssembly toward Functional Soft Materials. Bull. Chem. Soc. Jpn. 2018, 91 (3), 455-466, DOI: 10.1246/bcsj.20170428. (32) Kowalski, B. A.; Guin, T. C.; Auguste, A. D.; Godman, N. P.; White, T. J. Pixelated Polymers: Directed Self Assembly of Liquid Crystalline Polymer Networks. ACS Macro Lett. 2017, 6 (4), 436-441, DOI: 10.1021/acsmacrolett.7b00116. (33) Ueda, H.; Akita, T.; Uchida, Y.; Kimura, T. Room-Temperature Magnetoelectric Effect in a Chiral Smectic Liquid Crystal. Appl. Phys. Lett. 2017, 111 (26), DOI: 10.1063/1.5007317.


30

Page 31 of 32 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


(34) Kelly, J. A.; Giese, M.; Shopsowitz, K. E.; Hamad, W. Y.; MacLachlan, M. J. The Development of Chiral Nematic Mesoporous Materials. Acc. Chem. Res. 2014, 47 (4), 10881096, DOI: 10.1021/ar400243m. (35) Giese, M.; Blusch, L. K.; Khan, M. K.; MacLachlan, M. J. Functional Materials from Cellulose-Derived Liquid-Crystal Templates. Angew. Chem. Int. Ed. 2015, 54 (10), 2888-2910, DOI: 10.1002/anie.201407141. (36) Xiong, R.; Hu, K. S.; Grant, A. M.; Ma, R. L.; Xu, W. N.; Lu, C. H.; Zhang, X. X.; Tsukruk, V. V. Ultrarobust Transparent Cellulose Nanocrystal-Graphene Membranes with High Electrical Conductivity. Adv. Mater. 2016, 28 (7), 1501-1509, DOI: 10.1002/adma.201504438. (37) Wen, Y. Y.; Wu, M. M.; Zhang, M.; Li, C.; Shi, G. Q. Topological Design of Ultrastrong and Highly Conductive Graphene Films. Adv. Mater. 2017, 29 (41), 1702831, DOI: 10.1002/adma.201702831. (38) Eigler, S.; Enzelberger-Heim, M.; Grimm, S.; Hofmann, P.; Kroener, W.; Geworski, A.; Dotzer, C.; Roeckert, M.; Xiao, J.; Papp, C.; Lytken, O.; Steinrueck, H. P.; Mueller, P.; Hirsch, A. Wet Chemical Synthesis of Graphene. Adv. Mater. 2013, 25 (26), 3583-3587, DOI: 10.1002/adma.201300155. (39) Pan, H.; Zhu, C.; Lu, T.; Lin, J.; Ma, J.; Zhang, D.; Zhu, S. A Chiral Smectic Structure Assembled from Nanosheets and Nanorods. Chem. Commun. 2017, 53 (11), 1860-1863, DOI: 10.1039/c6cc08337d. (40) Therien-Aubin, H.; Lukach, A.; Pitch, N.; Kumacheva, E. Coassembly of Nanorods and Nanospheres in Suspensions and in Stratified Films. Angew. Chem. Int. Ed. 2015, 54 (19), 56185622, DOI: 10.1002/anie.201500277. (41) Lagerwall, J. P. F.; Schutz, C.; Salajkova, M.; Noh, J.; Park, J. H.; Scalia, G.; Bergstrom, L. Cellulose Nanocrystal-Based Materials: From Liquid Crystal Self-Assembly and Glass Formation to Multifunctional Thin Films. NPG Asia Mater. 2014, 6, e80, DOI: 10.1038/am.2013.69. (42) Xu, Z.; Gao, C. Graphene Chiral Liquid Crystals and Macroscopic Assembled Fibres. Nature Communications 2011, 2, 571-579, DOI: 10.1038/ncomms1583. (43) Kong, Q. Q.; Liu, Z.; Gao, J. G.; Chen, C. M.; Zhang, Q.; Zhou, G. M.; Tao, Z. C.; Zhang, X. H.; Wang, M. Z.; Li, F.; Cai, R. Hierarchical Graphene-Carbon Fiber Composite Paper as a Flexible Lateral Heat Spreader. Adv. Funct. Mater. 2014, 24 (27), 4222-4228, DOI: 10.1002/adfm.201304144. (44) Lv, W.; Tang, D. M.; He, Y. B.; You, C. H.; Shi, Z. Q.; Chen, X. C.; Chen, C. M.; Hou, P. X.; Liu, C.; Yang, Q. H. Low-Temperature Exfoliated Graphenes: Vacuum-Promoted Exfoliation and Electrochemical Energy Storage. ACS Nano 2009, 3 (11), 3730-3736, DOI: 10.1021/nn900933u. (45) Menéndez, J. A.; Phillips, J.; Xia, B.; Radovic, L. R. On the Modification and Characterization of Chemical Surface Properties of Activated Carbon: In the Search of Carbons with Stable Basic Properties. Langmuir 1996, 12 (18), 4404-4410, DOI: 10.1021/la9602022. (46) Shopsowitz, K. E.; Hamad, W. Y.; MacLachlan, M. J. Chiral Nematic Mesoporous Carbon Derived From Nanocrystalline Cellulose. Angew. Chem. Int. Ed. 2011, 50 (46), 10991-10995, DOI: 10.1002/anie.201105479. (47) Zhu, Y. W.; Murali, S.; Cai, W. W.; Li, X. S.; Suk, J. W.; Potts, J. R.; Ruoff, R. S. Graphene and Graphene Oxide: Synthesis, Properties, and Applications. Adv. Mater. 2010, 22 (35), 39063924, DOI: 10.1002/adma.201001068.


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(48) Nishiyama, Y.; Langan, P.; Chanzy, H. Crystal Structure and Hydrogen-Bonding System in Cellulose 1 Beta from Synchrotron X-Ray and Neutron Fiber Diffraction. J. Am. Chem. Soc. 2002, 124 (31), 9074-9082, DOI: 10.1021/ja0257319. (49) Yang, D.; Velamakanni, A.; Bozoklu, G.; Park, S.; Stoller, M.; Piner, R. D.; Stankovich, S.; Jung, I.; Field, D. A.; Ventrice, C. A.; Ruoff, R. S. Chemical Analysis of Graphene Oxide Films after Heat and Chemical Treatments by X-Ray Photoelectron and Micro-Raman Spectroscopy. Carbon 2009, 47 (1), 145-152, DOI: https://doi.org/10.1016/j.carbon.2008.09.045. (50) Dresselhaus, M. S.; Jorio, A.; Hofmann, M.; Dresselhaus, G.; Saito, R. Perspectives on Carbon Nanotubes and Graphene Raman Spectroscopy. Nano Lett. 2010, 10 (3), 751-758, DOI: 10.1021/nl904286r. (51) Ding, J.; Zhao, H.; Wang, Q.; Dou, H.; Chen, H.; Yu, H. An Ultrahigh Thermal Conductive Graphene Flexible Paper. Nanoscale 2017, 9 (43), 16871-16878, DOI: 10.1039/c7nr06667h. (52) Wang, B.; Walther, A. Self-Assembled, Iridescent, Crustacean-Mimetic Nanocomposites with Tailored Periodicity and Layered Cuticular Structure. ACS Nano 2015, 9 (11), 1063710646, DOI: 10.1021/acsnano.5b05074. (53) Song, W.; Liu, D.; Prempeh, N.; Song, R. Fiber Alignment and Liquid Crystal Orientation of Cellulose Nanocrystals in the Electrospun Nanofibrous Mats. Biomacromolecules 2017, 18 (10), 3273-3279, DOI: 10.1021/acs.biomac.7b00927. (54) Chen, H.; Mueller, M. B.; Gilmore, K. J.; Wallace, G. G.; Li, D. Mechanically Strong, Electrically Conductive, and Biocompatible Graphene Paper. Adv. Mater. 2008, 20 (18), 35573561, DOI: 10.1002/adma.200800757. (55) Xu, Y.; Li, Z. Y.; Duan, W. H. Thermal and Thermoelectric Properties of Graphene. Small 2014, 10 (11), 2182-2199, DOI: 10.1002/smll.201303701.

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Coupled chiral structure in graphene-based film for ultrahigh thermal

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