Superhydrophobic Coatings Prepared by the In situ Growth of Silicone

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Superhydrophobic Coatings Prepared by the In situ Growth of Silicone Nanofilaments on Alkali-activated Geopolymers Surface zihan Liu, xiaoqin pang, Kaituo Wang, xuesen Lv, and Xue-min Cui ACS Appl. Mater. Interfaces, Just Accepted Manuscript • Publication Date (Web): 04 Jun 2019 Downloaded from http://pubs.acs.org on June 5, 2019

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ACS Applied Materials & Interfaces

Superhydrophobic Coatings Prepared by the In Situ Growth of Silicone Nanofilaments on Alkali-Activated Geopolymers Surface Zi-han Liu, Xiao-qin Pang, Kai-tuo wang, Xue-sen Lv, Xue-min Cui* School of Chemistry and Chemical Engineering, Guangxi Key Laboratory of Petrochemical Resource Processing and Process Intensification Technology, Guangxi University, Nanning, 530004, China *Corresponding author email: [email protected]

ABSTRACT: As a highly hydrophobic and good environmental durable material, silicone nanofilaments (SNFs) have shown great advantages in the construction of superhydrophobic coatings. However, the synthesis of these materials has always been limited to the application of trifunctional organosilane monomers under the action of acidic catalysts. For the first time, long-chain polymeric hydrogenated siloxane-polymethyl-hydrosiloxane(PMHS) was used to synthesize rapidly silicone nanofilaments in situ under alkaline conditions. A dense silicone nanofilament coating was obtained by PMHS+geopolymer layer on a smooth iron sheet, and achieved by one-step brushing of PMHS on the surface of a just-solidified alkali-activated metakaolin-based geopolymer coating at 120 º C for an hour of sealed curing. This composite coating was followed by a superhydrophobic composite coating with a contact angle of approximately 161 degrees and a rolling angle of 2 degree. Consistent with this, laser scanning confocal microscopy and FESEM images show the presence of micro- and nanoscale features that enable the entrapment of air when exposed to water and excellent superhydrophobic properties. Because geopolymer material has good adhesion ability with metal, ceramic or other materials, the composite superhydrophobic coating is expected to be widely used. KEYWORDS: superhydrophobic coating, surface modification, silicone nanofilament, alkali-based geopolymer, in situ growth, mechanism, all-water-borne, large-scale INTRODUCTION

Superhydrophobic phenomena, known as the “lotus leaf effect”, refer to a water contact angle (the advancing contact angle) greater than 150 degrees for the contact angle hysteresis and the rolling angle of less than 5-10 degrees.1 This phenomenon can be explained by the "heterogeneous wetting regime" described by the Cassie Baxter model.2 Due to the high mobility of water droplets on these surfaces, the droplets above present perfect spherical structure and even a very slight tilting of the superhydrophobic object is sufficient to cause the drop to roll off. There is a consensus that the interaction between the effect of the binary collaboration of micronano structures and low surface energy is considered to be the cause of the stability of the superhydrophobic phenomena.3-7 Over the years, the preparation of superhydrophobic surfaces has been devoted to the construction of multi-scale 1

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roughness and the modification of surfaces by low surface free energy materials.8-15 Although the preparation methods of superhydrophobic coatings are various, the simple brushing process is always more conducive to meet its extensive applications, due to its high efficiency and economic advantages. Furthermore, the consequent gradual substitution of water-based coatings for existing solvent-based coatings is inevitable, as the former is irreplaceable for safety, green and health.16-18 However, due to the incompatibility between low surface energy materials and the water medium, it is always challenging to construct absolute water-based superhydrophobic coatings. As a green inorganic binder, geopolymer is made of metakaolin or other silicon-aluminium materials with silicon, aluminium and oxygen as the essential elements and undergoes dissolution, monomer reconstruction, polycondensation at lower temperature under the action of alkali activator.19 Up to now, this concept includes all amorphous and quasicrystalline three-dimensional network cementitious materials prepared from the mineral clay, solid wastes or synthetic silicon-aluminum powder which are aggregated by silica-oxygen tetrahedrons and alumina-oxygen tetrahedrons and contain abundant porous structure.20-23 They can resist high temperatures, chemicals, and friction and have characteristics of low permeability, rapid hardening, high strength, and strong bonding strength with metal, concrete, bricks, wood, and aggregate interfaces.24-29 Geopolymer coatings on metal substrates as thermal barriers and as protective coatings for concrete had been reported many times.24,28,29 However, a geopolymer is inherently hydrophilic because of the hydroxyl groups on its surface. In recent years, reactive organosilicon with hydrolytic groups (commonly included: -H, -Cl and -OR) has been widely used in the modification of water-based inorganic materials for their low surface free energy, fluorine-free and good chemical stability.15,30,31 The grafting modification of bifunctional and trifunctional silane to the substrate is also influenced by the reaction conditions, such as the alkyl structure and water content, which shows a flexible micromorphology and wettability.32 From this, a one-dimensional soft matter -- silicone nanofilaments (SNFs) with unusual wetting behavior is derived. These were first synthesized by chemical vapor deposition7 and liquid deposition33 using methyltrichlorosilane and vapor-phase plasma-induced polymerization34 using vinyltrichlorosilane by Stefan Seeger, Thomas J. McCarthy and De-ann E. Rollings et al. in 2006, respectively. Currently, these have been prepared on the surfaces of glass, ceramics, cotton fabric, silk, wood, nanofibrillated cellulose, etc.7,33,35-37 In addition to excellent hydrophobicity, they exhibit high transparency, environmental stability, good solvent resistance and chemical resistant over a certain range.38-40 Up to now, the preparation technology of silicone nanofilaments is still based on vapor-phase and liquid-phase deposition mainly,34,41-45 and only a few changes or improvements on this basis have been found in the follow-up study.46-47 There is no exception that the relationship between the formation of a filamentous structure and the film water layer enriched on the surface of the substrate was emphasized in these publications. Proper control of the humid environment and reasonable dosage of silane had always occupied the core of research for these materials.32,34,36,41,42,46 Recently, a droplet assisted growth and 2


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shaping mechanism (DAGS) has been proposed to explain the in-situ formation of nano- and microstructures composed of polysiloxane and other materials such as germanium oxide. It is believed that the nano and micro droplets formed on the surface of the substrate are likely to be the starting point for the formation of the 1D structure. The uniaxial extension of the filaments results from the spatial limitation of the water island.48-49 This develops a new strategie for in-situ chemical synthesis of nano/micron structures. However, there are still some limitations in the synthesis of existing silicone nanofilaments. For example, trifunctional silane has always been considered an indispensable precursor for generation of the fibrous structure.36,39,50 Moreover, the successful synthesis of the reported SNFs is confined to acidic conditions,36,46,50,51 which cannot be used to modify metals due to rapid corrosion. Nevertheless, the method has a great potential for reducing corrosion, fluid dynamic resistance and fuel consumption in marine coatings. In view of the superhydrophobic and anti-reflective properties of such coatings after annealing can be maintained stable in natural for at least one year, and it also performs outstanding in chemical durability tests of organic solvents, weak acids and alkalis, and neutral aqueous solutions.38,40 Therefore, it is necessary to explore the synthesis of silicone nanofilaments in neutral and alkaline conditions. In this article, we proposed a novel method to synthesize silicone nanofilaments in situ on the surface of freshly cured alkali-activated metakaolin-based geopolymer coatings. As far as we know, it was the first report on the successful synthesis of silicone nanofilaments under strong alkaline conditions. At the same time, we choosed polymeric hydrogen-containing silicone oil instead of trifunctional organosilicon small molecules as raw materials. The whole preparation did not involve the use of any volatile organic solvents. An all-water-borne superhydrophobic composite coating was achieved on iron sheet. The morphology, composition and wettability of the coating were characterized by Fourier Transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), Field-Emission Scanning Electron Microscope (FESEM), Energy-dispersive X-ray spectroscopy (EDS), Transmission Electron Microscopy (TEM), and confocal laser scanning microscopy (CLSM) and wettability measurements (CA,SA). The growth mechanism of the SNFs on the surface of the geopolymer was analyzed in detail. This work not only extends the selection of raw materials, preparation methods and application fields of silicone nanofilaments, but also provides new insights into the formation mechanism of the filaments. It also provides a simple strategy for the study of superhydrophobic modification of alkaline materials, and opens up more possibilities for the efficient preparation of all-water-borne superhydrophobic coatings, which reveals a true potential for application. EXPERIMENTAL SECTION Materials. Metakaolin was purchased from the Inner Mongolia Chaoyao Kaolin Co., Ltd. The chemical composition of metakaolin was SiO2, 49.13 %; Al2O3, 49.15 %; K2O, 0.22 %; Fe2O3, 0.42 %; TiO2, 0.73 %; CaO, 0.15 %; Na2O, 0.13 %; MnO, 3



0.0025 %; and MgO, 0.066 %, as determined using X-ray fluorescence (XRF). The liquid waterglass (sodium silicate solution Na2O · (SiO2)x · xH2O) was obtained from the Nanning Chunxu Chemical Co., Ltd and its mass composition is Na2O=9.2 %, SiO2=29.5 % and water=62.37 %. All the above two materials belong to industrial grade. The quartz sand with an average particle size of 75μm was provided by Xilong Chemical Co., Ltd.. Guanghua Polytron Technologies Inc. in Guangdong was the supplier of the chemical grade sodium hydroxide (96% pure) and poly(methylhydrogen)siloxane (PMHS with 99% purity and molecular weight 2500-3500 Da; CAS NO: 63148-57-2) with a hydrogen content of 1.6%. The high purity iron sheet (Fe≥99.99%) substrates (15 cm×7 cm×1 mm) were used as received from Guan Tai Metal Products Co., Ltd. in Shenzhen, Guangdong. Water colored with methylene blue with 98.5% purity (0.02% (w/w) in water, CAS NO:7220-79-3) was purchased from Tianjin Zhiyuan Chemical Reagent Co., Ltd. was used for visual purposes. Deionized water was used throughout this study. All the raw materials originated from China and were used as received without further treatment. Preparation of SNFs based on geopolymer coating. Firstly, the 100g liquid raw water glass (solid content 37.63%) with modulus 3.31M (M: SiO2:Na2O molar ratio=3.31) was modified as an alkali activator by adding 33.13g solid NaOH with 96% purity. After stirring, ultrasonic dispersion to complete dissolution and standing for 24 hours, the clarified modified water glass with a modulus of 1.3M was obtained, which was sealed and placed in a 22 º C thermostat for reserve. The SNFs-covered geopolymer coatings were fabricated as demonstrated in Figure 1. The mass ratio of the metakaolin, 1.3 M liquid waterglass and quartz sand was 1:1:8. Then, the geopolymer slurry was prepared by adding deionized water to adjust the liquid-to-solid ratio to 25%. A 20 g fresh geopolymer paste was coated evenly on a rectangular iron sheet of 15 cm×7 cm. The iron sheet was subsequently cured in an oven at 60 º C. After 20 min, the solidified slurry was removed from the oven and brushed 0.5 g PMHS by a brush as evenly as possible on the surface. All the quality control processes were completed by the analytical balance. It was then immediately placed in a cylindrical sealed glass container with an internal diameter of 18 cm and a height of 6 cm, and maintained at 120ºC for an hour. In this way, a geopolymer-based superhydrophobic composite coating with dense silicone nanofilaments was prepared. Characterization. A Hitachi SU8020(Japan) Field-Emission Scanning Electron Microscope (FESEM) equipped with Energy Dispersive Spectroscopic (EDS) was used to analyze the structures and components in detail at acceleration voltages of 10.0 kV and 20.0 kV, respectively. Before the test, all samples were fixed on copper conductive adhesive and coated with gold. In order to study the change of average surface roughness of coatings before and after modification, the Laser confocal scanning microscopy (CLSM, LSM 800Carl Zeiss, Germany) was used to study the three-dimensional microstructures of the coatings at three different locations on each surface, and then the average value was obtained. After initial scans, a robust Gaussian filter with a 4 μm cutoff was applied to the surface topography using the Mountains Map topography software (Digital Surf). Transmission Electron Microscopy (TEM, FEI TITAN ETEM G2 200 kV) was used to observe the fine 4


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morphology of the silicone nanofilaments at acceleration voltages of 300 kV. Scraping the surface of the coating with a stainless steel blade, the obtained powders were dissolved in ethanol and dispersed on copper grid after ultrasound for TEM observation. The coating sample of 2cm*2cm was cut by a cutter for the X-ray photoelectron spectroscopy (XPS) test. This measurements were carried out on an ESCALAB 250XI (Thermo Fisher Scientific, America) electron spectrometer. Fourier Transform Infrared Spectroscopy (FTIR) testing was obtained using a NICOLET iS10-Thermo scientific instrument for wavenumbers ranging from 4000 to 400 cm-1. Before testing, the coatings were purified in turn by acetone, ethanol and a large amount of deionized water, and dried in a vacuum drying box. Specimens were prepared by mixing 1 mg of nanocomposite coating/geopolymer coating prepared by scraping the coating surface with a blade with 100 mg of KBr, then pressed into thin slices using a tablet press. The wettability of the coatings before and after modification was achieved by using a DSA 100 contact angle instrument (KRUSS, Germany). Five different locations of each surface were selected to test static contact angle(CA) and rolling angle(SA) at ambient temperature. Their averages were reported. A 5 μL aliquot of deionized water was dropped onto the coatings. The droplet shape was imaged with a video camera and contact angle fitted by Laplace-Young method. Sliding angle also showed the heterogeneity of surface and was measured by injecting a 10 μL droplet on a surface and tilting the surface to find the angle of the surface to the horizontal plain when the droplet starts to slide. The BS224S analytic balance produced by Beijing Sedoris Instrument Co., Ltd. was used for weighing samples.

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Figure 1. A schematic diagram for the preparation of superhydrophobic composite coatings RESULTS AND DISCUSSION

Component Analysis of Composite Coatings. As Fig. 2A shows, the curves in (b) and (c) show absorptions at 2966 and 2904 cm-1 assigned to the stretching vibrations of the C-H bonds of the -CH3 groups, whereas another band, related to the bending deformation of Si-CH3 groups, is also observed at nearly 1260 cm-1.52 However, these should exist only in PMHS. The Si-H stretching vibrations of PMHS in (c) at 2166 cm-1 are a very strong indication there is significant amounts of active hydrogen in PMHS. However, the Si-H bond stretching vibration of the composite coating vanishes from sight, as there is no active hydrogen in the Si-O-Si main chain of the silicone nanofilaments, which can be attributed to the Si-H bond undergoing a hydrolytic reaction from the catalysis of the strong alkali, which are then convert to Si-OH groups, as shown in curve (b). The stronger peak at 3585 cm-1 is associated with the stretching vibrations of the -OH groups.52 These results suggest that PMHS has been successfully grafted onto the surface of the geopolymer by a simple coating. In addition, from the broad spectra scan of the composite coating (Figure 2B), we see that the peaks are mainly attributable to Si, O and C elements, meaning that the fibrous structure grafted on the surface is indeed derived from PMHS. （ A（

O 1s

（ B（

c

C 1s

3585

O（ KLL（

b

O 2s

2904

Si 2s Si 2p

a

Intensity(a.u)

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2966 2166

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3000

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1260

1500

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-1

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800

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Binding Energy(eV)

Figure 2. (A) FT-IR spectra of the: (a) geopolymer, (b) composite coating, and (c) PMHS. (B) XPS spectra of the SNFs-covered geopolymer coating.

Morphology and Wettability of Coating Surfaces. As shown in figures 3a and 3b, the surface of the modified geopolymer coating is covered by a large number of silicone nanofilaments with different aspect ratios. The contact angle of the coating increased from 22 degrees to 161 degrees and the rolling angle was only 2 degrees. It is difficult for a 3 μL droplet to adhere to the coating surface due to the excellent superhydrophobic properties of the coating, as illustrated in Figure 3i. Figure 3b shows the contact angle of the modified coating obtained by increasing the volume of the droplet to 5 μL. This can be attributed to the uniform coverage of the silicone nanofilaments on the surface of the geopolymer coating that allows more air to be stored in the network, which is made of interwoven filaments, resulting in the 6


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occurrence of the Cassie−Baxter wetting state. The dense fibrous coating shown in Figs.3e and 3f is similar to a "lawn" growing on the epidermal structure of the geopolymer "land". Correspondingly, due to the combination of the packed quartz sand and the natural porous structure of the geopolymer, figure 3c and 3d shows that the average surface roughness (Sa) of the local 1.277×1.277 mm2 range of the coatings before and after modification is 14.6μm and 10.8μm, respectively. The modification process of PMHS is helpful to improve the smoothness of the coating. This may be because the dense growth of SNFs fills in the macroporous defects partly from the geopolymer substrates. The dense fibrous coating shown in Figs.3e and 3f is similar to a "lawn" growing on the epidermal structure of the geopolymer "land". A stable superhydrophobic interface with a micronano hierarchical roughness is formed. We can observe the obvious silver mirror effect by immersing the modified geopolymer coating in an aqueous medium (Figure 3g), which is due to the total reflection of light in the air layer captured by the superhydrophobic interface, and the integrity of the plastron can verify the full coverage of the filament structure on the surface of the coating. Figure 3h shows that the water column falls on the surface of the composite coating to form water droplets and easily remove the surface silica fume, indicating that the coating has outstanding self-cleaning properties.

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Figure 3. FESEM images of the geopolymer-coated iron sheets before (a) and after (b) the PMHS treatment. The insets depict a water droplet (5μL) on each of the surfaces. Confocal laser scanning microscopy images (c) and (d) correspond to the 3D surface topography of the coatings before and after modification, respectively. FESEM images (e and f) showing the silicone nanofilaments grown on the rough geopolymer surface. (g) A photo of the composite coating submerged in water. (h) Self-cleaning was demonstrated as passing water droplets were easily able to carry away fouling powder spread over the monolith. (i) Photographs of the contact, deformation, and departure processes for a 3μL water droplet with respect to the fabricated composite coating surface and a 10μL water drop on a 2 degrees tilted SNFs-covered geopolymer coating.

The Formation Mechanism for Silicone Nanofilaments on the Surface of a Geopolymer. At present, the most commonly accepted theory on the reaction mechanism for geopolymers is the process of depolymerization, reconstruction and condensation proposed by Davidovits.19,53-55 The main steps include the breakage of Si-O and Al-O bonds in aluminosilicate minerals under alkaline conditions, the formation of silicon-aluminum complexes after the recombination of [Al(OH)4]- and 8


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[OSi(OH)3]- monomers, and a gel phase obtained by polymerization of the reconfigurable bodies under the presence of an alkali silicate solution. At the beginning of the reaction, the free water content decreased obviously, as it promoted the migration and transportation of ions and formed hydrates. However, at the polymerization stage, the free water was released gradually after the collision of the monomers to achieve the polycondensation reaction. Therefore, water can be deemed to play the main role in the transmission medium during the polymer reaction.20,21 With the gradual release of water, the system forms abundant pore structures. According to the in-situ observation of the micromorphology after curing for 10 min to 1.5 h by environmental scanning electron microscopy (ESEM), Zhang et al.56 At the initial stage of hydration, metakaolin particles were scattered, and there were a wide pore diameter distribution in the system. Some of the voids would be filled gradually with the extension of age. In the later stage, the colloids wrapped the particles thickly and the matrix became dense. In addition, high alkali concentrations are used as activators to break Si-O and Al-O bonds and release monomers in the preparation of geopolymers. However, only a few metal cations (Na+) are responsible for the construction of the geopolymer structure, which is designed to balance the negative charge generated by the four-coordinated [AlO4]- in the later stage reaction, and the bases actually act as a catalyst. Hence, excessive alkali exists in the system and throughout the reaction.57,58 The holes of the newly cured geopolymer coating are filled with strong alkaline aqueous solution. The tip of each channel for storing water is like a tiny reaction vessel. When the PMHS (with a structure

) is coated on the surface of a geopolymer coating, only a small of: amount of PMHS contacted with pore solution participated in hydrolytic polymerization in the tiny reaction vessel through adsorption. With the increase of hydrolysis products (called “PMHSO”), the PMHSO is repolymerized and precipitated. The nucleation sites of silicone nanofilaments are formed as shown in Figure 4. The reaction equation is described as follows:

When the coating is kept in a sealed environment at 120 degrees, water is released rapidly from the interior of the geopolymer and water vapour can quickly reach saturation in the sealed high borosilicate glass cabin. At this point, the liquid and vapor phases are in equilibrium. The water vapor partially diffused to the surface will condense at the interface of the new phase, thus ensuring the continuous water supply in the pore. According to Seeger et al,48 sustained supply of stable droplets is the key reason for the directed in-situ shaping of nano- and microstructures during chemical synthesis. The uninterrupted supply of water in the pore attracts more PMHS to participate in hydrolytic polymerization. Driven by vapor pressure and capillary force, 9



new solid phases formed are constantly pushed out of the pores, which lead to the growth of one-dimensional nanostructures. In other words, we believe that the natural pore in the geopolymer coating controls the size of water droplets that has been proved to be positively correlated with the formed diameter of the filaments.48 Therefore, these holes act as templates to direct the formation of the filaments to one-dimensional. These different pore sizes lead to diverse water content in each pore usually. The uneven distribution of the moisture in the rough surface may results in it covering a wide range of aspect ratios.48,59 As shown in the TEM images of the filaments in Figure 4, the diameters of the amorphous silicone nanofilaments are obviously inhomogeneous.

Figure 4. Transmission Electron Microscopy (TEM) images (a,b and c) of silicone nanofilaments.

In view of the fact that the water gradually discharged from the curing of the geopolymer is the only water source supplier in the system. The control of the rate of moisture transfer from the substrate to the surface, or controlling the water content in the surface, is the key to the in situ growth of silicone nanofilaments by a simple coating method in alkali-activated cementitious system. A brief summary of the formation mechanism for the silicone nanofilaments is as shown in Figure 5.

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Figure 5. The brief mechanism map for the formation of silicone nanofilaments on the surface of a geopolymer.

Subsequently, this viewpoint was further confirmed by comparing the surface morphologies of the coatings prepared under unsealed and sealed at 25, 60 and 120 degrees. As shown in Figure 6. The nucleation of SNFs can be observed under the sealing modification, and the formation of SNFs can hardly be seen in the open system. This is due to the fact that in the unsealed system, water diffuses to the surface and then evaporates into the air quickly, and almost no more water will stay on the surface to supply the growth of silicone nanofilaments. This is due to the fact that the unsealed system, in which water diffuses from the interior to the surface and then evaporates into the air quickly, which cannot ensure the uninterrupted supply of water. In addition, the growth rate of silicone nanofilaments at 120 º C was significantly higher than that at 25 º C and 60 º C by comparing the nanostructures formed under different temperature at sealing conditions. This can be attributed to the increase of curing temperature in the geopolymerization not only promotes the dissolution, but also accelerates the inter-precursor polymerization, which is conducive to the rapid release and diffusion of internal water to the surface. On the other hand, high temperature accelerates the hydrolysis of silane and promotes the rapid condensation of silanol, which is more conducive to the rapid growth of silicone nanofaliments.

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Figure 6. The FESEM figures of the composite coatings with different modification temperature and curing conditions, a, b, c, d, e, f were modified 30min for 25ºC non-sealed, 60ºC non-sealed, 120ºC non-sealed, 25ºC sealed, 60ºC sealed, 120ºC sealed, respectively.

Most notably, polymerization of the partially PMHSO with dissolved aluminosilicate monomers or segments in metakaolin can also occur during the precipitation of PMHSO molecule in holes. As seen from the EDS characterization of the bulk composition of silicone nanofilament in Figure 7, not only are the Si, O, and C elements from the PMHS found in the filament body but also a small amount of Al and Na elements, which are detected regularly in metakaolin. It is logical to draw that the condensation between the Si-OH/Al-OH existing on the surface of geopolymer and the PMHSO may always occurs during the self-crosslinking of the PMHS to form silicone nanofilaments. This may be different from the previous view that the growth of the silicon nanofilaments is initiated by the tip.41,44,45,47,48 The in-situ growth of this silicon nanofilaments can be attributed to the root, which triggers the "mushroom like" strand to stretch upwards successively to form the final one-dimensional nanostructure.

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Figure 7. Energy Dispersive Spectroscopic (EDS) spectra of the bulk of single silicone nanofilament. CONCLUSIONS

In summary, silicone nanofilaments were synthesized by a simple grafting modification of organosilicon on the surface of a geopolymer based on an alkaline environment. The geopolymer layer was first prepared on the surface of an iron sheet using the metakaolin precursor, quartz sand and liquid water glass as the raw materials. Then, the silicon nanafilaments can be grown in situ quickly by coating hydrogen containing silicone oil. A geopolymer-based superhydrophobic composite coating with dense bundles of filaments on the surface was successfully prepared. The results of FTIR and XPS confirmed that the fibrous structure originated from the hydrolytic self-crosslinking of the PMHS and was successfully grafted onto the metakaolin-based geopolymer substrates. In the meantime, the results of the contact angle measurements, rolling angle measurements, and water droplet nonstick tests indicated jointly the excellent superhydrophobicity and self-cleaning properties of the composite coating. The EDS and TEM characterizations of the nanofilament bulk composition together demonstrated that filaments growth gradually stretched upward and were initiated by the root. The water and alkali released gradually during high temperature sealed curing of geopolymer creates conditions for the growth of silicone nanofilaments. The natural pore structures in geopolymer act as templates, which limit the morphology of polysiloxane to one-dimensional. Therefore, we propose a novel, simple and efficient method for in situ synthesis of silicone nanofilaments. The surface superhydrophobic modification of alkali-activated cementitious materials was successfully realized. We believe that our results can provide a new strategy for designing the next generation of full-waterborne superhydrophobic coatings materials.

ASSOCIATED CONTENT Supporting Information The Supporting Information is available free of charge on the ACS Publications website at DOI: Preparation process of superhydrophobic composite coating. (AVI)

AUTHOR INFORMATION Corresponding Authors *E-mail: [email protected]. ORCID Xuemin Cui: https://orcid.org/0000-0003-1818-8470 Notes The authors declare no competing ﬁnancial interest.

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Graphical abstract


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Superhydrophobic Coatings Prepared by the In situ Growth of Silicone

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