Article pubs.acs.org/JPCC
Hydrogen Bonding Effect on Wettability of Polysiloxane Coatings Jie Zha, Xin Lu, and Zhong Xin* State Key Laboratory of Chemical Engineering, School of Chemical Engineering, East China University of Science and Technology, P.O. Box 545, Meilong Road 130, Shanghai 200237, People’s Republic of China ABSTRACT: The effect of thermal treatment on surface wettability of polysiloxane coatings was fully studied. In contrary to the enhanced hydrophobicity of methyltrimethoxysilane (MTMS)-based coatings, the water contact angle of tetraethoxysilane (TEOS)-based coatings decreased from 70.8 to 52.8° when temperature increased from 100 to 300 °C. It was confirmed by FT-IR, solid state 29Si NMR, and X-ray photoelectron spectroscopy measurements that compared with MTMS-based coatings, that TEOS-based coatings consisted of more silanol groups, most of which were in the form of intramolecular hydrogen bonds. The further condensation at higher temperature led to a rupture of these intramolecular hydrogen bonds, resulting in high surface free energy and thus hydrophilic surface. Besides, this hydrogen bonding effect on wettability was weakened as the content of MTMS went up in MTMS/TEOS hybrid coatings.
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INTRODUCTION In the past decade, silica-based nanostructured coatings have been one of the well-developed areas of nanotechnology for their wide applications as antimicrobial, antifingerprinting, selfcleaning, antiscratch, antifogging, antiadhesive, and anticorrosion coatings.1,2 Among the industrial-viable approaches to produce these coatings, sol−gel chemistry is one of the most prominent because of its versatility, low cost, mild condition in liquid phase, and ease to combine with simple deposition techniques (spraying, dip- or spin-coating, etc.).3−5 Wettability is one of the fundamental property of coatings, which has aroused much interest due to the great advantages of functional surfaces with special wettability.6 For instance, “lotus-effect”-based superhydrophobic surfaces have been widely used in self-cleaning and anti-icing conditions,7−9 while surfaces with superhydrophilicity are potential for water-collecting, antifogging, and so forth.7,10 Since sol−gel process is versatile, the surface wettability of coatings can be widely tailored by changing precursors, reaction condition, or applying various post-treatments. Through incorporating TiO2 as outer layer, the composite coatings revealed better selfcleaning property.11 The hydrophobicity of silica coatings could be enhanced by co-condensation with alkyl-functionalized silane.10 Classical sol−gel method generally involves thermal treatments at temperatures to prompt condensation reaction. In a recent study on sol−gel based hydrophobic antireflective coatings, the methyl modified silica network revealed its hydrophobicity with thermal treatment at 350 °C, which followed a rearrangement mechanism that the methyl groups relocated from inside the oxide network toward the surface of the oxide pores at high temperature.12 Except from this interesting finding, however, the effect of thermal treatment on wettability of polysiloxane coatings has not been fully explored © 2014 American Chemical Society
and further investigations are still required to effectively adapt the wettability of sol−gel coatings to their functioning environment. Therefore, in this present work the surface wettability of polysiloxane coatings was carefully studied through a comprehensive investigation with assistance of FTIR, solid-state 29Si NMR, X-ray photoelectron spectroscopy, contact angle measurement, and so forth.
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EXPERIMENT Materials. Methyltrimethoxysilane (MTMS) provided by Danyang Organic Silicon Industry Co., Ltd. was purified by collecting fraction under vacuum distillation prior to use. Tetraethoxysilane (TEOS), absolute ethanol, and hydrochloric acid (HCl) were from Shanghai Lingfeng Chemical Corp., which were all used as received. All the solutions were prepared with Milli-Q (18.2 MΩ·cm, 25 °C) water. Sol Preparation. Polysiloxane films were prepared from solutions composed of MTMS, TEOS, ethanol, HCl, and H2O with molar ratio of x/y/50/0.005/5. In this present work, the molar ratio of MTMS to TEOS was set to 10:0, 7:3, 5:5, 3:7, and 0:10. In a typical experiment, MTMS and TEOS were first dissolved in ethanol and adequate water. Then HCl was added dropwise to adjust the pH to around 2.0 for hydrolysis of precursors. After 2 h of hydrolysis, the sol solutions were diluted with ethanol and aged for sequent dip-coating. A schematic illustration of sol preparation was displayed in Scheme 1a. Dip-Coating Process. Prior to coating, all glass slides were ultrasonically cleaned with detergent and ethanol, rinsed with water, and then dried. The dip-coating process was illustrated in Received: October 3, 2014 Revised: November 24, 2014 Published: December 16, 2014 420
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solid-state accessory. Spectra were recorded using a highresolution magic-angle spinning assembly at spinning speed of ∼5 kHz. The 90° pulse length for the nuclei 29Si was ∼2.9 μs. Tn and Qn were used to represent trifunctional and tetrafunctional silica species, respectively. The X-ray photoelectron spectroscopy (XPS) experiments were carried out on a Thermo Fisher ESCALAB 250Xi photoelectron spectrometer employing a monochromated Al Kα X-ray source. Survey spectra were captured using a pass energy of 100 eV, and scan spectra were captured at 20 eV, with energy step size of 0.05 eV. The XPS spectra of 10M and 5M coatings were charge corrected to position C 1s (CH3−Si) at 284.5 eV, and spectra of 0M coatings were corrected to position C 1s (CH3−CH2−) at 285.0 eV.13−15 The surface roughness (Ra) was verified by atomic force microscope (AFM) using a Digital Instruments multimode scanning probe microscope (NanoScope IIIa) in an area of 2.0 × 2.0 μm2. AFM was employed in the tapping mode by using silicon nitride cantilevers. The contact angle (CA) measurement was performed using a Dataphysics OCA 20 optical goniometer to qualify the surface wettability of resultant coatings. Water droplets of 2 μL volume were used with ellipse fitting for contact angle measurements. Surface free energy was evaluated using Van Oss and Good’s three-liquid method.16 Typically, the surface free energy of all samples were calculated by eqs 1 and 2 as follows
Scheme 1. Schematic Illustration of (a) Sol Preparation and (b) Dip-Coating Process of Polysiloxane Coatings on Glass Substrate (Double-Side Coated)
Scheme 1b. Glass slides were vertically immersed into sol solutions and withdrew at a rate of 100 mm/min. Afterward, the double-side coated glass substrates were heated in three sequent steps as follows: at 100 and 200 °C, each for 30 min, and finally at 300 °C for 10 min. The resultant films were named in terms of the content of MTMS in coating solutions. For instance, 10M represented the film obtained from sol solution with MTMS/TEOS molar ratio of 10:0. Characterization Methods. Fourier transform infrared spectroscopy (FT-IR) measurements were carried out on a FTIR spectrometer to study qualitatively the extent of silica polymerization at room temperature (25 °C) using the KBr pellet method. The samples were prepared by casting sol solution directly onto a KBr plate and then calcinated at certain temperature. All the spectra were recorded in absorption with system settings of 32 scans and a resolution of 4 cm−1. The films condensation process was also examined through solidstate 29Si NMR measurement on a Bruker Avance 500 MHz spectrometer (silicon frequency 99.36 MHz) with a Bruker
γL(1 + cos θ ) = 2( γSLWγLLW + γS = γSLW + 2 γS+γS−
γS+γL+ +
γS−γL− )
(1) (2)
+ − where γL is the surface tension of test liquid, and γLW L , γL, and γL are, respectively, the Lifshitz−van der Waals, Lewis acid, and Lewis base components of γL. Similarly, γS is the surface free + − energy of solid film, and γLW S , γS and γS are Lifshitz−van der Waals, Lewis acid, and Lewis base components of γS,
Figure 1. (a) The FT-IR spectra of 10M and 0M films at 300 °C and the spectra of (b) 0M, (c) 3M, (d) 5M, (e) 7M, and (f) 10M films at various temperatures. 421
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respectively. θ is the measured contact angle. We measured the contact angles of deionized water, ethylene glycol (EG), and diiodomethane (DIM) (99%) to determine the surface free energy. To obtain reliable contact angle data, five droplets were dispensed at different regions of the films.
Scheme 2. Possible Associate Hydroxyl in Polysiloxane Films: (a) Intermolecular Hydrogen Bonds and (b) Intramolecular Hydrogen Bonds
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RESULTS AND DISCUSSION Chemical Component of Polysiloxane Coatings. Polysiloxane coatings were obtained through a sol−gel dipcoating method. First, acid-catalyzed hydrolysis of silane precursor and then dip-coating followed by heat-induced condensation. Figure 1a showed respectively the FT-IR spectra of 10M and 0M films heated at 300 °C. The characteristic band of silica network was found around 1000−1200 cm−1 for Si− O−Si asymmetric vibration. As seen in the spectrum of 10M film, a Si−C stretching vibration at 775 cm−1, a −CH3 symmetric and asymmetric deformation vibration respectively at 1275 and 1408 cm−1 corresponded to the Si-CH3. Also, an symmetric and asymmetric stretching vibration of CH3 at 2910 and 2975 cm−1 (Figure 1f) confirmed the presence of Si-CH3, while the two tiny peaks around 2910 and 2975 cm−1 detected in the spectra of 0M film (Figure 1b) could be attributed to the symmetric and asymmetric stretching vibration of −CH3 and −CH2− of the unhydrolyzed ethyoxyl groups in TEOS-based films. The temperature effect on polysiloxane films was investigated by analyzing FT-IR spectrum of 10M and 0M films at different temperature. As shown in Figure 1b,f, the absorption around 3610 cm−1 in both spectra of 0M and 10M films corresponded to free hydroxyl,17 which could be assigned to the unreacted Si−OH and adsorbed water. As temperature increased, the intensity of free −OH gradually decreased due to the further condensation of silanol and the removal of absorbed water and almost disappeared in the curve of 10M film at 300 °C but still obviously remained in the curve of 0M film. Because adsorbed water could be fully eliminated at this high temperature, the remaining Si−OH should be solely amenable for the existence of free −OH at 300 °C. Moreover, the broad absorption band 3000−3600 cm−1 could be attributed to the associate hydroxyl. Noll et al.18,19 has proved that it was nearly impossible to form hydrogen bonds between hydroxyl directly bonded to silicon atom and oxygen atom within polysiloxane. According to the study on hydrogen bonding by Chang,20 the associate hydroxyl in polysiloxane films could be classified into the association between silanols, the hydrogen-bonded adsorbed water molecules, and the association between adsorbed water and silanol. The former interaction (around 3200 cm−1) was intramolecular hydrogen bonding, while the latter two (around 3450 cm−1) was intermolecular hydrogen bonding, as shown in Scheme 2. To provide a further analysis of these associate hydroxyl the spectra were deconvoluted into Gauss curves (Figure 1b−f). Because it was the first time to present a detailed insight into hydrogen bonding in polysiloxane materials, some interpretations of deconvolution might suffer from errors due to the curve-fitting procedure. As a whole, all the curve-fits possessed a R-squared above 0.9 and thus were reliable to a great extent. For TEOS-based silica films, it was found that the association between silanols (∼3200 cm−1), that is, intramolecular hydrogen bonds, dominated the associate hydroxyl and the intensity of this absorption was still considerable at 300 °C. The case, however, was different for MTMS-based polysiloxane films, where intermolecular hydrogen bonds (∼3450 cm−1) played a major role and the
absorption of the associate hydroxyl almost disappeared at 300 °C. The solid-state 29Si NMR measurement of 5M film was conducted to further investigate the temperature effect on the component of polysiloxane films. The spectra were deconvoluted into Gauss curves for ease of analysis. The peaks of chemical shifts at about −61 and −68 ppm, and −108 and −115 ppm (Figure 2) could be assigned to T2, T3, Q3, and Q4
Figure 2. Solid-state temperatures.
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Si NMR spectra of 5M film at different
species, respectively, where Tn represented (SiO)n(OH)3‑nSiCH3 groups from the hydrolysis and condensation of MTMS, and Qn represents Si(OSi)n(OH)4‑n groups from TEOS.21,22 The proportion of each characteristic peak was calculated based on the deconvolution results, which is listed in Table 1. The calculated ratio of T2/T3 and Q3/Q4 at 100 °C was respectively 0.75 and 3.13, indicating more Si−OH Table 1. Calculated Proportion of Each Characteristic Peak in Solid-State 29Si NMR Spectra of 5M Film at Different Temperatures thermal treatment
422
T2
T3
Q3
Q4
temperature (°C)
(%)
(%)
(%)
(%)
100 200 300
20.7 10.9 8.3
27.7 36.2 38.3
39.2 36.8 37.0
12.5 15.2 15.4
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Figure 3. Curve-fits of 0M, 5M, and 10M coatings at 300 °C temperature for (a) C 1s core level and (b) O 1s core level.
groups in TEOS-based silica films. As temperature increased to 300 °C, about 12% of T2 species transformed into T3 species, while only 2.5% of Q3 species changed into Q4 species. The results indicated the difficulty in condensation of tetraalkoxysilane, which agreed with the FT-IR results that both free and associate hydroxyl still existed in TEOS-based films even after heating at 300 °C but the absorption related to hydroxyl could hardly be detected in MTMS-based films at 300 °C. It could be concluded from the results of FT-IR and NMR measurements that the intramolecular hydrogen bonded Si−OH dominated the associate hydroxyl in TEOS-based film due to the high proportion of uncondensed silanols, while played a minor role in MTMS-based film because of the relatively few silanols from easily condensed organotrialkoxysilane. The detailed analysis of FT-IR and solid-state NMR 29Si has been presented to identify the chemical compositions of bulk materials at different temperatures. Furthermore, XPS, a surface-sensitive technique, was employed to verify the chemical compositions at surfaces. Figure 3 shows the curvefits of C 1s and O 1s core level for 0M, 5M, and 10M coatings at 300 °C. All the curves were organized at the same scale as in their survey spectra. The curve-fitting was conducted mostly according to previously published results. For some cases where the characteristic peaks have not been reported, we performed the curve-fitting based on our best knowledge. The C 1s peaks in 0M coatings (Figure 3a) was due to the presence of unhydrolyzed ethyoxyl groups of TEOS as previously confirmed by FT-IR. Because the carbon atom of methylene in ethyoxyl was simultaneously bonded to a oxygen atom and another carbon atom, it should have a higher binding energy (BE) than the carbon atom of methyl. Hence, the curve of 0M was divided into two portions with BE of 285.0 ± 0.1 and 285.6 ± 0.1 eV for methyl and methylene, respectively. With the addition of MTMS, the peaks at BE of 284.5 ± 0.1 eV, corresponding to methyl group bonded to silicon atoms,15 were detected in 5M and 10M coatings, and the curve of 10M coatings revealed a higher intensity at this position. Because of the unhydrolyzed methoxyl groups of MTMS, a tiny peak at BE of 285.4 ± 0.1 eV was applied, representative of carbon atoms of methoxyl groups. The molar ratio of carbon to silicon (C/Si) was calculated as 0.57, 0.72, and 1.24, respectively, for 0M, 5M, and 10M coatings, indicating more carbon atoms at coatings surface with increased content of MTMS. Figure 3a illustrated the curve-fits of O 1s core level. According to the XPS study on
siloxane materials by O’Hare et al.,14,15 oxygen atoms within Si−O−Si network revealed different BE value, 532.8 ± 0.1 and 532.3 ± 0.1 eV, respectively, for Q and T species. This may explain the shift of peaks corresponding to O in Si−O−Si toward lower BE value when the content of MTMS is higher. The position of hydroxyl varied in references,23 and the position at BE of 531.8 ± 0.1 eV was used in our analysis. The calculated molar ratio of hydroxyl to silicon (−OH/Si) were, respectively, 0.24, 0.18, and 0.08 for 0M, 5M, and 10M coatings, an indicative of higher content of hydroxyl in TEOSbased coatings. Moreover, the −OH/Si of 5M coatings at 100 and 200 °C were 0.34 and 0.24, respectively, greater than that at 300 °C, which can be attributed to the further condensation at higher temperature. The results of chemical compositions at coatings surface were in good agreement with the analysis of bulk materials by FT-IR and solid-state 29Si NMR. Surface Wettability. Generally, alkyl-functionalized silica precursor can enhance the hydrophobicity of Si−O−Si network.10,24 In this present work, the effect of temperature on the wettability of polysiloxane coatings, consisting of various MTMS/TEOS molar ratios, was further investigated. Figure 4
Figure 4. Water contact angles of films with various MTMS/TEOS molar ratios at different temperatures.
showed the water contact angle of MTMS/TEOS coatings at different temperatures. The error bars were omitted here because the calculated standard deviation of each testing point was rather minimal of approximately 0.1−0.3 (o). It was obvious that 0M film was the most hydrophilic with CA of 52.8° at 300 °C, while 10M film showed the highest 423
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increase the surface free energy, resulting in a more hydrophilic surface. For MTMS/TEOS hybrid films, however, the effect of intramolecular hydrogen bonding on surface energy gradually weakened with the increase of MTMS in precursors. Furthermore, we calculated the surface free energy of films with various MTMS/TEOS molar ratios at different temperatures, as shown in Figure 5. Because hydrogen-bonding
hydrophobicity with CA of 96.1° due to the presence of abundant hydrophobic methyl groups in MTMS based film, which was verified by the XPS results. In addition, films with various MTMS/TEOS molar ratio behaved differently as temperature increased. For 10M, 7M, and 5M films, they became more hydrophobic with temperature increasing from 100 to 300 °C, which could be attributed to the elimination of hydrophilic −OH groups in further condensation. In a recent work by Boudot et al.,12 they presented a rearrangement mechanism that the methyl groups relocated from inside the oxide network toward the surface of the oxide pores at high temperature, which enriched the interfaces with hydrophobic groups. This mechanism could also explain the increased hydrophobicity of 10M, 7M, and 5M films. However, cases were different for 3M and 0M films. The CA of 3M film revealed a slight decrease when heated at 300 °C, while a significant drop in CA was detected for 0M film from 70.8° down to 52.8°. Hence, the rearrangement mechanism was not appropriate for the weakened hydrophobicity of 3M and 0M films. Neither could the decease of hydrophilic groups at high temperature be solely responsible for enhanced hydrophobicity, because it was believed that the amount of −OH in 3M and 0M films would also decrease due to the further condensation reaction at high temperature. As is well-known, both the surface topographic structure and the chemical compositions have a great influence on wettability.6,25,26 Table 2 listed the roughness (Ra) of 10M,
Figure 5. Calculated surface free energy of films with various MTMS/ TEOS molar ratio at different temperatures.
Table 2. Roughness of 10M, 5M, and 0M Films Treated at Different Temperatures
interaction is considered in Van Oss and Good’s three-liquid method,16 it was used in the calculation of surface free energy in our experiment. The calculation results well agreed with the above proposed hydrogen bonding effect on the surface free energy at various temperatures.
Ra(nm) film samples
100 °C
200 °C
300 °C
10M 7M 5M 3M 0M
0.312 0.297 0.395 0.363 0.291
0.354 0.306 0.427 0.344 0.273
0.422 0.321 0.476 0.307 0.252
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CONCLUSION In this paper, MTMS/TEOS-based coatings were prepared through a sol−gel dip-coating method and the thermal treatment effect on coatings wettability was carefully studied. In contrary to the enhanced hydrophobicity of MTMS-based coating, the water contact angle of TEOS-based coating decreased from 70.8 to 52.8° when temperature increased from 100 to 300 °C. It was confirmed by FT-IR, solid state 29Si NMR, and XPS measurements that different from MTMSbased coating, TEOS-based coating consisted of more silanol groups most of which formed intramolecular hydrogen bonds within silica network. We proposed that the condensation between intramolecular hydrogen bonded silanols at high temperature may lead to a rupture of intramolecular hydrogen bonding, resulting in high surface free energy and thus hydrophilic surface. Moreover, it was found that this hydrogen bonding effect on wettability was weakened in high MTMS/ TEOS molar ratio. With a further understanding of the relationship between thermal treatment and wettability of polysiloxane coatings, it would be more effective to adapt these coatings to their functioning environment.
7M, 5M, 3M, and 0M films at various temperatures. All the samples showed extremely smooth surface. It was also found that the roughness of tested films changed little when temperature increased, which would not significantly affect the final wettability. Therefore, a deep insight into the chemical component of resultant films would benefit our understanding of the different wettability of polysiloxane films at various temperatures. As previously discussed, the results of FT-IR, NMR, and XPS measurements proved that MTMS- and TEOSbased films differed widely in the associate hydroxyl. Compared with MTMS-based films, TEOS-based films possessed more associate hydroxyl in which intramolecular hydrogen-bonded hydroxyl dominated. According to the hydrogen-bonding study in publications20,27,28 and our group,29,30 the formation of intramolecular hydrogen bonding could reduce the surface free energy, leading to high hydrophobicity. Hence, we proposed a plausible mechanism for the alteration of wettability as follows. The further condensation reaction at high temperature reduced the amount of silanol, leading to the decrease of intramolecular hydrogen bonding between Si−OH. Because of the large amount of hydroxyl in TEOS-based films, hydrogen bonds, especially the intramolecular bonded, played an important role in their surface free energy. Hence, as temperature went up, the decrease of intramolecular hydrogen bonds could greatly
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AUTHOR INFORMATION
Corresponding Author
*E-mail:
[email protected]. Tel.: +86-21-64252972. Fax: +8621-64240862. Notes
The authors declare no competing financial interest. 424
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(20) Wang, C. F.; Su, Y. C.; Kuo, S. W.; Huang, C. F.; Sheen, Y. C.; Chang, F. C. Low-Surface-Free-Energy Materials Based on Polybenzoxazines. Angew. Chem., Int. Ed. 2006, 45 (14), 2248−2251. (21) Lu, X.; Yin, Q. F.; Xin, Z.; Zhang, Z. Q. Powerful Adsorption of Silver(I) onto Thiol-functionalized Polysilsesquioxane Microspheres. Chem. Eng. Sci. 2010, 65 (24), 6471−6477. (22) Yang, X. L.; Zhao, N.; Zhou, Q. Z.; Wang, Z.; Duan, C. T.; Cai, C.; Zhang, X. L.; Xu, J. Facile Preparation of Hollow Aminofunctionalized Organosilica Microspheres by a Template-free Method. J. Mater. Chem. 2012, 22 (34), 18010−18017. (23) Erdem, B.; Hunsicker, R. A.; Simmons, G. W.; Sudol, E. D.; Dimonie, V. L.; El-Aasser, M. S. XPS and FTIR Surface Characterization of TiO2 Particles Used in Polymer Encapsulation. Langmuir 2001, 17 (9), 2664−2669. (24) Krzyzak, M.; Frischat, G. H.; Hellmold, P. Surface Finishing of Enamels by Sol-Gel Coating. J. Sol-Gel. Sci. Technol. 2007, 41 (1), 99− 102. (25) Woodward, J.; Gwin, H.; Schwartz, D. Contact Angles on Surfaces with Mesoscopic Chemical Heterogeneity. Langmuir 2000, 16 (6), 2957−2961. (26) Sun, T.; Song, W.; Jiang, L. Control over the Responsive Wettability of Poly (N-isopropylacrylamide) Film in A Large Extent by Introducing An Irresponsive Molecule. Chem. Commun. 2005, 13, 1723−1725. (27) Lin, S.-Y.; Chen, K.-S.; Liang, R.-C. Thermal Micro ATR/FT-IR Spectroscopic System for Quantitative Study of the Molecular Structure of Poly (N-isopropylacrylamide) in Water. Polymer 1999, 40 (10), 2619−2624. (28) Chino, K.; Ashiura, M. Themoreversible Cross-linking Rubber Using Supramolecular Hydrogen-bonding Networks. Macromolecules 2001, 34 (26), 9201−9204. (29) Qu, L.; Xin, Z. Preparation and Surface Properties of Novel Low Surface Free Energy Fluorinated Silane-Functional Polybenzoxazine Films. Langmuir 2011, 27 (13), 8365−8370. (30) Liu, J.; Lu, X.; Xin, Z.; Zhou, C. Synthesis and Surface properties of Low Surface Free Energy Silane-functional Polybenzoxazine Films. Langmuir 2012, 29 (1), 411−416.
ACKNOWLEDGMENTS This research was financially supported by the Nanotech Foundation of Science and Technology Commission of Shanghai Municipality (No. 0652nm001), the National Natural Science Foundation of China (No. 21006025), and the Fundamental Research Funds for the Central Universities.
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REFERENCES
(1) Pagliaro, M.; Ciriminna, R.; Palmisano, G. Silica-Based Hybrid Coatings. J. Mater. Chem. 2009, 19 (20), 3116−3126. (2) Ciriminna, R.; Fidalgo, A.; Pandarus, V.; Beland, F.; Ilharco, L. M.; Pagliaro, M. The Sol-Gel Route to Advanced Silica-Based Materials and Recent Applications. Chem. Rev. 2013, 113 (8), 6592−6620. (3) Sanchez, C.; Julian, B.; Belleville, P.; Popall, M. Applications of Hybrid Organic-Inorganic Nanocomposites. J. Mater. Chem. 2005, 15 (35−36), 3559−3592. (4) Grosso, D. How to Exploit the Full Potential of the Dip-Coating Process to Better Control Film Formation. J. Mater. Chem. 2011, 21 (43), 17033−17038. (5) Brinker, C.; Frye, G.; Hurd, A.; Ashley, C. Fundamentals of SolGel Dip Coating. Thin Solid Films 1991, 201 (1), 97−108. (6) Sun, T. L.; Feng, L.; Gao, X. F.; Jiang, L. Bioinspired Surfaces with Special Wettability. Acc. Chem. Res. 2005, 38 (8), 644−652. (7) Yao, X.; Song, Y. L.; Jiang, L. Applications of Bio-Inspired Special Wettable Surfaces. Adv. Mater. 2011, 23 (6), 719−734. (8) Carretero-Genevrier, A. n.; Boissiere, C. d.; Nicole, L.; Grosso, D. Distance Dependence of the Photocatalytic Efficiency of TiO2 Revealed by in Situ Ellipsometry. J. Am. Chem. Soc. 2012, 134 (26), 10761−10764. (9) Helsch, G.; Deubener, J. Compatibility of Antireflective Coatings on Glass for Solar Applications with Photocatalytic Properties. Sol. Energy 2012, 86 (3), 831−836. (10) Faustini, M.; Nicole, L.; Boissiere, C.; Innocenzi, P.; Sanchez, C.; Grosso, D. Hydrophobic, Antireflective, Self-Cleaning, and Antifogging Sol-Gel Coatings: An Example of Multifunctional Nanostructured Materials for Photovoltaic Cells. Chem. Mater. 2010, 22 (15), 4406−4413. (11) Prado, R.; Beobide, G.; Marcaide, A.; Goikoetxea, J.; Aranzabe, A. Development of Multifunctional Sol-Gel Coatings: Anti-reflection Coatings with Enhanced Self-cleaning Capacity. Sol. Energy Mater. Sol. C 2010, 94 (6), 1081−1088. (12) Boudot, M.; Gaud, V.; Louarn, M.; Selmane, M.; Grosso, D. SolGel Based Hydrophobic Antireflective Coatings on Organic Substrates: A Detailed Investigation of Ammonia Vapor Treatment (AVT). Chem. Mater. 2014, 26 (5), 1822−1833. (13) McCafferty, E.; Wightman, J. Determination of the Concentration of Surface Hydroxyl Groups on Metal Oxide Films by a Quantitative XPS Method. Surf. Interface Anal. 1998, 26 (8), 549−564. (14) O’Hare, L. A.; Parbhoo, B.; Leadley, S. R. Development of a Methodology for XPS Curve-fitting of the Si 2p Core Level of Siloxane Materials. Surf. Interface Anal. 2004, 36 (10), 1427−1434. (15) O’Hare, L. A.; Hynes, A.; Alexander, M. R. A Methodology for Curve-fitting of the XPS Si 2p Core Level from Thin Siloxane Coatings. Surf. Interface Anal. 2007, 39 (12−13), 926−936. (16) Owens, D. K.; Wendt, R. Interfacial Lifshitz-van der Waals and Polar Interactions in Macroscopic Systems. Chem. Rev. 1988, 88 (6), 927−941. (17) Shull, E. Estimation of Hydroxyl, Methyl, and Phenyl in Dimethyldiphenyl Silicone Resins by Infrared Spectrophotometry. Anal. Chem. 1960, 32 (12), 1627−1630. (18) Damm, K.; Noll, W. Determination of Silanol Groups in Organopolysiloxane and Their Behavior on Thermal condensation. Kolloid-Z. 1958, 158 (2), 97. (19) Noll, W.; Damm, K.; Krauss, W. Kondensation und Warmebestabdugkit von Siliconharzen. Angew. Chem., Int. Ed. 1959, 71 (1), 45. 425
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