Fabrication of Flexible and Superhydrophobic Melamine Sponge with

Article Cite This: Ind. Eng. Chem. Res. XXXX, XXX, XXX−XXX

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Fabrication of Flexible and Superhydrophobic Melamine Sponge with Aligned Copper Nanoparticle Coating for Self-Cleaning and Dual Thermal Management Properties Hao Zhou,†,‡ Tao Zhang,*,‡ Xuejie Yue,‡ Yinxian Peng,*,† Fengxian Qiu,‡ and Dongya Yang‡ †

School of Environmental and Chemical Engineering, Jiangsu University of Science and Technology, Zhenjiang 212003, China School of Chemistry and Chemical Engineering, Jiangsu University, Zhenjiang 212013, China

Ind. Eng. Chem. Res. Downloaded from pubs.acs.org by UNIV OF ADELAIDE on 03/19/19. For personal use only.

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ABSTRACT: In this work, a three-dimensional (3D) flexible copper coated melamine sponge (Cu-MES) with superhydrophobic properties capable of active heating and infrared insulation is fabricated via deposition of copper nanoparticles on the MES surfaces for personal thermal management applications. The results showed that the Cu nanoparticles were tightly anchored on the surface of the melamine sponge, forming a low infrared emissivity coating, resulting in high thermal insulation properties of the multifunctional Cu-MES. The promising electrical conductivity grants the superior Joule heating for extra warmth of 40 °C using a low supply voltage around 7 V. Besides, obtained Cu-MES material shows a selfcleaning property with a stable water contact angle of 157.5° and a sliding angle of 15°. These promising results including low infrared emissivity for high thermal insulation and high conductivity for heat collection make the Cu-MES promising candidates for applications in personal thermal management, energy regulation, and other facilities. backs.11 Considerable amounts of energy are consumed in the maintenance of the temperature of empty space and inanimate objects inside the building rather than focusing on humans.4 Furthermore, heating systems such as air conditioners can only work in indoor spaces. Therefore, it is urgent to explore a convenient and portable heating device for applications in personal thermal management. Utilizing the resistance heating effect, the electric heating of functional materials has proven to be an economic and effective method for personal thermal management, which can adjust body temperature to a thermally safe and comfort state.12,13 Currently, intensive research efforts have focused on emerging nanomaterials for thermal management applications, including carbon nanotubes (CNTs),14 graphite nanosheets,14 and metal nanowires,15 or their mixtures as heating elements in resistive heaters. Typically, Yang et al.16 devised copper nanowires that possess the excellent heating and mechanical properties. Nevertheless, insufficient thermal management properties derived from the rapid heat transfer limits the practical application of this copper nanowires. Guo et al.17 fabricated flexible and foldable graphene paper for heating and cooling application. Although graphene materials have excellent personal thermal management properties, the complex equipment, expensive and

1. INTRODUCTION Normal body temperature plays a pivotal role in maintaining normal physiological function of humans, because for every 1 °C decrease in the body, basal metabolism is reduced by 12% and immunity is reduced by 37%.1,2 In order to increase people’s thermal comfort in cold weather, people usually use air conditioning and heating radiator to keep warm in the vast empty space of the entire building.3,4 However, it costs a considerable amount of energy; 47% of electricity consumption and 35% of greenhouse gas emissions are ascribed to heating systems globally.5,6 Consequently, considering this enormous portion of energy use, numerous efforts are being made to develop renewable energy such as solar energy,7 wind energy,8 and tidal energy9 which are all clean and renewable. However, these green energy resources are not always satisfied with energy demand due to their drawbacks such as low energy efficiency and large fluctuations by climate and environmental conditions. To meet the demands of practical applications, it is necessary to develop a functional material that not only keeps human warm but also saves energy more efficient.10 In this respect, an ideal energy-saving approach that is called personal thermal management was proposed, which can active heating and insulation directly based on humans. Currently, several active heating equipment such as airconditioning, electric furnaces, and radiator are widely used for adjusting the temperature in daily life. The use of active heating equipment in temperature adjustments has many advantages but serious economic and environmental draw© XXXX American Chemical Society

Received: Revised: Accepted: Published: A

January 3, 2019 February 21, 2019 March 4, 2019 March 4, 2019 DOI: 10.1021/acs.iecr.9b00041 Ind. Eng. Chem. Res. XXXX, XXX, XXX−XXX

Article

Industrial & Engineering Chemistry Research

Figure 1. Schematic illustration of fabrication of the multifunctional Cu-MES.

2. EXPERIMENTAL SECTION 2.1. Chemicals and Materials. Hydrazine hydrate (N2H4· H 2 O, 80%) and copper acetate monohydrate (Cu(CH3COO)2·H2O, 99%) were supplied by Sinopharm Chemical Reagent Co., Ltd. (Shanghai, China). All reagents were used as received without any further purification unless specially mentioned. Commercial melamine sponges were purchase from Guangsheng Sponge Plastic Co., Ltd. (Hangzhou, China). Distilled water was used throughout all experiments. 2.2. Preparation of Cu-MES. The copper coated melamine sponge was fabricated via in situ deposition of copper nanoparticles on the surfaces of melamine sponge. In a typical procedure, 2 mmol of copper acetate monohydrate was dissolved in 40 mL of distilled water in a beaker under magnetic stirring at room temperature. Then 1.6 mL of hydrazine hydrate (80%) was dropwise added into copper acetate solution to obtain uniformly dispersed copper nanoparticles. Afterward, the washed melamine sponge (4 cm × 4 cm × 2 cm) was immersed in above mixture solutions for 12 h at room temperature. Then copper coated melamine sponge was removed from the beaker and thoroughly washed with plenty of distilled water to completely remove reducing agent and other impurities. The cleaned copper coated melamine sponge was dried in a vacuum oven at 60 °C to obtain CuMES. Schematic illustration of fabrication of the multifunctional Cu-MES is presented in Figure 1. 2.3. Sample Characterization. The morphology of copper nanoparticle was characterized by high-resolution transmission electron microscopic (HRTEM, FEI, Tecnai 20, U.S.A.). The morphology of the raw MES and Cu-MES was analyzed by field emission scanning electron microscopy (JSM7800F FESEM, Japan). Surface functional groups of the raw MES and Cu-MES were recorded by a FT-IR spectrophotometer (Thermo Nicolet, NEXUS, TM) in KBr pellets in the range of 400−4000 cm−1. Phases of the raw MES and Cu-MES were characterized by an X-ray diffractometer (Shimadzu XRD-6100 instrument with Cu Ka radiation at 40 kV and 30 mA) and a Cu filter at 20 kV and 20 mA was used to obtain a chart recording in the 2θ range from 10 o to 80 o scanning step of 4°/s. Surface chemical analysis of Cu-MES with X-ray photoelectron spectroscope (XPS) on Thermo ESCALAB 250 XI to characterize the element valence states. 2.4. Thermal Management Properties. Thermal management properties were investigated by electric heating and

harmful carbon precursors hamper greatly their practical application. Therefore, how to construct the functional materials with both fast heating and insulation properties is of great importance. In the process of human skin heat loss, there are three main ways including heat convection, heat radiation, and heat conduction to adjust.18,19 For a typical indoor scenario, infrared radiation dissipation contributes to more than 50% of the total body heat loss.12,20 Hence, reducing infrared radiation dissipation is the most effective strategy for human body insulation.21 According to Boltzmann’s law, the infrared radiation, determined by surface properties (such as microstructures and chemical compositions) of materials, is related to the infrared emissivity and reflectivity of materials at any specified temperature and frequency.22,23 The control of surface emissivity of the wearable material would help the human body adapt to a wide range of ambient temperatures or physiological conditions.24,25 It provides an effective means for thermal management applications except for electric heating performance, because the human body is an obvious source of radiant heat. For instance, Hsu et al.26 demonstrate a dualmode textile based on regulatable characteristics both emissivity that can perform both passive infrared radiation heating and cooling by the different infrared radiation properties without any energy input. However, the surfaces of the material are easily contaminated by dust and other contaminants, resulting in the interference of infrared radiation.27,28 Therefore, a functionalized surface with selfcleaning properties, which renders materials more stable thermal management properties, is still desirable. In this paper, a multifunctional Cu-MES thermal insulation material with low infrared emissivity, excellent conductivity, as well as good self-cleaning properties is fabricated via simple reduction reaction and subsequent vacuum drying process. The Cu nanoparticles were tightly anchored in the melamine sponge, forming good conductive coating and low emissivity coating, which not only harvests heat from Joule heating but also prevent body heat loss. Based on the above properties, this study provides an energy saving and very convenient device to control temperature that can be employed as a stepping stone toward further understanding and designing of thermal management material. B

DOI: 10.1021/acs.iecr.9b00041 Ind. Eng. Chem. Res. XXXX, XXX, XXX−XXX

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Figure 2. TEM (A) and HRTEM (B) images of the copper nanoparticles.

Figure 3. Low-and high-magnification SEM images of raw MES (A, B) and Cu-MES (C, D).

infrared radiation processes. For an electric heating test, the asfabricated Cu-MES (4 cm × 4 cm × 2 cm) was connected with a power clip to each end of the sample, and subsequently continued power up with a power supply. The voltage was supplied using a DC regulated power supply (YB1730A) from 0 to 10 V. The heating properties of the Cu-MES were investigated by measuring the change of temperatures by time and power supply voltage. The thermal insulation properties of the Cu-MES are evaluated by the physical parameter of infrared emissivity, which were investigated at different positions on each sample by an IRE-2 Infrared Emissometer (Shanghai Institute of Technology and Physics, China). Thermal images of the raw MES and Cu-MES were taken by using an FLIR ONE PRO. 2.5. Self-Cleaning Properties. The self-cleaning properties were evaluated by the water droplet rolling behavior on the Cu-MES surface. For a self-cleaning property test, distilled water was chosen as the source for the sliding angle measurement, and the Cu-MES sample was fixed on a glass substrate. In a typical procedure, deionized water with a droplet volume of 5 μL was dispensed on the Cu-MES surface. The contact angle of the material was measured by remote computer-controlled goniometer system (FTÅ 200, Dataphysics Inc., U.S.A.) with Canon video camera by averaging over three different points at room temperature (25 ± 2 °C). Using a handmade setup, the rolling angle was measured by

this remote computer-controlled goniometer system (FTÅ 200, Dataphysics Inc., U.S.A.) via tilting the glass substrate. In addition, the dynamic process of water droplets on the copper coating surface was recorded using a Canon video camera. To investigate the hydrophobic stability of Cu-MES, the contact angle changes were tested within 10 days using the above device and system.

3. RESULTS AND DISCUSSION 3.1. Morphological Test. To investigate the morphology of copper nanoparticle coating on the surface of MES, the morphology and structure of the product was then investigated by TEM. The representative TEM images are presented in Figure 2, indicating that the copper nanoparticles are spherical or near spherical particles with nanoscales. In addition, it can be seen from Figure 2A that copper nanoparticles are interconnected with each other to a great extent. The interconnected copper nanoparticles are beneficial for efficient electronic transportation and enhance the electric heating of MES. The diffraction rings of the sample are composed of point-like discontinuous loops (Figure 2B), which is due to the insufficient powder diffraction effect. The corresponding selected-area electron diffraction (SAED) pattern of copper nanoparticles, as shown in the inset of Figure 2B, reveals the presence of a polycrystalline structure of copper nanoparticles, which is often obtained in rapid reduction methods. The C


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Figure 4. XRD patterns (A) and FT-IR spectra (B) of raw MES and Cu-MES.

Figure 5. Survey scans XPS spectra of Cu-MES (A). C 1s, O 1s, and Cu 3p XPS spectra of Cu-MES, respectively (B−D).

dispersed copper nanoparticles. The density copper nanoparticles coating deposited on the MES surfaces endow the Cu-MES with excellent conductivity and improve the electrical heating properties. The high magnification SEM image of CuMES is shown in Figure 3D. The densely packed copper nanoparticles were obviously observed on the surface of MES, indicating that copper nanoparticles have been successfully connected to the MES surfaces via in situ deposition method. Metal copper materials usually show extremely low infrared emission and high infrared reflectivity, which can reflect infrared radiation energy from heat source and reduce the loss of heat in the cold environment. The densely packed copper nanoparticles layer makes the fabricated Cu-MES potential applications in infrared energy saving. As can be seen in Figure 3C,D, there is no apparent difference in their appearances and morphologies except for the increase in surface roughness during the in situ deposition. 3.2. Structural Test. During the preparation of copper nanoparticles, the Cu2+ can be reduced to form metal copper by redox reactions, while other products such as CuO and

SAED patterns constituted by continuous rings and individual spots are indexed to be (111), (200), and (220) planes of a face-centered cube of elemental copper, in agreement with the XRD patterns of copper nanoparticles. A representative highresolution TEM image is shown in Figure 2B, indicating that the lattice spacing of copper nanoparticles is 0.21 nm, corresponding to (111) planes of the elemental copper. In the deposition process, the copper nanoparticles are attached onto the surfaces of MES. To further investigate the morphology and structure evolution of samples before and after copper nanoparticles deposition, the MES and Cu-MES were characterized by SEM, and the SEM images are shown in Figure 3. It can be seen in Figure 3A,B that the bare MES has an interconnected 3D hole-like structure with a diameter of approximately 60−120 μm and with a smooth skeleton of diameter of ∼7 μm, respectively. The highly open structure provides a structural basis for good breathability of the material, which is beneficial for copper nanoparticles deposition. Figure 3C,D shows the SEM images of the CuMES, indicating that the surfaces of MES are covered by evenly D


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Figure 6. Optical images showing static contact angle correspond to samples MES (A) and Cu-MES (B), respectively. Optical images of the drop rolling-off with rolling-off angle (C).

XPS measurement was conducted to identify the composition and chemical states of the Cu-MES. The survey XPS spectra of the prepared Cu-MES is shown in Figure 5. Survey scans of the sample identified the presence mainly of copper (Cu 2p), carbon (C 1s), nitrogen (N 1s), and oxygen (O 1s). A full XPS spectrum is shown in Figure 5A, which obtain binding energies of 283.4, 398.9, 530.1, and 936.4 eV revealing the existence of C, N, O, and Cu, respectively. The highresolution C 1s spectrum at 283.4 eV can be deconvoluted into two peaks with binding energies centered at 284.8 and 288.3 eV (Figure 5B) corresponding to the CO and the OC O atoms, respectively, which originate from carbon-containing molecules present in the MES. Furthermore, the highresolution O 1s spectrum displays one characteristic peaks at 530.6 eV (Figure 5C). For the Cu 2p spectrum (Figure 5D), two peaks at binding energies of 932.58 and 952.5 eV correspond to Cu 2p3/2 and Cu 2p1/2,31 respectively. Moreover, there are no other impurity peaks such as Cu 2+ and Cu +, and the results could indicate that the surface of CuMES was not oxidized after it exposed to open environment for some time. The result is strictly in accordance with the XRD analysis of the purity of copper, indicating the pure copper nanoparticles were embedded on surface of MES. In addition, the peaks of Cu 2p3/2 and Cu 2p1/2 are stronger than those of C 1s, N 1s, and O 1s, indicating the high levels of Cu nanoparticles on the melamine sponge. 3.3. Self-Cleaning Properties. The high contact angle and low sliding angle of material surfaces make them ideal for self-cleaning and thermal management application. The wettability behaviors and sliding angle of bare MES and CuMES are shown in Figure 6, demonstrating the excellent selfcleaning properties of as-fabricated Cu-MES. As shown in Figure 6A, water droplets dyed methyl blue permeated into MES completely and the surface only leaved circular dye marks, implying the hydrophilic character of the MES. However, it can be seen from Figure 6B that the spherical blue water droplets could stand on the surface of the Cu-MES, indicating the hydrophobic of the Cu-MES. To further verify the self-cleaning properties, the contact angle of water droplets on the surface of the Cu-MES are investigated comprehen-

Cu2O are undesirable because they can lead to potential issues such as high infrared absorption and hydrophilic property when used in infrared thermal management applications. In order to check the purity of the copper nanoparticles, the samples were systematically determined with powder X-ray diffraction. Figure 4 shows the XRD patterns for pristine commercial MES and Cu-MES obtained from copper nanoparticles deposition. As shown in Figure 4A, no distinct characteristic diffraction peaks were detected in the XRD pattern of pristine commercial MES, which showed that the raw melamine foam is an amorphous structure. By contrast, as the results are shown in Figure 4A. The XRD results show that the Cu-MES displays characteristic peaks at 2θ of 43°, 50°, and 74°, which are attribute to the (111), (200), and (220) crystalline planes of pure copper (JCPDS Card No. 040836).29 The characteristic diffraction of copper nanoparticles indicates the successful deposition of copper nanoparticles on the surfaces of MES. In addition, the sharp diffraction peaks reveal the high crystallinity of Cu-MES, which corresponds to the result of analysis of TEM. Moreover, no characteristic peaks of other impurities such as CuO and Cu2O are observed, indicating the pure copper nanoparticles were embedded on surface of MES. To better understand the mechanism of the infrared properties from the MES to the Cu-MES, FT-IR is used to analyze the chemical bonds in the MES and Cu-MES. Figure 4B shows the FT-IR spectra of the pristine commercial MES and Cu-MES obtained from copper nanoparticles deposition. The FT-IR spectrum of the MES shows the characteristic stretching vibration modes of CN and C−N on the triazine ring at 1542 cm−1 (CN), and 1329 cm−1 (C−N), respectively. The sharp absorption peak at 809 cm−1 is ascribed to triazine ring bending.30 Moreover, As shown in the Figure 4B, strong characteristic absorption bands at 997 and 3280 cm−1, which can be assigned to the twisted vibration peak of N−H and stretching vibration peaks of N−H. For Cu-MES, very few functional groups are observed, which can be explained by the infrared shielding effect of copper nanoparticles on the surface of MES. E


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Figure 7. Effect of number of days (A) and cycle number (B) on water contact angle.

Figure 8. Temperature change of Cu-MES and MES (A). Voltage-dependence of temperature in Cu-MES (B). Infrared images of Cu-MES applied a voltage of 7 V (C).

sively using contact angle measurements, and the results are shown in the inset of Figure 6. The contact angle for bare MES (inset of Figure 6A) could not be measured, showing its superhydrophilic property. After coating the copper nanoparticles, the as-prepared Cu-MES shows a stable water contact angle of 157.5 ± 2° (inset of Figure 6B). The Cu-MES not only has no hydrophilic groups, but also has a rough surface formed by copper nanoparticles, as confirmed by SEM and FTIR results. The rough surface without hydrophilic group do not allow the water molecules to soak into the Cu-MES, resulting in the formation of the superhydrophobic surfaces. The excellent superhydrophobic properties of Cu-MES can ensure the stable infrared radiation for thermal management applications. In addition, the process of a water droplet (5 μL) free falling to the Cu-MES was investigated, in order to inspect the water sliding behavior, as shown in Figure 6C. Obviously, the water droplets are not affected by any external force on the inclined surface and can be easily moved until they completely leave the surface with a water sliding angle of 15°. This means the Cu-MES is completely superhydrophobic without any sticky behavior, indicating good self-cleaning performance. Due to the superhydrophilic nature, the surfaces of bare MES are prone to be polluted and could not directly be

available for infrared radiation regulation. Efficient and stable self-cleaning properties for Cu-MES are essential for thermal management applications. Figure 7 shows the relationship between the contact angle and the number of days for Cu-MES the material placement process. As shown in Figure 7A, the contact angle slightly decreases from 158.95° to 155.15° with the number of days from 1 to 10, which suggests the asfabricated Cu-MES possessed excellent stability and could greatly facilitate use of Cu-MES for thermal management applications. The excellent elasticity would greatly further the practical application Cu-MES through a simple squeezing process. As is shown in insets of Figure 7B, the Cu-MES was extensively pressed using the slide glass and the Cu-MES could almost recover it initial height after released of the pressure. Additionally, the height of the Cu-MES decreased from 100% to 93.8% after 40 compression-recovery cycles, which suggests the as-prepared Cu-MES possessed excellent elasticity and could greatly guarantees its promising application. 3.4. Thermal Management Performance. The electric heating of Cu-MES can achieve effective and stable temperature control process, which can adjust ambient temperature to a thermally safe and comfort state. The temperature profiles of the Cu-MES plotted against heating time and voltage are F


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Figure 9. (A) Thermal images (down) and regular photos (up) of Cu-MES and MES. (B) The response time and heating transfer. (C) Schematic illustration of heat transfer model in the insulation process.

temperature to 40 °C in just 40 s. If the material is filled into clothes and a small mobile power source is built in, it can continuously convert electrical energy into heat energy which can transfer heat to the surrounding human body by radiation and conduction, in which both thermal radiation and conduction are beneficial. Combined with the infrared insulation properties of the Cu-MES, when the heat is generated enough, it can be stored well, which can increase thermal comfort. The low infrared emissivity of copper coating makes it ideal material to enhance the thermal insulation ability of Cu-MES. In order to investigate the thermal insulation properties of materials, the thermal images of a human hand with MES and Cu-MES attached on was studied, and the results are shown in Figure 9A. Both specimens are in thermal equilibrium on the palm before imaging with the palm temperature of 36.4 °C and atmosphere temperature of 18.0 °C. It is seen that the surface temperatures of raw MES are in the range 28.8−31.1 °C as detected by using an IR camera. By contrast, the surface temperatures of Cu-MES was lower, in the range of 27.1−29.1 °C, indicating the decrease of 1.7−2.0 °C compared with that of the raw MES. The infrared emissivity of MES and Cu-MES at wavelength of 8−14 μm is measured by infrared emissometer. The bare MES has a relatively high infrared emissivity value of 0.975, while the Cu-MES represent a lower infrared emissivity value of 0.724. The relationship between surface temperatures of Cu-MES with response time are shown in Figure 9B. The results prove that Cu-MES has a better thermal insulation property than of MES because of its lower emissivity, making the Cu-MES cooler in the thermal images. The heat transfer model of insulation process is illustrated in Figure 9C, and as a source of radiation, the human body continuously releases heat to the surrounding environment. In this case, most of the infrared radiation from the human hand can easily pass through the MES due to its high infrared

shown in Figure 8, which proves that the temperatures of CuMES can be controlled simply by heating time and voltage. The current required for electric heating is supplied by a DC regulated power supply, and the surface temperatures of the material are measured with a thermal couple in close contact with an error range of less than 5%. As shown in Figure 8A, there was almost no change in the surface temperature of untreated MES with increasing the heating time at DC power supply provides about 7 V. In contrast, the Cu-MES exhibits excellent electrical heating properties, and the surface temperature of the material rises from 18 to 40 °C in just 30 seconds. This is due to the extremely high electrical conductivity of CuMES compared with bare MES because the surface of Cu-MES is arranged with a dense layer of copper nanoparticles. Specially, for Cu-MES, a slight voltage supply nearly 7 V can already meet the normal requirement of the human body, and under normal circumstances, the maximum human body safety voltage is 36 V. To ensure safety of the human body, 7−7.5 V is enough for human thermal management application; however, a higher temperature can also be achieved. Figure 8B shows the relationship between surface temperatures of Cu-MES with supply voltage. It can be seen that the surface temperatures of samples increase with increasing the supply voltage. For example, the surface temperatures increased quickly to 58 °C at a supply voltage of 10 V in the first few seconds. As shown in Figure 8B, the surface temperature of the Cu-MES exhibits a nearly linear growth relationship, indicating the voltage-dependence of temperature in Cu-MES, and such good electrical heating properties could be applied to an extremely cold environment. Furthermore, all heating procedures are completed within the first 1 min and remain stable until power is removed. The intuitive electric heating map was obtained through an infrared thermal camera under a typical supply voltage of 7 V (Figure 8C). One can see that the surface temperature of Cu-MES is heated from room G



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emissivity value, which consumes a lot of body heat. In contrast, because the copper coating has a low infrared emissivity value, Cu-MES can effectively keep most of the body’s heat, resulting in keeping a human warm. Therefore, the results prove that the Cu-MES is an ideal insulation material.

AUTHOR INFORMATION

Corresponding Authors

*Tel./Fax: +86 511 88791800. E-mail: zhangtaochem@163. com. *Tel./Fax: +86 511 88791800. E-mail: [email protected]. ORCID

Tao Zhang: 0000-0001-9255-9802 Fengxian Qiu: 0000-0001-7475-7565 Notes

The authors declare no competing financial interest.

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REFERENCES

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4. CONCLUSIONS In summary, a multifunctional Cu-MES with low infrared emissivity, excellent conductivity, as well as good self-cleaning performance is fabricated via deposition of copper nanoparticles on the MES surfaces for thermal management applications. The results showed that copper nanoparticles are interconnected with each other to a great extent, which are beneficial for efficient electronic transportation and enhance the electric heating of melamine sponge. For active heating, the Cu-MES exhibits excellent electrical heating properties, the surface temperature of the material rises from 18 to 40 °C in just 30 seconds. In addition, the surface temperature of the CuMES exhibits a nearly linear growth relationship, indicating the voltage-dependence of temperature in Cu-MES. For infrared insulation, the bare MES has a relatively high infrared emissivity value of 0.975, while the Cu-MES represent a lower infrared emissivity value of 0.724. The Cu-MES has a better thermal insulation property than of MES because of its lower emissivity. For self-cleaning properties, the Cu-MES exhibits the superhydrophobic properties with a contact angle of 157.5° and a sliding angle lower than 15° that can ensure the stable electrical heating and infrared insulation properties for thermal management applications. Therefore, this work provides a facile way to design and fabricate novel multifunctional material with active heating, thermal insulation and superhydrophobic properties, which can be potentially used in various cold and complex environments and offers a new design consideration for thermal control.

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ACKNOWLEDGMENTS

This work was supported by the National Natural Science Foundation of China (21706100, 61705101 and 21878132) and the Natural Science Foundation of Jiangsu Province (BK20161362, BK20160491, and BK20160500). This research was also supported by China Postdoctoral Science Foundation (2018T110452 and 2017M621649), China Postdoctoral Science Foundation of Jiangsu Province (1701067C and 1701073C), Youth Talent Cultivation Program of Jiangsu University, Key Research and Development Program of Jiangxi Province (20171BBH80008), Society Development Fund of Zhenjiang City (SH2018009, SH2018011, and SSH20180140124), and the 333 High-Level Personnel Training Project of Jiangsu Province (BRA2016142). H


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Fabrication of Flexible and Superhydrophobic Melamine Sponge with

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