Flexible Films for Smart Thermal Management: Influence of Structure

Subscriber access provided by BUFFALO STATE

Applications of Polymer, Composite, and Coating Materials

Flexible Films for Smart Thermal Management: Influence of Structure Construction of Two-dimensional Graphene Network on Active Heat Dissipation Response Behavior Siqi Cui, Fang Jiang, Na Song, Liyi Shi, and Peng Ding ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.9b10538 • Publication Date (Web): 29 Jul 2019 Downloaded from pubs.acs.org on July 29, 2019

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 20 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

ACS Applied Materials & Interfaces

Flexible Films for Smart Thermal Management: Influence of Structure Construction of Two-dimensional Graphene Network on Active Heat Dissipation Response Behavior Siqi Cui,†,‡ Fang Jiang,†,‡ Na Song,‡ Liyi Shi,‡ and Peng Ding*,†,‡ †School

of Materials Science and Engineering, Shanghai University, Shanghai 200444, China

‡Research

Center of Nanoscience and Nanotechnology, Shanghai University, Shanghai 200444,

China

1

ACS Paragon Plus Environment

ACS Applied Materials & Interfaces 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

ABSTRACT ：In recent years, development and wide application of microelectronic technology brings forward high demands to active thermal management systems. However, such systems are not only costly, but also usually tethered, and need constant power to operate. To avoid such limitation, smart thermal management systems have been developed to achieve active thermal management. Here, inspired by temperature control principle of butterfly, shape memory polymer was used to endow thermally conductive graphene-polymer hybrid film with intelligent. As the device reaches 60 °C, the bud shaped hybrid film started to bloom, which is a visual active heat dissipation process. As a result, this active process promoted the thermal management capacity of the hybrid film and increased the temperature-raising time of light-emitting diode (LED). Through the construction of bilayer structure, the transmission channel for phonon transfer was optimized, which lead the hybrid film to a remarkable thermal conductivity of 21.83 W·m-1·K-1 with 30 wt% graphene. This graphene-polymer hybrid film shows potential application in smart thermal management field.

KEYWORDS: smart thermal management, thermal conductivity, shape memory polymer, hybrid film, graphene

2


Page 2 of 20

Page 3 of 20 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. INTRODUCTION Thermal management system is one of the important components which ensure the safety and reliability of devices. With the rapid development of aerospace, national defense military industry, microelectronics, solar energy, light-emitting diode (LED), et al., miniaturization and ultra-high integration of device multiply the calorific value per unit area. This situation raises higher requirements for thermal management system.1-3 In thermal management system, on the one hand, the heat dissipation/thermal conductivity of materials is required to improve continuously. At the same time, they should also exhibit other excellent comprehensive performances such as light weight, good mechanical properties et al. These requirements make thermally conductive polymer-based composites become an ideal choice in thermal management systems. Constructing thermally conductive pathway in polymer by high thermal conductivity fillers has been extensively studied and frequently used to improve thermally conductive property of polymers.4-9 Feng et al. reported a hybrid film, with thermally conductive pathway consisting of silver nanoparticles (2.0 vol %), achieves a high thermal conductivity of 6.0 W·m-1·K-1.10 In thermally conductive fillers, two-dimensional nanomaterials with graphene as representative, exhibit excellent heat transfer performance, which could endow polymer materials with high thermal conductivity enhancement.11-14 For example, Yu et al. obtained a epoxy composite with thermal conductivity of 6.57 W·m-1·K-1.15 This high thermal conductivity could be contributed to vertically aligned thermally conductance network composed by graphene sheets. And due to the contribution of two-dimentional thermally conductive pathway composed by graphene, poly(vinylidene fluoride) composite (graphene, 60 wt%) exhibits a high thermal conductivity of 41.64 W·m-1·K-1.16 However, it’s still a challenge to obtain polymer-based composites with thermal conductivity above 10 W·m-1·K-1 at filler contents less than 50.0 wt %.17 Nevertheless, thermal management systems are usually tethered which constant need power to operate. In several application fields, they need to be freestanding and couldn’t be connected with external power. This means that, the application mode and situation of the systems are significant limited. To solve this issue, inspired by temperature control principle of scales of butterfly, smart thermal management systems are developed to achieve active thermal management. One feasible solution is to endow the thermal management material with

3



Page 4 of 20

intelligence.18 It is believed that such smart thermal management materials should have the capacity to sense their surroundings and produce thermal dissipation respond accordingly. And a useful method is to use stimuli-responsive materials, which take advantage of energy provided by stimulus

from

environment

to

execute

a

homologous

action.19-21

Therefore,

using

stimuli-responsive materials to endow thermally conductive materials with intelligent is a promising candidate to fabricate smart thermal management materials. Here, a novel graphene-polymer hybrid film was fabricated by evaporation-induced self-assembly progress for smart thermal management. Through the design of bilayer structure and construction of two-dimensional thermally conductive network, the graphene-polymer hybrid film exhibits high thermal conductivity of 21.83 W·m-1·K-1 with 30 wt% graphene. In addition, taking advantage of the stimuli-responsive property of shape memory polymer, the hybrid film is able to transform its shape as the temperature above a certain point, which shows intelligence. Combined this two points, the hybrid film could play a positive role in thermal management of device. As device reaches a certain temperature, it could present a visual representation which is an active thermal dissipation process. 2. EXPERIMENTAL SECTION 2.1. Fabrication of G/PEG/NFC hybrid films. Figure 1a and 2a illustrates the preparation processes of G/PEG/NFC hybrid films. Here, two kinds of hybrid films were prepared, one is uniform hybrid films (U-G/PEG/NFC) and the other is bilayer hybrid films (B-G/PEG/NFC). In order to prepare the U-G/PEG/NFC hybrid films, first moderate amounts of Nanofibrillated Cellulose (NFC) (Guilin Qihongkeji, China) dispersion (Figure S1f, g, Table S1) and polyethylene glycol (PEG) (10000 g/mol, Aladdin, China) were dispersed into deionized water at ordinary temperature with strongly agitation for 0.5 hour, respectively. Then, mixed them these two suspensions together with strongly agitation for 0.5 hour. In this suspension, the PEG and NFC weight ratio is 50:50. A variety of graphene nanosheets (G) (size: ~10 μm, number of layers: ~8; Figure S1a, b)

(LEVSON, China) were added in a controlled manner to suspensions mentioned

above at ordinary temperature and then strongly agitated for about 1 hour to yield a uniform dispersion with graphene nanosheets

content of 0 to 30 wt% (Figure S2a). Next, the dispersions

were poured into a polystyrene dish and dried in oven at 50 °C. Then peel the hybrid film off from 4


Page 5 of 20 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


dish. The hybrid films with G/PEG/NFC weight ratio of 0:50:50, 20:40:40, 25:37.5:37.5 and 30:35:35 were named PEG/NFC, U-G/PEG/NFC-20, U-G/PEG/NFC-25 and U-G/PEG/NFC-30, respectively. The thicknesses of hybrid films were ranged from 40 to 50 μm. As for B-G/PEG/NFC hybrid films, dispersion A (Figure S2b) was first prepared by mixing moderate amounts of NFC and PEG aqueous dispersions with strongly agitation at ordinary temperature for about 1 hour. In dispersion A, the weight ratio of PEG and NFC is 50:50. Likewise, dispersion B (Figure S2b) was prepared by mixing moderate amounts of NFC aqueous dispersions, PEG aqueous dispersions and graphene nanosheets powders with strongly agitation at ordinary temperature for about 1 hour. In dispersion B, the weight ratio of G, PEG and NFC is 50:25:25. Then a moderate amount of dispersion B was poured into a polystyrene dish and dried in oven at 50 °C. After dispersion B was drained, dispersion A was added in this polystyrene dish carefully and dried in oven at 50 °C. Then peel the hybrid film off from dish. And the contents of graphene nanosheets in the B-G/PEG/NFC hybrid films were controlled by the volume ratio of dispersion A and B. The hybrid films with G/PEG/NFC weight ratio of 20:40:40, 25:37.5:37.5 and 30:35:35 were named B-G/PEG/NFC-20, B-G/PEG/NFC-25 and B-G/PEG/NFC-30, respectively. The thicknesses of hybrid films were ranged from 40 to 50 μm. 2.2. Characterizations. The Fourier transform infrared (FTIR) spectra were obtained on FTIR spectrometer (Avatar 370, Nicolet, USA) using potassium bromide pellets. All of the samples were dried at 40 °C overnight under vacuum before the FTIR analysis. The morphology and microstructures of hybrid films were examined by an emission scanning electron microscope (JSM-7500F, JEOL, Japan). The thermal conductivity, λ, can be calculated with the following formula: λ = ρ × Cp × α, where ρ is the mass density, Cp is the specific heat and α is the thermal diffusivity of sample. The in-plane thermal diffusivities of all samples were measured using by a laser flash apparatus (Netzsch LFA 447 Nanoflash, Germany) using “in-plane” mode at 25 °C. Disk with diameter of 25.4 mm, punched out from as-prepared hybrid film, was putted in a special sample holder (Figure S3), which sends the thermal energy along the sample, for this measurement. The position of light energy input and temperature rise measurement are on different sides of samples and in different lateral positions. The latter ensures that the measured rising temperature of sample corresponds to the thermal diffusivity alone in-plane direction.22, 23

5



Concrete details of the mechanism and methodology of the measurements are summarized in Supporting Information. Each thermal diffusivity test was repeated six times, and the values with

large errors were excluded. The densities were measured using a density balance (JA3003J, SOPTOP, China). The heat transport properties of hybrid films were characterized by IR thermal imaging spectrometer (OPTRIS, PI400, Germany). The specific heats were obtained by differential scanning calorimetry (DSC, Netzsch DSC-404C, Germany) at ordinary temperature. The mechanical properties were obtained using a universal tensile tester (Instron 5569A, USA) with a film tension mode at ordinary temperature. Rectangular strips of 5×50 mm with varying thickness were cut from the hybrid films. 3. RESULTS AND DISCUSSION

Figure 1. a) Schematic illustration of the evaporation-induced self-assembly process of U-G/PEG/NFC hybrid film. The SEM images of the b) surface view and c, d) cross-sectional view of U-G/PEG/NFC-30 hybrid film. e) Thermal conductivities of U-G/PEG/NFC and B-G/PEG/NFC hybrid films. f) Comparison of the values of thermal conductivities of B-G/PEG/NFC hybrid films with different composites.

In order to endow materials with ability of smart thermal management, intellectualization of thermally conductive materials is a feasible approach. In this way, the materials could play the role of thermal management to devices. Meanwhile, they could sense their surroundings and produce thermal dissipation respond accordingly. In the aspect of thermally conductive polymer-based composites, we have done a series of works in recent years. And it has been found that, in composites, construction of thermally conductive pathway is a key point to obtain high

6


Page 6 of 20

Page 7 of 20 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


thermal conductivity.12, 17, 24 For hybrid films, one useful method to construct efficient thermally conductive pathway is to build well-ordered hierarchical structure with two-dimensional thermally conductive fillers.25 In this structure, highly ordered aligned two-dimensional thermally conductive fillers could provide smooth channels for impactful phonon transfer. Besides, the thermal conductivity of matrix is very low at ordinary temperature. In hybrid films, phonons transfer thermal energy in strictly two-dimensional pathway with the obstacle from through-plane being avoided. Therefore, the final lateral heat transfer capacity of two-dimensional thermally conductive fillers is expressed to a great degree. In our previous research, hierarchical structure was built by hot pressing process, which exhibit improved thermal conductivity.26 Furthermore, through optimization of the hierarchical structure, the thermal conductivities of hybrid films were further improved.27, 28 Based on this, hierarchical structure (Figure 1b-d), formed by well aligned graphene nanosheets (Figure 1c and d arrows), was used to endow hybrid film with high thermal conductivity. During the evaporation-induced self-assembly progress of U-G/PEG/NFC hybrid film, the evaporation of water elevated graphene nanosheets concentration in mixture, which issued a remarkable enhance in sheet-to-sheet interactions. The nanosheets were then induced to align in the ever-increasing precipitate, thus obtaining a well-defined hierarchical structure. With this structure, U-G/PEG/NFC hybrid film exhibits in-plane thermal conductivity of 16.65 W·m-1·K-1 with 30 wt% content of graphene (Figure 1e), which is 553% higher than that of matrix hybrid film (thermal conductivity of PEG/NFC is 2.55 W·m-1·K-1 at 25°C).

7



Figure 2. a) Schematic illustration of the evaporation-induced self-assembly process of U-G/PEG/NFC hybrid films. The SEM images of surface of b) thermally conductive layer and c) matrix layer of B-G/PEG/NFC-30 hybrid film. The SEM images of cross-sectional view of d) boundary bilayer, e, f) thermally conductive layer and g) matrix layer of B-G/PEG/NFC-30 hybrid film.

With the development of various fields, the requirement of thermal conductivity of materials is improved continuously. Increasing the addition of thermally conductive fillers is a normal method to further improve thermal conductivities of composites. Nevertheless, experimental results indicated that the addition of graphene could significantly improve thermal conductivity of hybrid film, but evidently deteriorate its mechanical property (Table S2, Figure S4) simultaneously. Note that mechanical property is an important point for the application of hybrid film. In order to further improve thermal conductivity of hybrid film without increase its content of graphene, a kind of hybrid film with bilayer structure (B-G/PEG/NFC) was designed, and fabricated by evaporation-induced self-assembly (Figure 2a). This designed bilayer structure consists of matrix layer and thermally conductive layer. The boundary of the two layers could be easily found from the cross-sectional SEM image (Figure 2d). Here, the matrix layer of B-G/PEG/NFC hybrid film has the same content with PEG/NFC hybrid film, which shows similar microstructure with PEG/NFC hybrid film’s (Figure 2c, g, Figure S5a, Figure S6). Like U-G/PEG/NFC hybrid films, thermally conductive layer of B-G/PEG/NFC hybrid films are composed of graphene nanosheets and matrix PEG/NFC. In there, graphene nanosheets aligned along in-plane direction (Figure 2b, Figure S5b) and formed hierarchical structure (Figure 2e, f arrows), which contribute to thermal conductivity of hybrid film.

8


Page 8 of 20

Page 9 of 20 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


With this kind of structure, compared to U-G/PEG/NFC hybrid films, the thermal conductivity of B-G/PEG/NFC hybrid films are further improved with the same contents of graphene nanosheets (Figure 1e). At 30 wt% content of graphene, the in-plane thermal conductivity of B-G/PEG/NFC hybrid film reaches 21.83 W·m-1·K-1, which is 31.11% higher than that of U-G/PEG/NFC-30 hybrid film. It mainly because of the content of graphene in thermally conductive layer of B-G/PEG/NFC hybrid films is increased to 50 wt%, which enables fillers tightly packed to provide more efficient thermally conductive pathway. Meanwhile, matrix layer could endow hybrid film with excellent mechanical performances. Thus, without enhancing the total content of graphene in hybrid film, it could reserves other excellent performances of matrix and further increases thermal conductivity of graphene-polymer hybrid film. Figure 1f and Table S3 summarize thermal conductivities of polymer-based composites in previous literatures.17, 29-36 One can see that, compared with other published works, thermal conductivity of B-G/PEG/NFC hybrid films are at a high level with similar content of fillers. Consequently, it further illustrates that this kind of bilayer structure is effective for the improvement of thermal conductivities of hybrid films. And, some published studies could also prove that.37, 38 Many published studies have reported flexible graphene-polymer hybrid films with high thermal conductivities.7,

16, 39

And these materials show good application potential as thermal

management materials in many fields. However, with the development of microelectronic technology, many application modes and situations have changed. These passive heat dissipation materials are no longer adequate to the demand. Novel smart thermal management materials with active heat dissipation capabilities are expected. For smart thermal management hybrid films, with the exception of thermally conductive properties, intellectualization is another vital point. Here, thermally activated shape memory polymers (SMP) was chosen to endow hybrid films with intelligent. Its temporary shape could be fixed by transfiguring the material above transformation temperature (glass transition temperature or melting temperature) and cooling down.19, 40, 41 As the temperature is higher than transformation temperature again, it could recover the permanent shape without outside force. This particular shape contrivable performance imparts SMPs extensive potential application in varieties of areas such as sensor, aerospace42-45 et al, which also show potential in smart thermal management materials.

9



Figure 3. Shape memory behaviors of the hybrid films. Photographs of PEG/NFC, U-G/PEG/NFC-30 and B-G/PEG/NFC-30 hybrid films with a-c) flower shapes, d-f) temporary bud shapes and g-i) after reverting to the original flower shapes. j) Demonstration of the shape recovery processes of PEG/NFC (I), U-G/PEG/NFC-30 (II) and B-G/PEG/NFC-30 (III) hybrid films at 70 °C in oven. k) Infrared thermal images of shape recovery processes of U-G/PEG/NFC-30 and B-G/PEG/NFC-30 hybrid films on heating stage.

In these hybrid films, thermally activated SMP PEG/NFC was used as matrix to endow thermally conductive hybrid films with intelligent. Here, PEG plays a dominant role in their shape memory properties. Pure PEG film would liquidize at 70 °C (Figure S7e). Due to the present of NFC network46 and the hydrogen bonding between PEG and NFC47, 48 (Figure S8b), hybrid films keep their shape stable and have no leakage of PEG at that temperature (Figure S7). The diameter of the NFC varied over the range of 20-50 nm (Figure S1b, Table S1) and had a large aspect ratio, which was significant for the formation of a continuous network. Based on this, NFC endows hybrid films with excellent flexibility (Figure S4, Table S2) which do benefit to their shape memory property. The shape memory property of the hybrid films were qualitatively exhibited by using flower-shaped films (Figure 3a-c). Above transformation temperature (melting temperature of PEG), these hybrid films were folded into bud shapes (Figure 3d-f) as a temporary shape and fixed by cooling down to ordinary temperature. While the PEG/NFC flower automatically

10


Page 10 of 20

Page 11 of 20 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


bloomed to their original shape (Figure 3j-I) for 40 second after sitting in drying oven of 70 °C, which was due to the transition from temporary shape to permanent shape. After the addition of graphene nanosheets, the response time of hybrid film (U-G/PEG/NFC-30) decreased to 28 second (Figure 3j-II). As the thermal conductivity of hybrid films have been further improved by structure design, the response time of B-G/PEG/NFC-30 hybrid film further reduced to half of U-G/PEG/NFC-30 hybrid film’s (Figure 3j-III), simultaneously. (Due to the better mechanical properties of matrix layer PEG/NFC (Figure S4, Table S2), in this test, matrix layer of B-G/PEG/NFC-30 hybrid film was on the outside of the bud shape hybrid films, and thermally conductive layer on the inside of the bud shape hybrid films.) This result, to some extent, could be attributed to the higher thermal conductivity of B-G/PEG/NFC-30 hybrid film.49 As the heat source was changed to heating stage, the hybrid films kept their bud shape at lower temperature (Figure 3k). With the further increase of the temperature of the heating stage, the flowers also did sharp reaction (Figure 3k). That is to say, in the local heating case, the composite still exhibits good shape memory performance. The rapid respond process of these samples reveals their potential application in smart thermal management.

11



Figure 4. a) Infrared thermal images and physical images of the LED device with different types of G/PEG/NFC hybrid films as lateral heat spreaders. b) Time-temperature relationships of center of LED (3W) with unfolded and folded B-G/PEG/NFC hybrid films as lateral heat spreaders. c) The time difference to reach the same temperature between vacant LED and LED with unfolded and folded B-G/PEG/NFC hybrid films as lateral heat spreaders. d) Time-temperature relationships of center of LED (3W) with different types of G/PEG/NFC hybrid films as lateral heat spreaders. e) The time difference to reach the same temperature between vacant LED and LED with different types of G/PEG/NFC hybrid films as lateral heat spreaders.

12


Page 12 of 20

Page 13 of 20 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


After being intelligent, thermally conductive G/PEG/NFC hybrid films were used for smart thermal management of LED system (Figure S9). In this LED system, hybrid films with bud shape (Figure 3e, f) were packed on the back of LED. The effect of thermal management could be reflected by the temperatures of LED, which were recorded by IR thermal imaging spectrometer (Figure S9). The brighter the color, the higher the temperature. And it can be found from Figure 4a and Figure S10 that, with the increase of time, the temperature of LED increases gradually. However, it is difficult to find the difference of temperature for LED with/without hybrid films as lateral heat spreaders from the figure alone. The time-temperature relationships of LED (Figure 4b, d and Figure S11) are used to show that difference. The results show that G/PEG/NFC hybrid films do have the smart thermal management effect on LED. And the effects could be summarized into the following two aspects. First, as shown in the temperature-time relationships of the center of LED device (Figure 4d, Figure S11), the G/PEG/NFC hybrid films show evident cooling performance. One hand, the temperatures of the center of LED with hybrid films are obvious lower than vacant LED (Figure 4d, S2). Compared to vacant LED, with the hybrid film as lateral heat spreaders, the LED spends more time to reach same temperature (Figure 4d). What’s more, with the increase of temperature, that difference becomes even larger (Figure 4e). Meanwhile, that difference of B-G/PEG/NFC hybrid film is more obvious than U-G/PEG/NFC hybrid film. For another, the times to reach the highest temperatures are delayed obviously (Figure 4d). With B-G/PEG/NFC hybrid film as heat spreader, the times of LED to reach the highest temperature is delayed for 7 second, which is 3 second larger than that of U-G/PEG/NFC hybrid film. That is, B-G/PEG/NFC hybrid film exhibits better heat dissipation effect than U-G/PEG/NFC hybrid film. And similar situation could also be found in the temperature-time relationships of different power and different part of LED (Figure S10, S11). Second, as the temperature of LED reached 60 °C, bud shaped B-G/PEG/NFC hybrid film started to bloom. The visual representation of hybrid film shows an active thermal dissipation process (Figure 4a and d, Figure S10 and S11). In this system, when this blooming process was prevented, the cooling effect of the B-G/PEG/NFC hybrid film is worse than that of the unfolded B-G/PEG/NFC hybrid film. Although, compared to vacant LED, with the folded B-G/PEG/NFC hybrid films as lateral heat spreaders, the LED also spends more time to reach same temperature

13



(Figure 4b). However, with the increase of temperature, this difference doesn’t become even larger (Figure 4c). Above all, as the temperature above 60 °C, this difference shows a down trend with the increase of temperature (Figure 4c). Meanwhile, it doesn’t delays the time to reach the highest temperature (Figure 4b). That reveals the blooming process could play an accelerated role in the heat dissipation capability of hybrid films. Moreover, as the excessive temperature would significantly shorten the life of LED, this phenomenon could also be a visual display of the excessive temperature of LED. From these two points, it can be proved that this B-G/PEG/NFC hybrid film shows the capacity for smart thermal management. However, the reason for not reducing the highest temperature of LED is the mismatching of the heat dissipation capability of hybrid films and the power of LED. And this can be fixed by enhancing the size and quantity of the hybrid film. Combined with the two points above, the G/PEG/NFC hybrid film could be considered as a candidate for smart thermal management. While it’s just an original prototype, the thermally conductive composites with shape memory properties open a new avenue in many fields for smart thermal management. 4. CONCLUSIONS In summary, via a facile evaporation-induced self-assembly process, a shape memory graphene-polymer hybrid film was designed with outstanding thermally conductive properties for smart thermal management. As the device reaches a certain temperature, closed hybrid films start to bloom. The visual representation of hybrid films shows an active thermal dissipation process. Meanwhile, the hybrid films also show evident cooling effect on device. Through the construction of bilayer structure, the hybrid film (B-G/PEG/NFC) exhibits remarkable thermal conductivity of 21.83 W·m-1·K-1 with the graphene content of 30 wt%. Thermally activated shape memory polymer was chosen as matrix to endow hybrid films with intelligent. In combination with such properties, this graphene-polymer hybrid film shows the potential application in smart thermal management field. This study paves a new direction for thermal management based on smart thermally conductive composites.

ASSOCIATED CONTENT Supporting Information

14


Page 14 of 20

Page 15 of 20 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


Mechanical properties of hybrid films; Stress-strain curves of hybrid films; The SEM images of matrix layer surface and thermally conductive layer surface of B-G/PEG/NFC-30 hybrid film; The SEM images of the surface and cross-section of PEG/NFC hybrid film; Thermal conductivities of polymer-based composites in previous literatures; The digital image of PEG film, PEG/NFC hybrid film, U-G/PEG/NFC-30 hybrid film and B-G/PEG/NFC-30 hybrid film at room temperature and 70 °C; FTIR spectra of U-G/PEG/NFC hybrid films, graphene nanoplatelets, NFC/PEG hybrid film and NFC substrate; Schematic of the LED testing system with thermally conductive hybrid films as the heat spreader; Infrared thermal images and physical images of different power (5 W and 10 W) of LED with different types of G/PEG/NFC hybrid films as lateral heat spreaders; Schematic of the LED; Temperature-time relationships at different part of LED (3W, 5W and 10W) with different types of G/PEG/NFC hybrid films as lateral heat spreaders; The time differences to reach the same temperature between vacant LED and LED with G/PEG/NFC hybrid films as lateral heat spreaders.

AUTHOR INFORMATION Corresponding Author *Email: [email protected] Notes The authors declare no competing financial interest.

ACKNOWLEDGMENTS This work was financially supported by the Program of Shanghai Academic/Technology Research Leader (No. 17XD1424400), the National Natural Science Foundation of China (No. 51703122), the Development Fund for Shanghai Talents (No.2017014). The authors thank Dr. Yanyan Lou from Laboratory for Microstructures, Shanghai University, for help with the SEM measurements. The authors are grateful to Prof. Dehong Li, Engr. Jianhai Zhi, and Associate Prof. Xuefei Wang from Ningbo Institute of Material Technology & Engineering, Chinese Academy of Sciences, for help in the mechanical property test.

15



REFERENCES (1) Balandin, A. A. Thermal Properties of Graphene and Nanostructured Carbon Materials. Nat. Mater. 2011, 10, 569-581. (2) Yan, Z.; Liu, G.; Khan, J. M.; Balandin, A. A. Graphene Quilts for Thermal Management of High-Power GaN Transistors. Nat. Commun. 2012, 3, 827-834. (3) Monteverde, F.; Scatteia, L. Resistance to Thermal Shock and to Oxidation of Metal Diborides-SiC Ceramics for Aerospace Application. J. Am. Ceram. Soc. 2007, 90, 1130-1138. (4) Shtein, M.; Nadiv, R.; Buzaglo, M.; Kahil, K.; Regev, O. Thermally Conductive Graphene-Polymer Composites: Size, Percolation, and Synergy Effects. Chem. Mater. 2015, 27, 2100-2106. (5) Cui, X.; Ding, P.; Zhuang, N.; Shi, L.; Song, N.; Tang, S. Thermal Conductive and Mechanical properties of Polymeric Composites Based on Solution-Exfoliated Boron Nitride and Graphene Nanosheets: A Morphology-Promoted Synergistic Effect. ACS Appl. Mater. Interfaces 2015, 7, 19068-19075. (6) Guo, Y.; Xu, G.; Yang, X.; Ruan, K.; Ma, T.; Zhang, Q.; Gu, J.; Wu, Y.; Hu, L.; Guo, Z. Significantly Enhanced and Precisely Modeled Thermal Conductivity in Polyimide Nanocomposites by Chemically Modified Graphene via in-situ Polymerization and Electrospinning-Hot Press Technology. J. Mater. Chem. C 2018, 6, 3004-3015. (7) Huangfu, Y.; Liang, C.; Han, Y.; Qiu, H.; Song, P.; Wang, L.; Kong, J.; Gu, J. Fabrication and Investigation on the Fe3O4/Thermally Annealed Graphene Aerogel/Epoxy Electromagnetic Interference Shielding Nanocomposites. Compos. Sci. Technol. 2019, 169, 70-75. (8) Guo, Y.; Lyu, Z.; Yang, X.; Lu, Y.; Ruan, K.; Wu, Y.; Kong, J.; Gu, J. Enhanced Thermal Conductivities and Decreased Thermal Resistances of Functionalized Boron Nitride/Polyimide Composites. Compos. Part B-Eng. 2019, 164, 732-739. (9) Jiang, F.; Cui, S.; Song, N.; Shi, L.; Ding, P. Hydrogen Bond Regulated Boron Nitride Network Structures for Improved Thermal Conductive Property of Polyamide-imide Composites. ACS Appl. Mater. Interfaces 2018, 10, 16812-16821. (10) Shen, Z.; Feng, J. Highly Thermally Conductive Composite Films Based on Nanofibrillated Cellulose in Situ Coated with a Small Amount of Silver Nanoparticles. ACS Appl. Mater. Interfaces 2018, 10, 24193-24200. (11) Fan, Z.; Gong, F.; Nguyen, S. T.; Duong, H. M. Advanced Multifunctional Graphene Aerogel – Poly (methyl methacrylate) Composites: Experiments and Modeling. Carbon 2015, 81, 396-404. (12) Chen, J.; Huang, X.; Sun, B.; Jiang, P. Highly Thermally Conductive Yet Electrically Insulating Polymer/Boron Nitride Nanosheets Nanocomposite Films for Improved Thermal Management Capability. ACS Nano 2018, 13, 337–345. (13) Gu, J.; Lv, Z.; Wu, Y.; Guo, Y.; Tian, L.; Qiu, H.; Li, W.; Zhang, Q. Dielectric Thermally Conductive Boron Nitride/Polyimide Composites with Outstanding Thermal Stabilities via in-situ Polymerization-Electrospinning-Hot Press Method. Compos. Part A Appl. Sci. Manuf. 2017, 94, 209-216. (14) Han, J.; Du, G.; Gao, W.; Bai, H. An Anisotropically High Thermal Conductive Boron Nitride/Epoxy Composite Based on Nacre-Mimetic 3D Network. Adv. Funct. Mater. 2019, 29, 1900412-1900420. (15) Li, X.-H.; Liu, P.; Li, X.; An, F.; Min, P.; Liao, K.-N.; Yu, Z.-Z. Vertically Aligned, Ultralight

16


Page 16 of 20

Page 17 of 20 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


and Highly Compressive All-Graphitized Graphene Aerogels for Highly Thermally Conductive Polymer Composites. Carbon 2018, 140, 624-633. (16) Hu, T.; Song, Y.; Di, J.; Xie, D.; Teng, C. Highly Thermally Conductive Layered Polymer Composite From Solvent-Exfoliated Pristine Graphene. Carbon 2018, 140, 596-602. (17) Zeng, X.; Sun, J.; Yao, Y.; Sun, R.; Xu, J. B.; Wong, C. P. A Combination of Boron Nitride Nanotubes and Cellulose Nanofibers for the Preparation of a Nanocomposite with High Thermal Conductivity. ACS Nano 2017, 11, 5167-5178. (18) Zhang, X.; Chen, L.; Lim, K. H.; Gonuguntla, S.; Lim, K. W.; Pranantyo, D.; Yong, W. P.; Yam, W. J. T.; Low, Z.; Teo, W. J.; Nien, H. P.; Loh, Q. W.; Soh, S. The Pathway to Intelligence: Using Stimuli-Responsive Materials as Building Blocks for Constructing Smart and Functional Systems. Adv. Mater. 2019, 31, 1804540-1804540. (19) Lendlein, A.; Kelch, S. Shape-Memory Polymers. Angew. Chem. Int. Ed. 2005, 33, 1-9. (20) Liu, C.; Qin, H.; Mather, P. T. Review of Progress in Shape-Memory Polymers. J. Mater. Chem. 2007, 17, 1543-1558. (21) Rabani, G.; Luftmann, H.; Kraft, A. Synthesis and Characterization of Two Shape-Memory Polymers Containing Short Aramid Hard Segments and Poly(ε-caprolactone) Soft Segments. Polymer 2006, 47, 4251-4260. (22) Goli, P.; Ning, H.; Li, X.; Lu, C. Y.; Balandin, A. A. Thermal Properties of Graphene-Copper-Graphene Heterogeneous Films. Nano Lett. 2014, 14, 1497-1503. (23) Yang, X.; Liang, C.; Ma, T.; Guo, Y.; Kong, J.; Gu, J.; Chen, M.; Zhu, J. A Review on Thermally Conductive Polymeric Composites: Classification, Measurement, Model and Equations, Mechanism and Fabrication Methods. Adv. Compos. Hybrid Mater. 2018, 1, 207-230. (24) Lian, G.; Tuan, C.-C.; Li, L.; Jiao, S.; Wang, Q.; Moon, K.-S.; Cui, D.; Wong, C.-P. Vertically Aligned and Interconnected Graphene Networks for High Thermal Conductivity of Epoxy Composites with Ultralow Loading. Chem. Mater. 2016, 28, 6096-6104. (25) Kong, Q.-Q.; Liu, Z.; Gao, J.-G.; Chen, C.-M.; Zhang, Q.; Zhou, G.; 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, 4222-4228. (26) Song, N.; Yang, J.; Ding, P.; Tang, S.; Shi, L. Effect of Polymer Modifier Chain Length on Thermal Conductive Property of Polyamide 6/Graphene Nanocomposites. Compos. Part A Appl. Sci. Manuf. 2015, 73, 232-241. (27) Song, N.; Jiao, D.; Ding, P.; Cui, S.; Tang, S.; Shi, L. Anisotropic Thermally Conductive Flexible Films Based on Nanofibrillated Cellulose and Aligned Graphene Nanosheets. J. Mater. Chem. C 2016, 4, 305-314. (28) Song, N.; Jiao, D. J.; Cui, S.; Hou, X.; Ding, P.; Shi, L. Highly Anisotropic Thermal Conductivity of Layer-by-layer Assembled Nanofibrillated Cellulose/Graphene Nanosheets Hybrid Films for Thermal Management. ACS Appl. Mater. Interfaces 2017, 9, 2924-2932. (29) Pan, G.; Yao, Y.; Zeng, X.; Sun, J.; Hu, J.; Sun, R.; Xu, J. B.; Wong, C. P. Learning from Natural Nacre: Constructing Layered Polymer Composites with High Thermal Conductivity. ACS Appl. Mater. Interfaces 2017, 9, 33001-33010. (30) Tsai, M. H.; Tseng, I.; Chiang, J. C.; Li, J. J. Flexible Polyimide Films Hybrid with Functionalized Boron Nitride and Graphene Oxide Simultaneously to Improve Thermal Conduction and Dimensional Stability. ACS Appl. Mater. Interfaces 2014, 6, 8639-8645. (31) Wang, H.; Tazebay, A. S.; Yang, G.; Lin, H. T.; Choi, W.; Yu, C. Highly Deformable Thermal

17



Interface Materials Enabled by Covalently-Bonded Carbon Nanotubes. Carbon 2016, 106, 152-157. (32) Kumar, P.; Yu, S.; Shahzad, F.; Hong, S. M.; Kim, Y. H.; Chong, M. K. Ultrahigh Electrically and Thermally Conductive Self-Aligned Graphene/Polymer Composites Using Large-Area Reduced Graphene Oxides. Carbon 2016, 101, 120-128. (33) Kim, H. S.; Bae, H. S.; Yu, J.; Kim, S. Y. Thermal Conductivity of Polymer Composites with the Ggeometrical Characteristics of Graphene Nanoplatelets. Sci. Rep. 2016, 6, 26825-26833. (34) Yang, W.; Zhao, Z.; Wu, K.; Huang, R.; Liu, T.; Jiang, H.; Chen, F.; Fu, Q. Ultrathin Flexible Reduced Graphene Oxide /Cellulose Nanofiber Composite Films with Strongly Anisotropic Thermal Conductivity and Efficient Electromagnetic Interference Shielding. J. Mater. Chem. C 2017, 5, 3748-3756. (35) Wu, K.; Fang, J.; Ma, J.; Huang, R.; Chai, S.; Chen, F.; Fu, Q. Achieving a Collapsible, Strong and Highly Thermally Conductive Film Based on Oriented Functionalized Boron Nitride Nanosheets and Cellulose Nanofiber. ACS Appl. Mater. Interfaces 2017, 9, 30035-30045. (36) Wang, J.; Li, Q.; Liu, D.; Chen, C.; Chen, Z.; Hao, J.; Li, Y.; Zhang, J.; Naebe, M.; Lei, W. High Temperature Thermally Conductive Nanocomposite Textile by "Green" Electrospinning. Nanoscale 2018, 10, 16868-16872. (37) Malekpour, H.; Chang, K. H.; Chen, J. C.; Lu, C. Y.; Nika, D. L.; Novoselov, K. S.; Balandin, A. A. Thermal Conductivity of Graphene Laminate. Nano Lett. 2014, 14, 5155-5161. (38) Zhou, L.; Yang, Z.; Luo, W.; Han, X.; Jang, S.-H.; Dai, J.; Yang, B.; Hu, L. Thermally Conductive, Electrical Insulating, Optically Transparent Bi-Layer Nanopaper. ACS Appl. Mater. Interfaces 2016, 8, 28838-28843. (39) 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, 6197-6204. (40) Leng, J.; Lan, X.; Liu, Y.; Du, S. Shape-Memory Polymers and Their Composites: Stimulus Methods and Applications. Prog. Mater. Sci. 2011, 56, 1077-1135. (41) Behl, M.; Kratz, K.; Zotzmann, J.; Nã¶Chel, U.; Lendlein, A. Reversible Bidirectional Shape-Memory Polymers. Adv. Mater. 2013, 25, 4466-4469. (42) Xie, T.; Xiao, X. Self-Peeling Reversible Dry Adhesive System. Chem. Mater. 2008, 20, 2866-2868. (43) Xu, H.; Yu, C.; Wang, S.; Malyarchuk, V.; Xie, T.; Rogers, J. A. Deformable, Programmable, and Shape-Memorizing Micro-Optics. Adv. Funct. Mater. 2013, 23, 3299-3306. (44) Hardy, J. G.; Palma, M.; Wind, S. J.; Biggs, M. J. Responsive Biomaterials: Advances in Materials Based on Shape-Memory Polymers. Adv. Mater. 2016, 28, 5717-5724. (45) Liu, R.; Kuang, X.; Deng, J.; Wang, Y.-C.; Wang, A. C.; Ding, W.; Lai, Y.-C.; Chen, J.; Wang, P.; Lin, Z.; Qi, H. J.; Sun, B.; Wang, Z. L. Shape Memory Polymers for Body Motion Energy Harvesting and Self-Powered Mechanosensing. Adv. Mater. 2018, 30, 1705195-1705202. (46) Zhang, J.; Cao, Y.; Feng, J.; Wu, P. Graphene-Oxide-Sheet-Induced Gelation of Cellulose and Promoted Mechanical Properties of Composite Aerogels. J. Phys. Chem. C 2012, 116, 8063–8068. (47) Yang, J.; Zhang, E.; Li, X.; Zhang, Y.; Qu, J.; Yu, Z. Z. Cellulose/Graphene Aerogel Supported Phase Change Composites with High Thermal Conductivity and Good Shape Stability for Thermal Energy Storage. Carbon 2016, 98, 50-57. (48) Liang, S.; Wu, J.; Tian, H.; Zhang, L.; Xu, J. High‐Strength Cellulose/Poly(ethylene glycol) Gels. ChemSusChem 2010, 1, 558-563. (49) Li, C.; Qiu, L.; Zhang, B.; Li, D.; Liu, C. Y. Robust Vacuum-/Air-Dried Graphene Aerogels and

18


Page 18 of 20

Page 19 of 20 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


Fast Recoverable Shape-Memory Hybrid Foams. Adv. Mater. 2016, 28, 1510-1516.

19



270x166mm (150 x 150 DPI)


Page 20 of 20

Flexible Films for Smart Thermal Management: Influence of Structure

Recommend Documents