Melamine Foam Supported Form-stable Phase Change Materials with

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Energy, Environmental, and Catalysis Applications

Melamine Foam Supported Form-stable Phase Change Materials with Simultaneous Thermal Energy Storage and Shape Memory Property for Thermal Management of Electronic Devices Jun-hao Jing, Hai-yan Wu, Yao-wen Shao, Xiao-dong Qi, Jing-hui Yang, and Yong Wang ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.9b06198 • Publication Date (Web): 09 May 2019 Downloaded from http://pubs.acs.org on May 9, 2019

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ACS Applied Materials & Interfaces

Melamine Foam Supported Form-stable Phase Change Materials with Simultaneous Thermal Energy Storage and Shape Memory Property for Thermal Management of Electronic Devices Jun-hao Jing, Hai-yan Wu, Yao-wen Shao, Xiao-dong Qi*, Jing-hui Yang, Yong Wang* School of Materials Science and Engineering, Southwest Jiaotong University, Key Laboratory of Advanced Technologies of Materials, Ministry of Education of China, Chengdu 610031, P. R. China

Abstract: Paraffin wax (PW) is widely used as phase change materials (PCMs) in the thermal energy storage field, whereas the leakage and strong rigidity of PW have hindered its practical applications. In this work, binary melamine foam (MF)/PW blends with simultaneous thermal energy storage and shape memory properties were prepared through vacuum impregnation. Herein, PW performs as a latent heat storage material and a switching phase for shape fixation, and MF serves as a supporting material to prevent the leakage and a permanent phase for shape recovery. Due to the light weight and super elasticity of MF, the MF/PW PCMs not only possess good encapsulation ability and high latent heat, but also possess excellent shape fixing and recovery properties (shape fixing and recovery ratios are about 100 %). Besides, the MF/PW PCMs can be fabricated into arbitrary shapes using MF as a template, and the MF/PW PCMs exhibit excellent shape memory cyclic performance and thermal

*

Corresponding author: E-mail: [email protected] (Xiao-dong Qi); [email protected](Yong Wang)

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reliability. A temperature-sensitive and temperature-controlled deployable panel is further established, which can be installed in the electronic device and used for the temperature protection. With high thermal energy storage capability, excellent shape memory properties, shape designability and stable cycling reliability, this multi-functional MF/PW PCM show a promising application in the thermal energy management systems. Keyword: phase change; shape memory property; paraffin; melamine foam; deployable panel

1. Introduction With the increase of energy consumption, intensive efforts have been done on the effective energy storage and conversion.1-3 Energy storage technology has attracted great attention due to its capability of reducing the mismatch between energy demand and supply.4 Because of good energy storage properties and small temperature change from energy storage to retrieval, latent heat storage systems are widely applied to improve the energy utilization efficiency and solve the energy imbalance.5,6 As a kind of advanced energy saving materials, phase change materials (PCMs) can absorb and store thermal energy by making full use of large quantities of latent heat during phase change process.7 Among various organic and inorganic PCMs, paraffin wax (PW) is commonly used due to its low cost, non-toxicity, adaptable phase change temperature and thermal stability.8 However, PW suffers from the liquid


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leakage during phase change process, resulting in the decrease of thermal energy storage efficiency and environment pollution.9 Several methods including microencapsulation, physical absorption, coaxial electrospinning are proposed to solve the leakage issue.10-14 Even if the leakage of PW can be improved by selecting appropriate supporting materials, the installation between form-stable PCMs and controlled device is still one growing problem that needs to be considered.15,16 The strong rigidity of PCMs may induce easy brittle fracture and poor installation in micro-electronic devices.17 Hence, it is necessary to fabricate a novel kind of PCMs which can possess shape variation ability in installation process and meanwhile have high latent heat.18,19 Shape memory polymers (SMPs) as a type of intelligent materials, have the ability to fix the deformed shape and recover to original shape upon exposure to external stimuli.20-22 Conventional SMPs contain two structural components: the reversible switching phase and the permanent phase.23 The reversible phase determines the shape memory transition and the permanent phase is responsible for memorizing the initial shape. Inspired by the two-phase structure of SMPs, if the supporting material possess good elasticity, the composite PCMs by blending PCMs with elastic materials are expected to exhibit shape memory properties.24-27 For example, Feng et al and Weiss et al blended elastomers with crystalline small-molecules (such as PW, fatty acid, etc.), the blends exhibited good shape fixing and recovery properties.25,28 Therefore, the phase change energy storage property and shape memory property are two attractive properties that can endow the materials



with thermal energy storage and shape variation capabilities at the same time, which will greatly widen the applications of PCMs. With this in mind, the selection of supporting material is important for the macroscopic physical properties of PCMs. Melamine foam (MF), as a three-dimensional (3D) porous material, has been widely used as the main building block to develop novel 3D porous composite materials.29 MF has an interconnected network and a high open porosity of 99% with pore size of about 100 μm. Moreover, MF possesses excellent elasticity, this means MF can be deformed and quickly recover to its original shape without structural fatigue.30-32 Considering the porous structure and super elasticity of MF, the unique binary structure of MF/PW blends may combine the advantages of both PW and MF, which imparts MF/PW blends not only with high latent heat but also with excellent shape memory property, thus holding great application prospect in the thermal management of microelectronic devices. In this work, we employ MF as a highly porous and flexible scaffold to prepare form-stable PCMs with simultaneous high latent heat and shape memory properties. On one hand, the low-density MF provides a 3D connected framework to completely encapsulate PW without compromising the latent heat. On the other hand, the elastic MF imparts the MF/PW PCMs with shape variation ability by triggering the phase transition of PW. The MF/PW PCMs can realize many deformation behaviors such as bend and compression, which are helpful for the installation. Therefore, combination of multiple functions including form stability, high thermal energy storage ability, good shape fixing and recovery property, shape designability and thermal reliability is


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realized in MF/PW PCMs, which sets our work apart from previously reported PCMs. The materials used for fabricating the flexible PCMs are all industrial products with low cost, and therefore this kind of flexible PCMs is expected to realize large-scale preparation.

2. Materials and methods 2.1 Materials Paraffin wax (PW) with a melting temperature of 52 oC was purchased from Sinopharm Chemical Reagent Co., Ltd. Commercially available melamine foam (MF) was supplied by Xiamen Share Nano Technology Co., Ltd. The detailed textural properties of MF are shown in Figure S1. 2.2 Sample preparation The preparation process of MF/PW PCMs is shown in Figure 1a. Firstly, 3 g of PW was dissolved in the cyclohexane solution (47 mL) at 60 oC for 1 h. Then, MF (3 cm × 2 cm × 1 cm) was immersed into the PW/cyclohexane solution to absorb PW under the vacuum condition. After certain minutes (1 ~ 60 min), the resulting material was placed on a glass plate at 50 oC to remove the cyclohexane and finally the MF/PW PCMs were obtained. To evaluate the absorbability of MF, different concentrations of PW/cyclohexane solution and immersion times were conducted. 2.3 Characterizations The morphology of MF/PW PCMs was observed on a scanning electron microscope (SEM) Fei Inspect (FEI, Netherlands). The structure of MF/PW PCMs



was investigated by the Fourier transform infrared spectroscope (FTIR, Thermo Nicolet, USA) and X-ray diffraction (XRD, Panalytical Empyrean, Netherlands). The FTIR spectrum was recorded with an attenuated total reflection (ATR) mode and the wavenumber range was set at 400-4000 cm−1. The XRD scanning angle was ranged from 5° to 50°. The thermal properties of MF/PW PCMs were studied on a differential scanning calorimeter (DSC) STA 449C (Netzsch, Germany). The samples (about 6 mg) were firstly heated to 100 oC at 10 oC/min and then they were cooled down to 0 oC at 10 oC/min. Shape stability measurements were carried out on a rheometer (TA DHR-1, USA). The temperature was heated from 20 oC to 100 oC at 5 oC/min

and the constant force was kept at 0.25 N. The thermal energy storage/release

behavior of MF/PW PCMs was characterized by an infrared thermal imaging camera (FLIR T620, USA). The sample was placed on a heating apparatus (80 oC) for 10 min and then removed to allow the sample to cool naturally. The thermal-actuated shape memory properties of MF/PW PCMs were evaluated through a bend-recovery test. A four-step procedure was designed as follows: (1) the sample was firstly heated to 60 °C and then bent in half (180 °); (2) the deformed sample was cooled to 20 °C under an external force; (3) the external force was unloaded and the temporary angle (𝜃1) was recorded; (4) the sample was reheated to 60 °C and the final recovery angle (𝜃2) was recorded. The whole shape fixing and recovery behaviors were recorded by a digital camera. The shape recovery ratio (𝑅𝑟) and shape fixing ratio (𝑅𝑓) of MF/PW PCMs were quantitatively calculated according to the following equations (1) and (2).


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𝑅𝑟 =

θ1 ― θ2 𝜃1

× 100%

θ1

𝑅𝑓 = 180 × 100%

(1) (2)

3. Results and discussion 3.1 Characterization of MF/PW PCMs MF/PW PCMs with different composition ratios were prepared through vacuum impregnation. In order to measure the absorbing capacity of porous MF, the effects of immersion time and solution concentration were studied. Figure 1b, c shows the weight ratio of PW/MF under different immersion times and solution concentrations. At a constant solution concentration (0.25 g/mL), the weight ratio of PW/MF does not change obviously as the immersion time rangs from 1 min to 60 min, indicating that the absorbability of MF is independent of immersion time. When fixing the immersion time (1 min), the weight ratio of PW/MF increases linearly with the solution concentration. The weight ratio of PW/MF increases from 5 to 30 when the solution concrentration ranges from 0.05 to 0.40 g/mL. Here, the binary MF/PW PCMs are denoted as MF-PWx, where x represents the wight ratio of absorbed PW to MF. The morphology of MF/PW PCMs was investigated by SEM. MF exhibits a 3D continuous network and the surface of the skeleton is smooth. With the open macropores (about 100 μm), MF has the large capillary force and surface tension to absorb PW into the inner pores.33 For MF-PW10, the absorbed PW is presented in the pores or along the skeleton of MF (Figure 1d). After mixing with 20 times of PW, the PW in the pores of MF becomes more impact (Figure 1e). Therefore, MF is



successfully utilized as 3D porous matrix to encapsulate PW through simple vacuum impregnation. To further confirm the structure of MF/PW PCMs, FTIR and XRD analysis were conducted. No significant change of peak is observed in the FTIR and XRD patterns, indicating that MF and PW are physical combination (Figure S2).

Figure 1. (a) Schematic diagram illustrating the preparation process of MF/PW PCMs. (b, c) Weight ratio variation of PW/MF as a function of immersion time and solution concentration. (d, e) SEM images of MF-PW10 and MF-PW20.

3.2 Melting-freezing behavior of MF/PW PCMs


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Phase change enthalpy is an important parameter to evaluate the thermal energy storage efficiency of PCMs. Figure 2 displays the DSC melting-freezing curves of MF/PW PCMs in the first phase change cycle, and the corresponding thermal parameters are summarized in Table 1. Pure PW presents two melting peaks, the first one at about 35 oC is assigned to the solid-solid phase transition (crystal-rotator transition), and the second one at about 55.9 oC is assigned to the solid-liquid phase transition (rotator-liquid transition).34,35 Similar phenomenon is also seen in the cooling thermograms (Figure 2b). Here, the second melting and crystallization peaks are defined as the melting temperature (𝑇𝑚) and crystallization temperature (𝑇𝑐) of PW, respectively. The melting-freezing characteristics of MF/PW PCMs are similar to those of pure PW, because there is no chemical reaction between PW and MF. As one of the most important phase change performances, the enthalpy of MF/PW PCMs strongly depends on the encapsulation ratio of PW. With the increase of PW content, the melting enthalpy (∆𝐻𝑚) of MF/PW PCMs increases from 124.2 to 139.8 J/g. Since only PW provides the latent heat in MF/PW PCMs, it is not surprising that the ∆𝐻𝑚 of MF/PW PCMs increases monotonically with the increased PW content. The thermal storage efficiency of PW in the MF/PW PCMs is calculated from 78.4% to 88.3% compared with pure PW, which is relatively lower than the corresponding PW content (90.9% to 96.8%). It might be that not all PW can provide the endothermic and exothermic enthalpy, because the melting and crystallizing behavior of PW would be spatially restricted in the confined macropores of MF. Nevertheless, the MF/PW PCMs still have relatively higher thermal storage capability than other form-stable



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PCMs encapsulated by polymers.34-37 This is ascribed to the low density and abundant porosity of MF, PW can be absorbed into MF with an extremely high loading of approximately 3000 wt%, which is about two orders of magnitude higher than those mostly reported form-stable PCMs encapsulated by polymers.34-37

Figure 2. (a) DSC heating curves and (b) cooling curves of PW and MF/PW PCMs. Table 1. Thermal characteristics of PW and MF/PW PCMs. Sample

PW content (wt%)

𝑇𝑚/℃

𝑇𝑐/(℃)

∆𝐻𝑚/(J g-1)

∆𝐻𝑐/(J g-1)

PW

100

57.5

46.3

158.4

155.6

MF-PW10

90.9

56.0

45.9

124.2

121.6

MF-PW15

93.8

55.6

44.3

130.4

126.5

MF-PW20

95.2

56.3

45.3

134.5

130.8

MF-PW25

96.2

56.6

45.6

137.4

132.6

MF-PW30

96.8

56.8

45.1

139.8

134.2

3.3 Shape stability of MF/PW PCMs


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Encapsulation property is also one of the important parameters to determine the service life of PCMs. The shape stabilities of MF/PW PCMs were comparatively investigated and the results are shown in Figure 3. Upon heating above 55 oC, pure PW melts and its dimension decreases seriously. In contrast, the dimension of MF/PW PCMs changes little even at 80 oC, which is ascribed to the effective support of the 3D framework in MF. The shape stability of MF/PW PCMs is further visually illustrated by their digital photographs (Figure 3b). Solid PW holds the shape at 30 oC, but completely liquidizes when heated to 80 oC. Because of the existence of MF, all the MF/PW PCMs keep their stable shape at 80 oC. Even compressed by a weight of 20 g, MF/PW PCMs still maintain their original shape and have no obvious leakage of PW. This phenomenon indicates that MF is an ideal supporting material to completely encapsulate PW and thus prevents the leakage of melted PW.

Figure 3. (a) Thermomechanical analyses of PW and MF/PW PCMs. (b) Right photograph showing the shape stability of PW and MF/PW PCMs at 30 oC and 80 oC.



3.4 Thermal energy storage/release behavior of MF/PW PCMs Since MF/PW PCMs have high latent heat and good shape stability, the thermal energy storage/release behavior of MF-PW20 PCM was then investigated. The sample was placed on a heating apparatus (80 oC) for 10 min and then quickly removed to allow the sample to cool. The infrared thermal imager was applied to directly observe the heating and cooling processes. As shown in Figure 4a, during the heating process, the temperature of sample gradually increases from 15 oC to 47 oC in 4 min and keeps constant at 47 oC for 4 min. This melting plateau is corresponded to the solid-liquid phase transition of PW. MF-PW20 absorbs heat during phase change and maintains the temperature around the 𝑇𝑚 of PW. After removing the heating apparatus, the temperature achieves a plateau at about 45 oC and the stabilization time is as long as 6 min, suggesting that the thermal energy stored during the melting process is released. When the stored energy is completely released, the temperature of sample gradually recovers to the ambient temperature under the natural cooling. Figure 4b presents the temperature-time curves during the melting and cooling process. It is noteworthy that two temperature plateaus are observed, which are corresponded to the melting transition and the crystalline transition of PW, respectively. There exists a small temperature change from thermal energy storage to retrieval. Therefore, the MF/PW PCMs exhibit excellent thermal management capacity because the plateau time can be maintained for a long time. The charging/discharging characteristics of PCMs are mainly dependent on their thermal conductivity. MF is an insulation material with low thermal conductivity, and the


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thermal conductivity of the obtained MF/PW PCMs is about 0.3 W m-1 K-1, which is lower than other thermally conductive PCMs. It’s known that MF can work as an ideal

supporting

substrate

to

support

3D

interconnected

network

of

thermal-conductive nanofillers including carbon nanotubes (CNTs), graphene, boron nitride (BN), etc.29 The MF-templated nanofiller framework will help to increase the thermal conductivity of PCMs and accelerate the thermal charging/discharging rates. This will be investigated in our following work.



Figure 4. (a) Infrared images showing the thermal energy storage/release behavior of MF-PW20. The heating apparatus was maintained at 80 ℃ for 10 min and then removed. (b)Time-dependent temperature evolution curves of MF-PW20.

3.5 Shape memory property of MF/PW PCMs In addition to the latent heat and encapsulate effect, the strong rigidity of PCMs gives rise to easy brittle failure and high installation difficulty, which greatly restricts the practical applications.15 Hence, flexible PCMs with shape variation ability are urgently required. It’s known that MF possesses an excellent elasticity, but it cannot fix the deformed shape at room temperature (25 ℃). From above analysis, PW is fulfilled in the macropores of MF. The combination of rigid PW and elastic MF may impart MF/PW PCMs with huge feasibility of shape variation.38 To confirm this assumption, the thermal-actuated shape memory effects of MF/PW PCMs were then investigated. Figure 5a displays the visual shape fixing and shape recovery behaviors of MF/PW PCMs. On one hand, all the samples can be eaisly deformed into “U” shape at 60 ℃ and well fix the temporary shape at 25 ℃, suggesting that MF/PW PCMs possess the good shape fixing property. On the other hand, the temporary shape (“U” shape) quickly recovers to the original straight shape when samples are reheated to 60 ℃. Therefore, the thermal-actuated shape deformation and recovery above the 𝑇𝑚 of PW and shape fixation below that point are successfully achieved. Figure 5b quantitatively presents the variation of shape recovery ratio of MF/PW PCMs as a function of time. The shape recovery time


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increases when the MF/PW ratio ranges from 1:10 to 1:30. This is attributed to the elastic MF provides the shape recovery forces. The more MF content, the faster shape recovery effect is. In addition to the bended shape, the MF/PW PCMs can also been compressed and fully recovered to their original shape under heating (Figure S3). Figure 5c illustrates the thermal-actuated shape memory mechanism. For MF/PW PCMs, the crystallization and melting of PW crystals play the role of fixing or unfixing temporary shape, and the resilience force of MF is responsible for recovering to original shape. Upon heating above the 𝑇𝑚 of PW, the PW crystals melt (Step 1), and the MF/PW PCMs become flexible and can be easily deformed to a temporary shape (Step 2). Through rapidly cooling to room temperature (25 ℃), PW crystallizes in the macropores of MF (Step 3). Since the 𝑇𝑐 of PW is higher than 25 ℃, the strength of MF/PW PCMs originated from PW crystals is higher than the resilience force of MF. The temporary shape can be well fixed after releasing the external load, resulting from the rigid PW crystals. When the temperature is reheated to the 𝑇𝑚 of PW, PW crystals melt again. The stored resilience of MF is released without the prevention of PW crystals and drives the MF/PW PCMs recover to their original shapes (Step 4). In this work, the di-functional MF/PW blends which possess phase change property and shape memory property are obtained. The shape recovery speed is strongly related to the resilience force of MF. However, the thermal energy storage capability reduces with the increase of MF content, because only PW provides the phase change enthalpy (see Figure 2). Therefore, the MF-PW20 PCM (the weight



ratio of MF to PW is 1:20) is considered to have a balanced thermal energy storage property and shape recovery property.

Figure 5. (a) Digital photos showing that MF/PW PCMs recover from a temporary bended shape to an original straight shape. (b) Shape recovery ratio of MF/PW PCMs as a function of time. (c) Shape memory mechanism of MF/PW PCMs.


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Due to the interconnected framework of MF, MF is often used as a template to design novel 3D porous materials.30 From the SEM observation, PW is fulfilled in the pores or along the skeleton of MF. Take MF-PW20 as an example, the MF-PW20 PCM can be fabricated into arbitrary shapes using the MF templates with exactly the same shapes, such as square, triangle, trapezoid, pentagonal star, heart, etc (Figure 6). Moreover, these MF-PW20 PCMs with arbitrary shapes can be easily deformed above the 𝑇𝑚 of PW, fix the temporary shape at room temperature (25 ℃) and finally recover their original shape upon reheating to 60 ℃. Besides, no leakage of melted PW is found during the whole thermal-actuated shape memory process, which confirms the improved encapsulation property of MF/PW PCMs. Therefore, the form-stable MF/PW PCMs are capable to exhibit outstanding shape fixation and recovery performances, which show the potential application in the thermal management of devices with limited space.

Figure 6. Arbitrary-shaped MF-PW20 PCMs using MF as a building template. These



MF-PW20 PCMs with arbitrary shapes show good shape fixing and recovery effect.

3.6 Shape memory reliability and thermal stability of MF/PW PCMs Reliability and stability are two important issues for PCMs in view of the long-term usage. The MF-PW20 PCM has balanced latent heat and shape memory property. Therefore, take the MF-PW20 PCM as an example, the cyclic thermal-actuated shape behavior and the thermal stability were evaluated. Figure 7a displays the thermal-actuated shape recovery behaviors of MF-PW20 PCM after 1, 3 and 5 cycles. No obvious change is observed in terms of shape recovery effect and speed after 5 cycles, indicating that MF-PW20 PCM has a quite stable shape memory property. Meanwhile, DSC measurement was conducted to investigate the thermal stability of MF-PW20 PCM. As shown in Figure 7b, the phase change temperatures and enthalpies almost change negligibly after 100 cycles. These results reveal that MF-PW20 PCM exhibits excellent cyclic shape memory property and thermal stability, which is helpful for the long-term usability in practical applications.


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Figure 7. (a) Thermal-actuated shape recovery behaviors of MF-PW20 PCM after 1, 3 and 5 cycles. (b) DSC heating and cooling curves of the MF-PW20 PCM with cycling of 100 times.

3.7 Thermal management of electronic devices With the miniaturization and integration of electronic devices, timely dissipation of excess heat during their high-speed running becomes a challenge, which severely limits the lifetime of electronic devices.39 PCMs have large latent heat with regarding to melting and solidifying at a nearly constant temperature, which are expected to solve the problem of excess heat dissipation. Based on the above results, the MF/PW PCMs possess the simultaneous abilities of thermal energy storage and shape variation. The materials can show some advantages in the thermal management of electronic devices. As shown in Figure 8, the MF-PW20 PCM is used as a deployable panel and guarantees the temperature constancy of electronic devices. On one hand, the shape fixation and recovery properties impart the MF/PW PCMs with good installation ability. The MF-PW20 sample is heated and compressed to a smaller shape, and then can be conveniently installed on a mainboard of electronic devices. Figure 8a, b presents that the compressed sample recovers to the initial square shape when the temperature of mainboard is too high (above the 𝑇𝑚 of PW). The fully expanded sample can cover the mainboard of electronic devices. On the other hand, the large latent heat endows the MF/PW PCMs with excellent thermal energy storage ability. One can observe that the surface temperature of sample keeps constant at the



𝑇𝑚 of PW, suggesting a small temperature variation (Figure 8c). This is ascribed to the solid-to-liquid transition of PW and the thermal energy is stored in the form of latent heat. The development of PCMs with shape memory property becomes important as they can be easily installed and reduce the occupied room in the confined electronic devices. The flexible MF/PW PCMs can be used to produce deployable panels which can be compressed and packed in the electronic devices, deploy into the expanded shape if the temperature gets too high, and ultimately keep the internal temperature constant and thus avoid overheating of electronic devices.

Figure 8. (a) Digital photographs show the MF-PW20 PCM can work as a deployable panel on the mainboard of electronic devices. (b) Infrared photographs show the


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shape recovery from a compressed shape to a square shape when the temperature of mainboard is above the 𝑇𝑚 of PW. (c) The MF-PW20 PCM stores excess heat and keeps the internal temperature constant.

4. Conclusions In this work, a novel kind of multi-functional materials which possesses large latent heat, good encapsulation ability and shape memory property is prepared. The materials are composed of PW (a cystallizable material works as a latent heat storage material and a switching phase for shape transition), and MF (an elastic foam serves as a supporting material and a permanent phase for shape recovery). The morphology, phase change performance, thermal energy storage and thermal-actuated shape memory behaviors of MF/PW PCMs are systematically investigated. The results indicate that the MF/PW PCMs exhibit no liquid leakage, high latent heat, and excellent thermal-actuated shape fixing and recovery properties (shape fixing and recovery ratios are about 100 %). Because the MF/PW PCMs are both temperature-sensitive and temperature-controlled, a deployable panel used for the temperature protection of electronic devices is further exploited. Considering the facile preparation, low cost, high thermal energy storage ability and shape memory property, the MF/PW PCMs may exhibit great application prospects in the thermal management of micro-electronic devices.

Supporting Information Available



SEM image of MF; Raman spectrum of MF; FTIR spectrum of MF; Corresponding element mapping image of MF; FTIR spectra of PW and MF/PW PCMs; XRD patterns of PW and MF/PW PCMs; Digital photographs showing that MF/PW PCMs recover from a temporary compressed shape to an original shape.

AUTHOR INFORMATION Corresponding Author E-mail: [email protected] (Xiao-dong Qi); [email protected] (Yong Wang).

Notes The authors declare no competing financial interest.

Acknowledgments We would like to express our sincere thanks to the National Natural Science Foundation of China (Grant No. 51473137, 51803172), the Key Research and Development Program of Sichuan Province (Grant No. 2017GZ0406 and 2019YFG0241) and the Fundamental Research Funds for the Central Universities of China (Grant No. A0920502051820-45).

References (1) Sharma, A.; Tyagi, V. V.; Chen, C. R.; Buddhi, D. Review on Thermal Energy Storage with Phase Change Materials and Applications. Renewable and Sustainable Energy Rev. 2009, 13, 318-345. (2) Kenisarin, M. M.; Kenisarina, K. M. Form-stable Phase Change Materials for Thermal Energy Storage. Renewable and Sustainable Energy Rev. 2012, 16, 1999-2040.


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(3) Qu, Z.; Shi, M.; Wu, H.; Liu, Y.; Jiang, J.; Yan, C. An Efficient Binder-free Electrode with Multiple Carbonized Channels Wrapped by NiCo2O4 Nanosheets for High-performance Capacitive Energy Storage. J. Power Sources 2019, 410-411, 179-187. (4) Zalba, B.; Marin, J. M.; Cabeza, L. F.; Mehling, H. Review on Thermal Energy Storage with Phase Change: Materials, Heat Transfer Analysis and Applications. Appl. Therm. Eng. 2003, 23, 251-283. (5) Huang, X.; Alva, G.; Jia, Y.; Fang, G. Morphological Characterization and Applications of Phase Change Materials in Thermal Energy Storage: A Review. Renewable and Sustainable Energy Rev. 2017, 72, 128-145. (6) Huang, X. B.; Chen, X.; Li, A.; Atinafu, D.; Gao, H. Y.; Dong, W. J.; Wang, G. Shape-stabilized Phase Change Materials Based on Porous Supports for Thermal Energy Storage Applications. Chem. Eng. J. 2019, 356, 641-661. (7) Wei, X.; Xue, F.; Qi, X. D.; Yang, J. H.; Zhou, Z. W.; Yuan, Y. P.; Wang, Y. Photo- and Electro-responsive Phase Change Materials Based on Highly Anisotropic Microcrystalline Cellulose/Graphene Nanoplatelet Structure. Appl. Energy 2019, 236, 70-80. (8) Chen, L.; Zou, R.; Xia, W.; Liu, Z.; Shang, Y.; Zhu, J.; Wang, Y.; Lin, J.; Xia, D.; Cao, A. Electro- and Photodriven Phase Change Composites Based on Wax-infiltrated Carbon Nanotube Sponges. ACS Nano 2012, 6, 10884-10892. (9) Lian, Q.; Li, Y.; Sayyed, A. A. S.; Cheng, J.; Zhang, J. Facile Strategy in Designing Epoxy/Paraffin Multiple Phase Change Materials for Thermal Energy Storage Applications. ACS Sustain. Chem. Eng. 2018, 6, 3375-3384. (10) Gao, H. Y.; Wang, J. J.; Chen, X.; Wang, G.; Huang, X. B.; Li, A.; Dong, W. J. Nanoconfinement Effects on Thermal Properties of Nanoporous Shape-stabilized Composite PCMs: A Review. Nano Energy 2018, 53, 769-797. (11) Lu, Y.; Xiao, X.; Zhan, Y.; Huan, C.; Qi, S.; Cheng, H.; Xu, G. Core-Sheath Paraffin-Wax-Loaded Nanofibers by Electrospinning for Heat Storage. ACS. Appl. Mater. Interfaces 2018, 10, 12759-12767. (12) Wang, J.; Yang, M.; Lu, Y.; Jin, Z.; Tan, L.; Gao, H.; Fan, S.; Dong, W.; Wang, G. Surface Functionalization Engineering Driven Crystallization Behavior of Polyethylene Glycol Confined in Mesoporous Silica for Shape-stabilized Phase Change Materials. Nano Energy 2016, 19, 78-87. (13) Tang, J.; Fan, S.; Dong, W.; Wang, J.; Gao, H.; Yang, M.; Yang, M.; Wang, G.



Imine-linked Micron-network Polymers with High Polyethylene Glycol Uptake for Shaped-stabilized Phase Change Materials. RSC Adv. 2016, 6, 44807-44813. (14) Atinafu, D. G.; Dong, W.; Wang, C.; Wang, G. Synthesis of Porous Carbon From Cotton Using an Mg(OH)2 Template for Form-stabilized Phase Change Materials with High Encapsulation Capacity, Transition Enthalpy and Reliability. J. Mater. Chem. A 2018, 6, 8969-8977. (15) Li, W. W.; Cheng, W. L.; Xie, B.; Liu, N.; Zhang, L. S. Thermal Sensitive Flexible Phase Change Materials with High Thermal Conductivity for Thermal Energy Storage. Energy Convers. Manage. 2017, 149, 1-12. (16) Sun, Q. R.; Zhang, H. Q.; Xue, J. J.; Yu, X. P.; Yuan, Y. P.; Cao, X. L. Flexible Phase Change Materials for Thermal Storage and Temperature Control. Chem. Eng. J. 2018, 353, 920-929. (17) Aftab, W.; Mahmood, A.; Guo, W.; Yousaf, M.; Tabassum, H.; Huang, X.; Liang, Z.; Cao, A.; Zou, R. Polyurethane-based Flexible and Conductive Phase Change Composites for Energy Conversion and Storage. Energy Storage Mater. 2018, DOI:10.1016/j.ensm.2018.10.014. (18) Zhang, Q.; He, Z.; Fang, X.; Zhang, X.; Zhang, Z. Experimental and Numerical Investigations on a Flexible Paraffin/Fiber Composite Phase Change Material for Thermal Therapy Mask. Energy Storage Mater. 2017, 6, 36-45. (19) Wu, W.; Wu, W.; Wang, S. Form-stable and Thermally Induced Flexible Composite Phase Change Material for Thermal Energy Storage and Thermal Management Applications. Appl. Energy 2019, 236, 10-21. (20) Lendlein, A.; Kelch, S. Shape-Memory Polymers. Angew. Chem., Int. Ed. 2002, 41, 2034-2057. (21) Hu, J.; Zhu, Y.; Huang, H.; Lu, J. Recent Advances in Shape-memory Polymers: Structure, Mechanism, Functionality, Modeling and Applications. Prog. Poly. Sci. 2012, 37, 1720-1763. (22) Zhao, Q.; Qi, H. J.; Xie, T. Recent Progress in Shape Memory Polymer: New Behavior, Enabling Materials, and Mechanistic Understanding. Prog. Poly. Sci. 2015, 49-50, 79-120. (23) Liu, C.; Qin, H.; Mather, P. T. Review of Progress in Shape-memory Polymers. J. Mater. Chem. 2007, 17, 1543-1558. (24) Du, J.; Liu, D.; Zhang, Z.; Yao, X.; Wan, D.; Pu, H.; Lu, Z. Dual-responsive Triple-shape Memory Polyolefin Elastomer/Stearic Acid Composite. Polymer 2017,


Page 24 of 27

Page 25 of 27 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


126, 206-210. (25) Song, S.; Feng, J.; Wu, P. A New Strategy to Prepare Polymer-based Shape Memory Elastomers. Macromol. Rapid Commun. 2011, 32, 1569-1575. (26) Li, G.; Zhang, H.; Fortin, D.; Fan, W.; Xia, H.; Zhao, Y. A Composite Material with Room Temperature Shape Processability and Optical Repair. J. Mater. Chem. C 2016, 4, 5932-5939. (27) Du, J.; Zhang, Z.; Liu, D.; Ren, T.; Wan, D.; Pu, H. Triple-stimuli Responsive Shape Memory Effect of Novel Polyolefin Elastomer/Lauric Acid/Carbon Black Nanocomposites. Compos. Sci. Technol. 2019, 169, 45-51. (28) Brostowitz, N. R.; Weiss, R. A.; Cavicchi, K. A. Facile Fabrication of a Shape Memory Polymer by Swelling Cross-Linked Natural Rubber with Stearic Acid. ACS Macro Lett. 2014, 3, 374-377. (29) Feng, Y.; Yao, J. Design of Melamine Sponge-Based Three-Dimensional Porous Materials toward Applications. Ind. Eng. Chem. Res. 2018, 57, 7322-7330. (30) Li, C. W.; Jiang, D. G.; Liang, H.; Huo, B. B.; Liu, C. Y.; Yang, W. R.; Liu, J. Q. Superelastic and Arbitrary-Shaped Graphene Aerogels with Sacrificial Skeleton of Melamine Foam for Varied Applications. Adv. Funct. Mater. 2018, 28, 1704674. (31) Wu, C.; Huang, X.; Wu, X.; Qian, R.; Jiang, P. Mechanically Flexible and Multifunctional Polymer-based Graphene Foams for Elastic conductors and Oil-water Separators. Adv. Mater. 2013, 25, 5658-5662. (32) Ge, J.; Yao, H. B.; Wang, X.; Ye, Y. D.; Wang, J. L.; Wu, Z. Y.; Liu, J. W.; Fan, F. J.; Gao, H. L.; Zhang, C. L; Yu, S. H. Stretchable Conductors Based on Silver Nanowires: Improved Performance Through a Binary Network Design. Angew. Chem., Int. Ed. 2013, 52, 1654-1659. (33) Qin, M.; Xu, Y.; Cao, R.; Feng, W.; Chen, L. Efficiently Controlling the 3D Thermal

Conductivity

of

a

Polymer

Nanocomposite

via

a

Hyperelastic

Double-Continuous Network of Graphene and Sponge. Adv. Funct. Mater. 2018, 28, 1805053. (34) Zhang, Q.; Zhao, Y.; Feng, J. Systematic Investigation on Shape Stability of High-efficiency SEBS/Paraffin Form-stable Phase Change Materials. Sol. Energ. Mat. Sol. Cells 2013, 118, 54-60. (35) Zhang, Q. L.; Feng, J. C. Difunctional Olefin Block Copolymer/paraffin Form-stable Phase Change Materials with Simultaneous Shape Memory Property. Sol. Energ. Mat. Sol. Cells 2013, 117, 259-266.



(36) Chen, F.; Wolcott, M. Polyethylene/Paraffin Binary Composites for Phase Change Material Energy Storage in Building: A Morphology, Thermal Properties, and Paraffin Leakage Study. Sol. Energ. Mat. Sol. Cells 2015, 137, 79-85. (37) Mu, M.; Basheer, P. A. M.; Sha, W.; Bai, Y.; McNally, T. Shape Stabilised Phase Change Materials Based on a High Melt Viscosity HDPE and Paraffin Waxes. Appl. Energy 2016, 162, 68-82. (38) Pantoja, M.; Alvarado, T.; Cakmak, M.; Cavicchi, K. A. Stearic Acid Infused Polyurethane Shape Memory Foams. Polymer 2018, 153, 131-138. (39) 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, 2019, 13, 337-345.


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Melamine Foam Supported Form-stable Phase Change Materials with

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