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Surface & Coatings Technology xxx (2015) xxx–xxx

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Surface & Coatings Technology

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Achieving to a superhydrophobic glass with high transparency by asimple sol–gel-dip-coating method

Toktam Rezayi a, Mohammad H. Entezari a,b,⁎a Sonochemical Research Center, Department of Chemistry, Ferdowsi University of Mashhad, 91779 Mashhad, Iranb Environmental Chemistry Research Center, Department of Chemistry, Ferdowsi University of Mashhad, 91779 Mashhad, Iran

⁎ Corresponding author at: Sonochemical Research CeResearch Center, Department of Chemistry, Ferdowsi UMashhad, Iran.

E-mail addresses: [email protected], moh_entezari@y

http://dx.doi.org/10.1016/j.surfcoat.2015.06.0150257-8972/© 2015 Elsevier B.V. All rights reserved.

Please cite this article as: T. Rezayi, M.H. Ent

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Article history:Received 16 March 2015Accepted in revised form 9 June 2015Available online xxxx

Keywords:Sol–gel-dip-coating methodSuperhydrophobic surfacesFluorine doped tin oxideThrimethylchlorosilaneTransparency

Superhydrophobic surfaces (SHS) require a combination of surface roughness and low surface energy. Coatingthe surface with a thick layer frequently leads to loss of its clarity. The deposition of fluorine doped tin oxide(FTO) by sol–gel-dip-coating method was used to get a desirable roughness and trimethylchlorosilane (TMCS)was used for the reduction of surface free energy. In addition, the optimization was carried out on the importantvariables such as F:Sn ratio in the starting solution, TMCS concentration and time of immersion in the TMCSsolution. It was discovered that the highest water contact angle (WCA) and lowest sliding angle (SA) on thesuperhydrophobic glass substrate was achieved under optimum conditions. The SHS prepared by this approachhas shown a high transparency and significant stability against an acidic environment. Structural analysis wascarried out byX-raydiffraction (XRD), attenuated total reflectance in conjunctionwith Fourier transform infrared(ATR-FTIR), and scanning electron micrograph (SEM). Furthermore, determination of the composition of thesurface was conducted by energy dispersive X-ray analysis (EDX). Finally, the optical transparency of SHS hasbeen confirmed using UV–vis spectrophotometer.

© 2015 Elsevier B.V. All rights reserved.

1. Introduction

Surfaces with WCA larger than 150 °C are known as SHS. Thesesurfaces fall into two categories based on the value of SA. One class isnamed as low adhesive-SHS (Cassie state) with low SA and anotherclass is called high adhesive-SHS (Wenzel state). In the latter case,surface has high SA and water droplets are attached to the surface [1].Materials with high WCA and high adhesive force are of interest andcan be used in the liquid transportation [2].

In the other side, because of numerous applications of low adhesive-SHS as water repellency, anti-corrosion and self-cleaning, these surfaceshave attracted much attention [3–5]. Specially, the superhydrophobicglass surfaces have generatedwidespread interest due to their extensiveapplication in the solar panel illumination glass, car windshield, and soon [6]. Generally, for having SHS, two-step approaches are necessary tocarry out; in which firstly surfaces with hierarchical roughness are fabri-cated and then special chemicals with low surface energy are depositedonto the created rough surfaces [7].

In order to acquire suitable roughness various deposition methodshave been used such as, electrospinning, hydrothermal synthesis,

nter, Environmental Chemistryniversity of Mashhad, 91779

ahoo.com (M.H. Entezari).

ezari, Surf. Coat. Technol. (20

lithographic approach, layer-by-layer assembly and chemical deposition[8–12]. Reduction of surface free energy is possible by using low surfaceenergymaterials such as silanes which are fluorinated [13]. Themajorityof maintained deposition methods are appropriate to definite types ofmaterials. Therefore, achievement to low-priced and largely applicableSHS coatings is a methodological challenge [14].

In this paper sol–gel-dip-coating (SGDC) method has been used inacquiring proper roughness as well as superhydrophobic property onglass substrate. SGDC approach possesses a number of superiority incomparison with other deposition methods. For example, it is inexpen-sive, simple, using elevated purity preliminary materials, and coating iseasier for the substrates which are bulky and complex [15]. There areseveral attempts related to superhydrophobic glass creation. Mahadikasynthesized a highly transparent superhydrophobic glass substrateusing SiO2 deposition by SGDC and modification with TMCS hexanesolution [16]. In anotherwork,Wang [17] has used a very simple immer-sion method for TiO2 deposition and modification with stearic acid. Thesynthesized superhydrophobic glass does not demonstrate an acceptabletransparency. In another word, a turbid superhydrophobic glasssubstrate has been resulted.

In the present work, fluorine-doped tin oxide (FTO) film depositionand TMCS modification have been utilized for highly transparentsuperhydrophobic glass creation. It must be denoted that SHS withhigh transparency is an extremely significant characteristic. Since SHSneed high roughness, the preparing of transparent SHS is very difficult.In addition, a thick covering on the substrate will be accomplished by

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2 T. Rezayi, M.H. Entezari / Surface & Coatings Technology xxx (2015) xxx–xxx

light scattering as well as loss of its transparency. In conclusion, thepracticable application of SHS on substrates with transparent propertysuch as glass is restricted [17].

Tin-oxide is a transparent material with a broad band-gap. For im-provement of its electrical and optical properties, tin oxide doping wasdone with fluorine (FTO), antimony (ATO), cadmium andmolybdenum[18–21]. FTO film is broadly used in optoelectronic fields for examplestylish windows, solar cells, and displays [22]. There are several articlesrelated to synthesis of FTO for conductivity and optical characteristics.For example, Banerjee et al. [15] synthesized FTO film with sol–gelmethod and examined electrical and optical properties of the resultedfilms. In other work, Purwanto et al. [22] fabricated FTO films usingflame assisted spray deposition method and studied the transparencyand electrical properties of the synthesized films.

In spite of these attempts, there are no reports about the applicationof FTOfilms in the creation of transparent superhydrophobic surfaces. Inthis paper, FTO films with cost effective sol–gel approach have beenprepared on glass substrate. This deposition makes suitable roughnessthat is essential for having superhydrophobic property. Besides, startingmaterials are available, inexpensive, and in conjunction with a straight-forward technique, this method can be used for the large-scale surfaces.Reduction of surface free energy has been conducted via TMCS. Theresulted SHS glass show WCA equals to 156.58° ± 1.51° and SA of(25.33° ± 2.02°). This state is nearly close to low-adhesive-SHS mode.Superhydrophobic glass fabricated with this method demonstratedremarkable transparency especially in the visible region. The hightransparency of the resulted superhydrophobic glass is the majorpoint of the current work. This property makes the superhydrophobicglass undistinguishable with the bare one.

2. Experimental

2.1. Materials and methods

Stannous chloride (SnCl2 2H2O, 95%, Bdh), hydrogen fluoride (HF,40%, Merck), isopropyl alcohol (IPA, 99%, Fluka), ethanol (96%, Merck),thrimethylchlorosilane (TMCS, 99%, Merck), hydrochloric acid (HCl,37%, Merck), and potassium hydroxide (KOH, 85%, Riedel) were usedas received without any purification.

The sol, which is necessary for the creation of desirable roughness onglass substrate, was made according to the literature [15]. In brief,distinct amounts of SnCl2 and HF were dissolved in 50 mL of IPA toform several solutionswith different HF:SnCl2 ratios in starting solution(0:1, 10:1, 20:1, and 30:1). The concentration of SnCl2 was 0.01M in allsolutions. The prepared solutions appeared turbid initially and afterstirring and refluxing for 1 h at 70 °C clear colorless solutions wereobtained. These solutions remained at room temperature for 2 h toform the sol.

The glass substrates were cleaned using distilled water, ethanol andIPA to remove any pollutant from them. After drying at 80 °C for 5 min,the cleaned substrates were vertically dipped into and then withdrawnslowly at the rate of 1.3mm/s from the solutions. The dipping and risingwere conducted for 15 times and between the two consecutive dippingthe substrate along with the sol was dried at 80 °C to have a rapidgelatin. Finally, the substrates were annealed at 350 °C in air for45 min. The annealing was carried out to sinter and solidify the FTOcoating and advance the strength of the film [23]. Apart from hardeningthe coating, the presence of oxygen in air can oxidize the deposited film[24]. Therefore, the creation of SnO2 can be completed in annealing pro-cess. However, due to the presence of F− and its substitution with O−2,the existence of Sn–O and SnF2 is possible.

In this step, the glass substrate with enhanced roughness wasconcluded. For surface energy reduction, the resulted substrates wereimmersed into TMCS ethanol solution with optimized concentrationfor distinct time. The glass substrates were dried at 80 °C for 10 min.

Please cite this article as: T. Rezayi, M.H. Entezari, Surf. Coat. Technol. (20

2.2. Characterization and measuring the contact angle

The FTIR spectra of the glass substrateswere obtainedwith attenuatedtotal reflection (ATR) in conjunction with Fourier-transform infraredspectrophotometry (Shimadzu-IR-460 spectrometer). The number ofscanswas 128 and thewavenumber rangewas 400–4000 cm−1. Further-more, the crystal used for ATR analysis was ZnSe.

The morphology of the substrate has been investigated using scan-ning electron microscopy (LEO 1450 VP, Germany). Another usefultechnique for morphology assessment is atomic force microscopy. TheAFM device (model no. 0101/A, Iran) has been used for this purpose.The images were captured under ambient temperature using nanoprobe cantilever in non-contact mode. The elemental analysis of the re-sulted surfaces has been assessed by energy dispersive X-ray (EDX,EXL2). The crystallite investigation of the resulted film was conductedusing an X-ray diffractometer (XRD, X'Pert ProMPD). The optical trans-mittance was measured by a spectro UV–vis double beam PC scanningspectrophotometer (UVD-2950).

The contact angles weremeasured using a homemade contact angleinstrument. Water droplets (10 μl) were dropped with a micro syringecarefully onto the sample surface. Images were captured with camera(Canon SX200, Japan) and then were analyzed using MATLAB softwarefor acquiring WCA. The SA measurement was conducted with a simpledesigned device which has a movable plane for tilting the glasssubstrate until water droplet starts to roll off. Since the plane cannottilt more than 90°, the highest value of SA will be 90°.

3. Results and discussion

3.1. HF:SnCl2 ratio optimization

Generally, the glass substrate is hydrophilic with WCA nearly to46.06° ± 2.10°. After TMCS modification, the WCA increased to73.74° ± 1.34°. This means that the surface energy reduction is notsufficient to achieve a SHS of glass. Fig. 1 demonstrated the waterdroplet on glass substrate before and after TMCS modification.

At the outset, the effect of HF:SnCl2 ratio in the initial solution hasbeen examined on WCA values for glass substrate. The range of ratioin the starting solution falls in 0:1 to 30:1. For all substrates after dippingin cited solutions, the surface free energy decreased by immersion inTMCS ethanol solution (10% v/v) for 24 h. This outcome can be seen inFig. 2.

It is clear that with addition of HF to reach the ratio = 10:1, WCAincreased significantly up to 156.58° ± 1.51°. In addition, SA has thelowest value at this ratio (25.33° ± 2.02°). For other ratios, the SA isas high as 90°. For the ratios of 20% and 30%, the water droplet has anearly spherical shape and attaches to the surface. For assurance, theexperiment has been repeated three times and the average valueshave been reported. It should be noted that for obtaining HF:SnCl2ratio equal to zero, a distinct amount of SnCl2 has been dissolved in50 mL IPA without addition of HF.

Fig. 2 reveals that the ratio equals to 10:1 can be an optimum ratiofor reaching surfaces with high WCA and low SA.

3.2. Optimization of TMCS concentration and time of immersion

After finding the optimum ratio of HF:SnCl2, it is required tooptimize TMCS concentration. For this purpose, several substrateswere prepared by dipping in solution HF:SnCl2 with a ratio of 10:1.Then, they were immersed in TMCS ethanol solution with variedconcentrations for 24 h. The results are demonstrated in Fig. 3.

Based on Fig. 3, without TMCS modification, the WCA is nearly zero.In this situation, there is no addition of TMCS and only FTO depositionexisted on the glass substrate. It shows that FTO glass is superhydrophilicand after the dropping ofwater on the FTO glass, a complete spreading ofwater occurred. Furthermore, the WCA climbed by increasing the TMCS



Fig. 1. WCA on glass substrate. a) without and b) with TMCS modification.

3T. Rezayi, M.H. Entezari / Surface & Coatings Technology xxx (2015) xxx–xxx

concentration. At a low concentration of TMCS, there is no sufficientmodifier to cover the glass substrate completely. But, at concentrationequals to 10% v/v, WCA went up considerably (156.58° ± 1.51°) andSHS were achieved. Beside high WCA in this concentration, the SA was25.33° ± 2.02°. Addition of TMCS concentration to 16% v/v does nothave a noticeable affect on the WCA and SA. At this concentration,WCA and SA were 156° ± 3.21° and 26.33° ± 2.33°, respectively. It isimportant to note that the SA was about 90° for the glass substratesresulting from TMCS immersion with concentration lower that 10%.

Another parameter that can be optimized is the timeof immersion inTMCS (10% v/v). The results of this investigation have been plotted inFig. 4.

It can be clearly seen from Fig. 4 that immersion in TMCS (10% v/v)for 4 h reached to the highest WCA and after that it was maintained atthe same level. In addition, according to SA results, SA gets a minimumvalue at 8 h of immersion time. Further immersion has a negligibleeffect on the SA.

3.3. Structural analysis of deposited films on glass substrate

3.3.1. SEM and AFM investigationsFig. 5 demonstrates the SEM and AFM images of bare, FTO deposited

and SH glass under the optimum conditions. It can be pointed out thatthe bare glass has a smooth surface. However, after deposition of FTOon the glass, the smoothness converts to enhanced roughness, whichis essential to create SHS. Fig. 5b shows the existence of regular anddense nanostructure roughness. There are numerous voids and crackson this surface that improve the surface unevenness. The sizes of depos-ited particles are in the range of 200–400 nm. The created roughness ac-companywith TMCS as surface energy reduction agents are responsiblefor WCA increase on the glass. After TMCS modification (Fig. 5c), theuniformity of the surface has been improved and smaller particleshave been created (100–200 nm). Consequently, the transparency hasbeen dramatically increased after TMCS modification (Fig. 8). In some

Fig. 2. The WCA versus HF:SnCl2 ratio. All samples were immersed in TMCS ethanolsolution (10% v/v) for 24 h.


points, the agglomeration of nanoparticles led to empty spaces, whichare suitable areas for air trapping and increasing of WCA values.

For more accurate assessment, AFM images are presented accompa-nied with SEM ones (Fig. 5d–f). Besides, the results of quantitative mea-surements of surface roughness, such asmean roughness (Ra), rootmeansquare roughness (Rms) andmean roughness depth (Rz) are summarizedin Table 1.

It is clear that the roughness parameters change after FTOdepositionas well as after TMCS modification. The Rms parameter, which is morecommon for roughness evolution, increases from 0.370 ± 0.095 nm to2.360 ± 0.780 nm after FTO deposition. Therefore, it can be a sign ofroughness improvement in FTO deposition.

Apart from roughness parameter measurement, AFM analysis is ahelpful technique for estimation of film thickness. Assessment of heighthistogram has been regarded for this purpose. The thickness measuredusing this method is devoted to an area of 5 μm × 5 μm. Based on thisway the thickness of the deposited film was roughly 7 nm.

3.3.2. FTIR analysisThe FTIR analysis is very useful in the prediction of surface

structure. Fig. 6 represents the FTIR spectra of bare glass in comparisonwith FTO deposited glass. It must be noted that for the bare glass, thepeaks that appear at 1249 cm−1 and 880 cm−1 are assigned to Si–Ostretching and Si–OH bond, respectively [25]. Broad peak at 760 cm−1

is allocated to Si–O vibration and the peak at 469 cm−1 is for Si–O–Sibending mode [26,27]. Characteristic peaks of bare glass are observedin FTO glass substrate too. However, a distinguishable differencebetween two spectra comes into sight at 447 cm−1 and 487 cm−1.These peaks are related to Sn–O and Sn–F vibration bond (α − SnF2)correspondingly [15,28]. Also, a very weak peak can be found at~620 cm−1 after FTO deposition on glass substrate which can beassigned to Sn–O stretching vibration [29]. In deposited film, the fluo-rine ions (F−) are replaced with oxygen ions (O−2). The replacementcan be attributed to the nearly equal ionic size (F−:0.133 nm and

Fig. 3. The WCA versus TMCS concentration. All samples were prepared by dipping insolution HF:SnCl2 with 10:1 ratio.



Fig. 4.WCA and SA versus time immersion in TMCS solution.

Fig. 5. SEM (a–c) and AFM (d–f) images of bare glass

Table 1Roughness parameter for bare glass, FTO deposited glass (HF:SnCl2 with 10:1 ratio) andSH glass.

Roughnessparameter (nm)

Bare glass FTO deposited glass SH glass

Ra 0.089 ± 0.024 0.295 ± 0.097 0.170 ± 0.05Rms 0.370 ± 0.095 2.360 ± 0.780 1.210 ± 0.350Rz 0.890 ± 0.274 2.350 ± 0.094 1.970 ± 0.600



O−2:0.132 nm), and comparability of their bond energy with Sn (Sn–Fbond ~26.75 D°/kJ mol−1 and Sn–O bond 31.05 D°/kJ mol−1). TheCoulomb forces that bind the lattice together are reduced because thecharge on the F− is half of the charge on O−2. Therefore, geometricallythe lattice is not capable to distinguish between F− and O−2 [28]. Thissubstitution is well proved by the characteristic peak of Sn–F at487 cm−1 in FTIR.

Fig. 7 shows the FTIR spectra of FTO glass before and after TMCSmodification. For a more exact observation, the FTIR spectrum hasbeen enlarged in a lower wave number range and shown inside Fig. 7.An extreme increase in the peak intensity located at 447 cm−1 can beseen after TMCS modification. Besides, a remarkable decrease in thepeak intensity at 487 cm−1 has been observed after TMCSmodification.It should be ingeminated that the peak at 447 cm−1 is Sn–O representa-tive peak and the peak at 487 cm−1 is characteristic peak of ∝ − SnF2.These differences are very important for the prediction of themechanism.

, FTO deposited glass and SH glass respectively.



Fig. 6. FT-IR spectra of the a) bare and b) FTO deposited glass substrates.

Table 2EDX results of bare and FTO glass substrates. The numbers are in term of atomic ratio (%).Sample was prepared by dipping in solution HF:SnCl2 with 10:1 ratio.

Element Si O Sn F

Bare glass 33.33 66.66 – –FTO glass 31.83 65.77 1.82 0.57


It seems that new Sn–O band has been created after TMCS modification,whichwill resulted in an increase in Sn–Opeak intensity. The exact obser-vation of FTIR spectra after TMCS modification can be resulted in a newpeak at 1065 cm−1. This peak is assigned to C–O stretching vibrationand it is an evidence for the presence of TMCS on the surface [30]. Besides,another peak that appeared after TMCS modification at 590 cm−1 is acharacteristic peak of the Si–O bond vibration. The presence of this peakcan be arising from a modifier that contained Si element [31].

3.3.3. EDX analysisAccording to the EDX data in Table 2, only Si and O elements are

available in the bare glass. Besides, the presence of Sn and F elementshas been demonstrated for FTO films. The EDX technique is helpful fordetermining final F content in the deposited film. Based on these data,it can be concluded that the F/Sn atomic ratio within the film is lessthan that was taken in the initial solution. The presence of Sn–Oand Sn–F bonds in FTO film has been verified previously with FTIRtechniques and it is in compatibility with EDX results (Table 2).

Overall, SEM, AFM, FTIR, and EDS techniques are able to demonstratethe presence of deposited film on the glass. However, XRD assessmentdoes not lead to any characteristic peak. In other word, the structureof FTO film is weakly crystallized.

Fig. 7. FT-IR spectra of FTO glass before and after TMCS modification.


3.4. Optical properties

Fig. 8 compares the optical transmission of bare glass with FTO andSH glass substrates. As it is shown, the SH glass substrate has a hightransparency especially in visible regions and there is an extremesimilarity between bare glass and SH glass spectra except at a lowwave-lengthwhich is related to the absorption of deposited layer. Additionally,the FTO glass has a broad peak falling to the lowest point at awavelengthequal to 305 nm. After TMCSmodification of the FTO glass substrate, thebroad peak of the FTO glass changes to a narrow one that is a sign oftransparency enhancement. Furthermore, in Fig. 9, the images of waterdroplets on the deposited layer of glass substrate are presented. As canbe seen, the letters underneath the superhydrophobic glass are observedclearly. Therefore, the SH glass substrate which has been synthesized inthis work possesses a remarkable transparency.

3.5. Thermal stability

The thermal stability of SHS on glass substrateswas carried out by an-nealing the samples at different temperatures ranging from 353 K to673 K. The results of this investigation have been shown in Fig. 10.Based on this figure, the high WCA can be kept until 473 K (141.15° ±3.08°). At higher temperatures the deposited TMCS has been removedfrom the surface and leads to a decrease of WCA.

3.6. Stability against the pH of medium

For more investigations on the modified glass substrate, the resis-tance of the surface has been evaluated against water droplet with pHranging from 1 to 14. The results of this investigation are presented inFig. 11. It is clear that there is no remarkable change in WCA when thepH of water droplet varied between 1 and 9. Therefore, the depositedlayer on the glass surface is stable against acidic droplet. Whereas, atpH higher than 9, a considerable decline in WCA can be seen. It meansthat the durability of the surface in contact with basic droplets is low.

Fig. 8. Optical transmission of bare glass and superhydrophobic glass substrates.



Fig. 9. The optical photograph of water droplet on superhydrophobic glass substrate.

Fig. 11. WCA and SA versus various pH domains of water droplet on superhydrophobic


In addition, based on Fig. 11, the SA is low in the pH range of 1–9 andover this range the SA is dramatically increased.

It is worthy to note that, the images were captured in 10 s afterdropping. The instability of SH surface against basic droplet can beassigned to the presence of electronegative elements such as F and Oon this surface (reaction 3). These elements give a partial positivecharge to hydrogen atoms. Therefore, in contact with basic droplets,hydroxyl ions can interact with this partially positive hydrogen.Consequently, WCA will be decreased and SA will be increased in thissituation.

3.7. Proposed mechanism

The importance of HF addition for the creation of superhydrophobicproperty is reflected in WCA results. According to Fig. 2, without HFaddition, it is not possible to reach high WCA values. Therefore, thereaction mechanism was examined in the absence and presence of HF.

Based on the Experimental section,withoutHF addition, SnCl2 and IPAare present in the reaction container. The pH values before (pH = 5.72)and after SnCl2 dispersion in IPA (pH= 1.45) can verify the HCl creationin this process (reaction 1).

ð1Þ

Besides, UV–vis spectra of SnCl2 in IPA before and after refluxing canbe used for the represent of valence number change of tin. From Fig. 12,

Fig. 10. The WCA versus annealing temperature for superhydrophobic glass substrate.


it is obvious that before refluxing there are two peaks around 214 and221 nm and after refluxing at 70 °C for 1 h, the peaks disappeared.This transform is a reason of valance change of tin. The vanishing ofthese peaks after refluxing can confirm the creation of tetravalent tin[24]. Therefore, Scheme 1 shows the mechanism proposed for the crea-tion of SnO2 on glass substrate in the absence of HF.

Therefore, in the absence of HF, it is expected to have SnO2 deposi-tion on the glass substrate. The WCA results showed that after immer-sion of this surface in TMCS ethanol solution, a dramatic increase in

glass substrate.

Fig. 12. UV–vis spectra of SnCl2 in IPA before and after refluxing.



Scheme 1. Suggested mechanism for the creation of SnO2 in IPA without HF addition.


WCA value was not observed. In TMCS ethanol solution, the followingreaction (2) can take place:

ð2Þ

The oxygen in trialkylsilyl derivative acts as a Lewis base, but SnO2 isan amphoteric oxide and has no sufficient acidic activity in contact withoxygen. Consequently, there is no strong bonding between SnO2 depos-ited on glass substrate and oxygen in trialkylsilyl. However, after HFaddition, based on FTIR results, O−2 can be replaced with F−. Becauseof stronger electronegavity property of F− in comparison with O−2,the resulted SnF2 has a remarkable acidic activity and acts as Lewisacid in contact with trialkylsilyl. As a result, a dative bonding betweenthese Lewis acid and base is created and confirms the observed highWCA after HF addition. The probable chemical reaction (3) may beexplained as follows.

ð3Þ

4. Conclusions

In summary, a highly transparent superhydrophobic glass substratehas been synthesized using a simple sol–gel dip coating technique. TheFTO deposition accompanied by TMCS modification have been used tocreate appropriate roughness and surface energy reduction, respective-ly. The highest WCA (156.58° ± 1.51°) and the lowest SA (25.33° ±2.02°) result when the HF:SnCl2 ratio equals 10:1 in the startingsolution. Besides, TMCS ethanol solution concentration and the time ofimmersion in this solution are important factors, which affected theWCA values. The SHS of the glass substrate showed a high resistanceagainst acidic droplets. Also, annealing of the glass up to 473 K, presenteda WCA equal to 141.15° ± 3.08°. The method employed in this workis facile and economical; therefore, it is expected to find a widespreadapplication in areas such as self-cleaning glass fields.


Acknowledgments

The support of Ferdowsi University of Mashhad (Researchand Technology) for this work (code 3/29793, date 28/01/2014)is appreciated.

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