Fast Healable Superhydrophobic Material | ACS Applied Materials

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A Fast Healable Superhydrophobic Material Liming Qin, Ying Chu, Xin Zhou, and Qinmin Pan ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.9b07563 • Publication Date (Web): 17 Jul 2019 Downloaded from pubs.acs.org on July 19, 2019

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ACS Applied Materials & Interfaces

A fast healable superhydrophobic material Liming Qin, Ying Chu, Xin Zhou, Qinmin Pan* (State Key Laboratory of Robotics and Systems, School of Chemistry and Chemical Engineering, Harbin Institute of Technology, Harbin 150001, P. R. China)

Corresponding author: Qinmin Pan No. 92, West Dazhi Street, Nangang District, Harbin 150001, P. R. China E-mail: [email protected]

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Abstract Self-healability is a crucial feature for developing artificial superhydrophobic surfaces. Although self-healing of microscopic defects has been reported, the restoration of severely damaged superhydrophobic surfaces remains a technological challenge. Here we report a robust superhydrophobic surface possessing ultrafast recoverability after catastrophic damage. The surface is fabricated via integrating its hierarchical texture comprised of Super P (a conductive carbon black) and TiO2 nanoparticles into a polydimethylsiloxane (PDMS) network cross-linked by dynamic pyrogallol-Fe coordination. In the presence of electrical trigger, the surface restores its macroscopic configuration, hierarchical texture, mechanical properties and wettability in one minute after multiple cuts in two halves or plasma etching. The restoration is attributed to the reconstruction of the multi-scales structures through the dynamic coordination. Application of the self-healable surface is demonstrated by a fast de-icing process. The present investigation offers a novel insight into the durability and reliability of artificial superhydrophobic surfaces against catastrophic damage, which has potential application in the fields including self-cleaning, anti-icing or advanced electronics, and so on.

Keywords: superhydrophobic surface, chemical damage, catastrophic damage, ultrafast restoration, pyrogallol-Fe coordination

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1. Introduction Superhydrophobic surfaces have important potential applications such as self-cleaning,1-3 oil/water separation,47

drag reducing8,9 and anti-icing.10-12 However, the practical application of superhydrophobic surfaces is

significantly impeded by their poor durability against mechanical or chemical damage. The poor durability is caused by either degradation or collapse of their delicate hierarchical texture during the practical application.13,14 In order to improve the mechanical durability, much effort had been devoted to rationally reinforcing the hierarchical structures of superhydrophobic surfaces.15,16 These attempts included covalently cross-linking of the hierarchical texture, as well as wrapping the texture with polymeric or rigid shells.17-19 Recently, bio-inspired self-healing was integrated in artificial superhydrophobic surfaces to fundamentally improve their robustness and reliability.20,21 Self-healable superhydrophobic surfaces had been fabricated by introducing self-healing polymer or migratable low-surface-energy material into their hierarchical textures.22,23 The resulting surfaces effectively recovered their superhydrophobicity after mechanical damages like scratching, abrading or scraping, exhibiting improved durability and good recyclability.24,25 The self-healing mechanism involves the release of low-surface-energy agents or the regeneration of topographic structures.26-28 Although successful recovery of microscopic defects has been achieved, the restoration of severely damaged superhydrophobic surfaces remains a big challenge. In particularly, the reported restoration strategies often involved complicated or time-consuming procedures (Table S1, Supporting Information). Therefore, there is still the lack of a facile strategy that fast restores multiscale structures ranging from macroscopic to molecular levels simultaneously after catastrophic mechanical or chemical damages. Here we report a robust superhydrophobic surface possessing ultrafast recoverability after significant mechanical or chemical damage. The superhydrophobic surface is fabricated by integrating its hierarchical texture into a polydimethylsiloxane (PDMS) network cross-linked by dynamic pyrogallol-Fe coordination. Once suffering from 3



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cutoff or plasma etching, the surface effectively restores its macroscopic configuration, hierarchical texture, mechanical properties and wettability within one minute by simply applying a DC power. The ultrafast restoration endows the surface with excellent anti-icing properties. The restoration strategy reported here is facile and has rarely been reported previously. The present investigation offers a new avenue to the design of robust superhydrophobic surfaces against catastrophic damage.

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2. Experimental section 2.1. Chemicals and Materials Gallic acid (GA) and TiO2 (~200 nm in diameter) were purchased from Aladdin Industrial Corporation. Ferric chloride (FeCl3) was purchased from Sinopharm Chemical Reagent Co., Ltd. (China). Potassium carbonate (K2CO3), thionyl chloride, and acetic anhydride were provided by Tianjin BASF Chem. Co., Ltd. (China). 1H,1H,2H,2Hperfluorodecyltriethoxysilane was purchased from Adamas Reagent Co., Ltd. Methanol, dichloromethane, and ethyl acetate were purchased from Tianjin Fuyu Fine Chemical Co., Ltd. (China). Amino-modified silicone oil (PDMSNH2) was provided by Guangzhou Xinguan Chemical Technology Co., Ltd (China). Tetrahydrofuran (THF) was purchased from Xilong Scientific Co., Ltd. (China). Pyridine was purchased from Tianjin Zhiyuan Chemical Reagent Co., Ltd. (China). Acetylene black (AB) and Super P (50 nm) were purchased from TIMCAL Graphite & Carbon (China). Pyridine and THF were dried before use, and the other chemicals were used as received. 2.2. Synthesis of acetic acid 2,3-diacetoxy-5-chlorocarbonyl-phenyl ester (GA-AC) GA (1.8 g) was first dried at 120 ℃ for 6 h and then dissolved in 5 mL of acetic anhydride at 20 oC. Later pyridine (4.3 mL) was added dropwise to the above solution. After stirring for 20 h, the resulting solution was poured into 45 mL of cold water. The acidity of the mixture was adjusted to pH 1 by hydrochloric acid (37 wt%) to produce white precipitate. The resulting solid was filtered, washed with ice water and dried at 80 ℃ to obtain 3.3 g 3,4,5triacetoxy-benzoic acid (GA-AA). The obtained GA-AA and 15 mL of SOCl2 were refluxed at 80 ℃ for 3 h. After the unreacted SOCl2 was removed by vacuum distillation, 3.2 g of yellowish acetic acid 2,3-diacetoxy-5chlorocarbonyl-phenyl ester (GA-AC) was obtained.29,30 2.3. Synthesis of gallic acid-grafted PDMS-NH2 (PDMS-GA) GA-AC (1.258 g), PDMS-NH2 (10.6 g) and 2 mL of pyridine were dissolved in 20 mL of THF. The resulting mixture was stirred at room temperature for 5 h. Then the solvents were removed by vacuum distillation to obtain 5



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GA-AC-grafted silicone oil (PDMS-GAA).29 The obtained PDMS-GAA was dissolved in methanol (20 mL) and CH2Cl2 (20 mL), and later 1.8 g of K2CO3 was added. After stirring at 25 oC for 1 h, the resulting mixture was filtered and the filtrate was vacuum distilled to produce raw gallic acid-grafted silicone oil (PDMS-GA). The resulting raw PDMS-GA was dissolved in a mixture of ethyl acetate (60 mL) and water (30 mL) under stirring. The ethyl acetate layer was separated, dried by anhydrous sodium sulfate, and vacuum distilled to obtain pure PDMS-GA. 2.4. Preparation of the PDMS-GA conductor First, acetylene black (0.3 g) and pure PDMS-GA (1.7 g) were dispersed in THF (40 mL) by ultrasonication. Thereafter FeCl3 dissolved in THF (20.2 mmol L1, 2.0 mL) was added to the above dispersion. After stirring at 25 oC

for 5 h, the resulting mixture was transferred to a mold and the solvent was removed by vacuum distillation to

produce a PDMS-GA conductor. 2.5. Fabrication of the superhydrophobic conductor TiO2 nanoparticles (2.5 mg) and super P (2.5 mg) were dispersed in ethanol (3.0 mL) and THF (1.0 mL) by ultrasonication. The resulting dispersion was dropped onto the above PDMS-GA conductor (surface area =5 cm2) at 50 ℃ in an oven. The obtained conductor was immersed in 5 mmol L1 ethanol solution of 1H,1H,2H,2Hperfluorodecyltriethoxysilane for 24 h and then dried at 50 ℃ for 6 h. 2.6. Self-healing of the superhydrophobic conductor The superhydrophobic conductor was cut into halves by a razor blade. The resulting pieces were contact and aligned for a geometric match. Later 10 V DC power was applied to the two ends of the matched pieces for one minute. The cut pieces coalesced into a single one. The healed conductor was subjected to tensile experiments and contact angle measurements. 2.7. Tensile experiments 6


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A piece of the original (or healed) superhydrophobic conductor (20 mm length  2 mm width  2 mm thickness) was used as a test sample. The two ends of the sample were fixed to the clips of a universal electromechanical testing machine (CREE 8007B). Then the sample was stretched at a rate of 50 mm min1 until it was broken. The tensile strength and breaking elongation of the sample were recorded. Mechanical healing efficiency (η, %) was calculated by the formula η = Sh/So × 100, where Sh and So are the tensile strength of the healed and the original samples, respectively. Each sample was tested for five times. 2.8. Chemical damage and self-healing of the superhydrophobic conductor A piece of superhydrophobic conductor was etched with O2 plasma (100 Pa, 40 W) for 50 s. The resulting conductor changed its wettability into superhydrophilicity. Then 10 V DC was applied to the superhydrophilic conductor for one min to restore superhydrophobicity. The etching and restoration were repeated for 10 cycles. 2.9. Delay freezing time test A piece of superhydrophobic conductor was placed on a cooling state at -15 °C and 30% RH. Later a droplet of deionized water (7 μL) was placed on the conductor. The freezing process of the droplet was monitored by a CCD camera and the freezing time was recorded. 2.10. Measurements of ice adhesion At first, a water droplet (25 μL) together with a copper ring (diameter = 2.5 mm) was frozen on a piece of superhydrophobic conductor at -15 °C and 30% RH for 12 min. The other end of the ring was fixed to the clip of a

highly sensitive microelectromechanical balance (DACT-21). The ring was moved upward at 2.0 mm min1 until it was detached from the conductor and the adhesive force (F) was measured. The ice adhesion (T, kPa) was calculated by the formula T = F/S, where S is the contact area between the conductor and the ice. 2.11. Electrothermal deicing experiments A piece of superhydrophobic conductor (25 mm × 25 mm × 3 mm) was placed on a cooling stage at -15 °C and 7



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30% RH. 0.5 g of ice was placed on the conductor. The conductor was applied with a 10 V DC power to remove the ice. The deicing process was recorded by a camera. 2.12. Characterizations Microscopic morphology was observed with a Zeiss Supra 55 scanning electron microscope. Nuclear magnetic resonance (NMR) was carried out on a Bruker (500 MHz). X-ray photoelectron spectroscopy (XPS) was conducted on a PHI5700ESCA. FT-IR and UV-Vis spectra were recorded by a Nicolet is50 and a UV-6100 spectrophotometer (China), respectively. Contact angle measurements were performed on an OCA 20 (DataPhysics) by using a water droplet of 4 μL. The droplet was placed at five positions of each sample. Contact angles were determined by the average of the measured values. Ice adhesion was measured by a highly sensitive microelectromechanical balance (DACT-21, DataPhysics). Oxygen plasma treatment was performed on a PDC-MG plasma cleaner (China). The DC power was supplied by MPS-3303 (China). The surface temperature of the conductor was monitored by an infrared thermal imaging camera (FLIRT360). Tensile experiments were performed on a universal electromechanical testing machine (CREE 8007B).

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3. Results and discussion 3.1. Synthesis of PDMS-GA At first gallic acid was grafted onto amino-modified polydimethylsiloxane (PDMS-NH2) through acylation to obtain PDMS-GA (Fig. S1, ESI).29-30 The grafting was confirmed by Fourier transform infrared (FT-IR) spectroscopy and nuclear magnetic resonance (NMR). Fig. S2a shows the FT-IR spectra of the original GA, GAAA and GAAC. Compared with those of GA, the peak at 3495 cm−1, which is assigned to the stretching vibrations of phenolic hydroxyl (OH), is not observed for GAAA and GACC. On the contrary, the vibrations of PhOC=O are observed for GAAA and GAAC at 1185 and 1786 cm1.31,32 The results indicate the reaction between phenolic hydroxyl of gallic acid and acetic anhydride. As for PDMS-GA, peaks attributed to the bending vibration of benzene ring (C=C) and stretching vibration of phenolic hydroxyl (OH) are located at 1600-1450 and 1232 cm−1,31,32 respectively, suggesting the grafting of pyrogallol group onto PDMS backbone (Fig. S2b). The chemical structure of PDMS-GA was further identified by 1H-NMR and 13C-NMR spectra (Fig. S3). The chemical shift at 4.9 and 7.28 ppm in the 1HNMR spectra were assigned to phenolic hydroxyl group (O-H) and benzene ring. Meanwhile, the chemical shift at 104,123.8,136 and 149.5 ppm were assigned to C atoms on the benzene ring. 33-35 3.2. Preparation of the superhydrophobic conductor Scheme 1 illustrates the fabrication of the self-healable superhydrophobic surface. The resulting PDMS-GA was then converted into a conductor (with an electrical conductivity of 38 S m1) in the presence of acetylene black (AB), conductive super P and FeCl3. Here super P acted as conducting agent, and AB was used to constructed hierarchical textures. The conductor has a water contact angle of 89 (Figure S4, Supporting Information). In this case, PDMS-GA chains were cross-linked by pyrogallol-Fe coordination. In contrast, the pristine PDMS-NH2 and AB could only form a viscous mixture (Figure S5, Supporting Information). Finally, the pristine PDMS-GA conductor was coated with super P (~50 nm in diameter) and TiO2 (~200 nm in diameter) nanoparticles through 9



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drop-casting to increase surface roughness and subsequently treated with hydrophobic 1H,1H,2H,2Hperfluorodecyltriethoxysilane (FAS-17). The resulting conductor was superhydrophobic by showing a water contact angle (WCA) of 154.9 ± 2.1o and a contact angle hysteresis (CAH) of 3.2 ± 0.5o (Figure 1a). Meanwhile, the superhydrophobic surface showed durability against extreme pH, ultraviolet light and seawater (Figure S6, Supporting Information).36

OH O

O Fe

O

O

OH

Scheme 1. Illustration for the fabrication of the self-healable superhydrophobic surface and its self-healing behavior. The microstructure of the superhydrophobic conductor was investigated by scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). The SEM images (Figure 1a-c) and X-ray energy-dispersive spectroscopy (EDS) maps display that the surface of the conductor is homogeneously covered with super P and TiO2 nanoparticles (Figure S7, Supporting Information). The nanoparticles aggregate to form a porous structure with a pore diameter of a few micrometers, exhibiting hierarchical micro- and nano structures (Figure 1b-c). EDS mapping also shows that super P and TiO2 nanoparticles are integrated in the PDMS-GA network since Si and Fe elements are also detected on the surface (Figure S7, Supporting Information). The integration is due to the 10


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coordination between pyropollollic moiety and TiO2 nanoparticles,37 which plays an important role in the stability of the hierarchical texture of the conductor. The superhydrophobic conductor also showed a WCA above 154° after tape-peeling test. However, the abrasion resistance of the conductor should be improved (Figure S8, Supporting Information). XPS spectra show that fluorinated siloxane is homogeneously coated on the conductor via the hydrolysis of FAS-17 (Figure S9, Supporting Information). Therefore, the hierarchical texture together with lowsurface-energy siloxane coating account for the superhydrophobicity of the conductor.38,39 It was revealed that the hierarchical texture of the conductor was affected by the mass ratio of super P to TiO2 nanoparticles (Figure S10, Supporting Information). Increasing the super P fraction resulted in a conductor with high WCA and low CAH (Figure 1d).

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Figure 2. (a) Photographs show cutoff and self-healing of the superhydrophobic conductor. (b-c) SEM images of the healed region (red rectangles). Inset is a water droplet placed on the healed region. (d) Stress-strain curves of the original and healed superhydrophobic conductors. (e) Variation of WCA after multiple cut/healing cycles. Inset is the tensile stress and mechanical healing efficiency during the cycles. The superhydrophobic conductor was able to quickly restore its macroscopic configuration, microstructure and wettability after severe mechanical damage. Here the conductor was first cut into halves with a razor blade and the resulting pieces were aligned for a geometric match. The aligned pieces were then applied to a 10 V DC power.

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Only one minute later, the halves coalesced into a single one that could support its own weight, showing effective healing of macroscopic configuration. Interestingly, the healed conductor also recovered the superhydrophobicity simultaneously because a water droplet quickly rolled off from the healed region (Figure 2a, Movie 1 of Supporting Information). The restoration of the conductor was confirmed by SEM observations (Figure 2b-c). Although the

healed region has a distinct boundary due to the malposition of the halves, there are almost no cracks at the region, suggesting effective recovery of the microstructure. The healing of the conductor was further supported by uni-axis tensile experiments. Figure 2d is the tensile stress-strain curves of the conductor before cut and after healing. The healed conductor shows a tensile strength of 467.2 ± 7 kPa, exhibiting a mechanical healing efficiency of 86.4% when compared with that of its original equivalent (540.8 ± 8.7 kPa). In addition, the conductor also recovered about 73.3% of the breaking elongation after healing. The results demonstrate that our superhydrophobic conductor effectively restores its macro- and microscopic structures, mechanical properties and wettability even after severe damage like cutoff. Owing to the excellent self-healability, the conductor was able to efficiently recover its superhydrophobicity and mechanical properties during six cycles of cut/healing (Figure 2d, Figure S11, ESI). It still kept a WCA above 153 and a tensile strength up to 448.7 ± 8.7 kPa after the 6th restoration (Figure 2e). We also found that the restoration and mechanical properties of the conductor also depended on the content of AB and FeCl3 (Figure S12, Supporting Information). Heat treatment could also result in self-healing of the conductor (Figure S12, Supporting Information). To the best of our knowledge, this is the first report on ultrafast restoration of a superhydrophobic material after severe damage through a simple electrical trigger, while avoiding conventional stimuli like light, pH and organic solvents.

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Figure 3. (a) Infrared thermal image of the superhydrophobic conductor after applying 10 V DC for one minute. (b) Temperature change of the superhydrophobic conductor over time at different DC voltages. (c) UV-vis spectra of gallic acid/Fe3+ complexes at different temperatures in pH 7 water. (d) DSC curve of the neat PDMS-GA elastomer. (e) Illustration schematics the restoration mechanism of the superhydrophobic conductor. The restoration of the superhydrophobic conductor was found be associated with the Joule thermal effect. At first, the electrical conductivity of the superhydrophobic conductor was measured at room temperature (Figure S13, 14


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Supporting Information). On the whole, the conductivity raises with the increase of the content of AB and super P, while it decreased by increasing TiO2 fraction. The maximum value of 40 Sm1 is obtained when the content of AB and mass ratios of super P/TiO2 is 15 wt% and 1:1, respectively. To evaluate the Joule thermal effect of the superhydrophobic conductor, we applied a DC power to its ends and the surface temperature was recorded by an infrared thermal imaging camera. Figure 3a is a typical infrared thermal image recorded for the conductor. It quick increases its surface temperature to 155 oC after applying 10 V DC for 60 s. The temperature increase is strongly dependent on the voltage and time. As shown in Figure 3b, either increasing voltage or prolonging time results in a higher surface temperature. As expected, the superhydrophobic conductor quickly decreased its surface temperature to ~30 oC after power off. Therefore, the temperature of the conductor could be readily controlled through power on or off (Figure S13c, Supporting Information). Note that the elevated temperature did not deteriorate the wettability of the superhydrophobic conductor (Figure S14, Supporting Information). Even after storage at 150 oC for 24 h, the conductor kept its superhydrophobicity unchanged, exhibiting good thermal durability. The restoration was also revealed to originate from the temperature dependence of dynamic pyrogallol-Fe coordination. As described above, the broken conductor fast restored itself at 155 oC. This means that the chains of the PMDS-GA network exhibit high mobility at elevated temperature, although they are cross-linked by pyrogallolFe coordination. To investigate the mechanism for the high mobility, we conducted UV-vis spectroscopy on an aqueous solution of gallic acid and FeCl3 at 25-90 oC. The solution was adjusted to pH 7 in order to simulate the acidity of the PDMS-GA network (Figure S15, Supporting Information). Figure 3c and Figure S15c clearly shows absorptive peaks at ~550 nm, indicating the formation of bis-pyrogallol-Fe complexation.37,40 Interestingly, the intensity of the peaks decreases as the temperature is increased from 25 to 90 oC. The reduced intensity suggests that the coordination between gallic acid and Fe3+ is weakened at elevated temperature. The peak recovers its original intensity again once the temperature backs to 25 oC. The results confirm that the bis-pyrogallol-Fe 15



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coordination is temperature dependent and exhibits dynamic nature. Moreover, the PDMS-GA network exhibits a low glass-transition temperature (Tg) of -4.6 oC (Figure 3d). Clearly low Tg together with the dynamic coordination endow the PDMS-GA network with good mobility at elevated temperature. Therefore, the ultrafast restoration of the superhydrophobic conductor is attributed to the dynamic nature of the PDMS-GA network at elevated temperature. Once the aligned halves were applied to the DC power, their bulk temperature quickly raised to 155 oC due to the Joule thermal effect. The elevated temperature weakened the coordination between pyrogallollic moiety and Fe3+, which allows part PDMS-GA chains to be released from the cross-linked network. These free PDMS-GA chains were able to move across, entangle or interpenetrate at the contact interface. Then new bis-pyrogallol-Fe complexation forms between the entangled chains, resulting in the restoration of the broken PDMS-GA network. Since TiO2 and super P nanoparticles are integrated in the PDMSGA network, the restoration will induce the recovery of the broken hierarchical textures (Figure 3e). The superhydrophobic conductor also fast recovered its wettability after chemical damage (Figure S16, Supporting Information). Here the superhydrophobic conductor was etched by oxygen plasma for 50 s. The etched conductor became superhydrophilic with a WCA of ~0. The superhydrophicity is ascribed to the formation of oxygen-containing moieties in the presence of highly reactive oxygen radicals and ions.41,42 However, the superhydrophilic conductor returned to superhydrophobicity (WCA = 154.9) when it was applied to a 10 V DC for one min. The recovery of superhydrophobicity is due to the weakened coordination between PDMS-GA chains at elevated temperature, which allows the FAS-17 trapped in the hierarchical texture to migrate to the outer surface.20,21 The migration effectively covers the oxygen-containing moieties and thus minimizing the surface energy of the conductor.43,44 The migration was confirmed by the content of F and O elements recorded for the etched and healed samples, respectively (Figure S17, Supporting Information). In this case, the conductor could switch between superhydrophobicity and superhydrophilicity for at least 10 cycles, showing excellent self-healing capability. 16


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Moreover, the microstructure of the conductor did not change even after 10 cycles of switch, as evidenced by the SEM image in Figure S16b of Supporting Information. 3.4. Anti-icing property of the superhydrophobic conductor Application of the superhydrophobic conductor was demonstrated by a de-icing process. At first, a water droplet (7 L) was placed on the conductor at -15 oC and RH 30% to observe its freezing process. Figure 4a shows that the water droplet freezes into an ice bead after cooling for 430 s. The delay time is much longer than that on the pristine PDMS-GA conductor (i.e., 100 s, Figure S18 of Supporting Information). The ice adhesion of both conductors was also measured to evaluate their anti-icing properties (Figure S19, Supporting Information). Generally, the ice adhesion of the superhydrophobic conductor is much lower than that of its pristine counterpart. The good anti-icing property lies in the air tapped in the hierarchical texture.10-12 The air cushion largely reduces the contact area between the water droplet and the superhydrophobic conductor, which slows down heat transfer at the interfaces.45-47 It was found that both delay time and ice adhesion of the superhydrophobic conductor was significantly affected by the mass ratio of super P/TiO2. Increasing the fraction of TiO2 nanoparticles resulted in a shorter delay time and a higher ice adhesion. Taking advantage of low ice-adhesion and the Joule thermal effect, we could fast remove ice from the superhydrophobic conductor by applying 10 V DC power for only 40 s (Figure 4b, Movie 2 of Supporting Information). More importantly, the superhydrophobic conductor also exhibited long delay time and low ice adhesion even after five cycles of cut/healing, showing excellent robustness and reliability for anti-icing application (Figure 4c-d).

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3

4

5

Healing cycle

Figure 4. (a) CCD camera records the freezing of a water droplet on the superhydrophobic conductor. (b) Photographs show the removal of ice from the superhydrophobic conductor by applying a 10 V DC power. The conductor has a size of 25 mm × 25 mm × 3 mm. Variation of (c) freezing time and (d) ice adhesion of the conductor after multiple cut/healing cycles.

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4. Conclusions In summary, this study demonstrated ultrafast restoration of macro- and microscopic structure, mechanical properties and wettability of a severely damaged superhydrophobic surface. It still kept a WCA above 153 and a tensile strength up to 448.7 ± 8.7 kPa after the 6th restoration. The capability allowed the surface to possess excellent anti-icing properties after multiple cutoffs. The ultrafast restoration is mainly attributed to dynamic nature of pyrogallol-Fe coordination that allows the broken PDMS-GA network to reconstruct at elevated temperature. The reconstruction thereafter induces the recovery of the multiscale structures ranging from macroscopic to nanometer levels. Moreover, it also completely restored the superhydrophobicity even after 10 cycles of plasma etching/heating. Although the abrasion resistance of our superhydrophobic conductor should be improved, the present finding provides a regenerative-like strategy to the durability and reliability issues of artificial superhydrophobic surfaces against catastrophic damage.

Supporting Information Synthetic route and characterizations of PDMS-GA, SEM images of the PDMS-GA conductor and the superhydrophobic conductor, optical image of the mixture of PDMS-NH2 and AB, water contact angle of the superhydrophobic conductor under extreme pH and ultraviolet conditions, EDS mapping and XPS spectra of the superhydrophobic conductor, tape-peeling test on the conductors, CAH and SA after multiple cut/healing cycles, stress-strain curves, electronic conductivity, infrared thermal image and thermal stability of the superhydrophobic conductors, UV-vis spectra of gallic acid and PDMS-GA, water contact angle and EDS plot of the superhydrophobic conductor after O2 plasma etching and self-healing, freezing process on the pristine PDMS-GA conductor, freezing time and ice adhesion of the superhydrophobic conductors, summary of typical self-healing superhydrophobicity reported in literatures. The self-healing process of the superhydrophobic conductor (Video S1).

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The fast remove ice from the superhydrophobic conductor (Video S2).

Acknowledgements The work was supported by National Natural Science Foundation of China (51473041) and the Foundation for Innovative Research Groups of the National Natural Science Foundation of China (51521003).

Author Contributions Liming Qin and Ying Chu contributed equally to this work

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OH O

O Fe

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Fast Healable Superhydrophobic Material | ACS Applied Materials

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