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Hydrophobic antireflective coatings with ultralow refractive index synthesized by deposition of methylated hollow silica nanoparticles
Materials Letters 183 (2016) 374–377
Contents lists available at ScienceDirect
Materials Letters journal homepage: www.elsevier.com/locate/matlet
Hydrophobic antireflective coatings with ultralow refractive index synthesized by deposition of methylated hollow silica nanoparticles Chaoyou Tao a,b, Hongwei Yan a, Xiaodong Yuan a, Qiang Yin a, Jiayi Zhu a, Wei Ni a, Lianghong Yan a, Lin Zhang a,n a b
Research Center of Laser Fusion, China Academy of Engineering Physics, Mianyang 621900, China Graduate School of China Academy of Engineering Physics, Beijing 100088, China
art ic l e i nf o
a b s t r a c t
Article history: Received 6 February 2016 Received in revised form 30 June 2016 Accepted 10 July 2016 Available online 12 July 2016
A new type of antireflective (AR) coating materials with easily tailorable refractive index were successfully prepared by the sol-gel method based on the deposition of colloidal hollow silica nanoparticles (HSNs). HSNs were synthesized using tetraethylorthosilicate (TEOS) as the precursor, and then modified by methyltriethoxysilane (MTES). It is found that the refractive index (n) can be precisely tuned between 1.15 and 1.09 by changing the MTES content, in a range that is not accessible to dense inorganic materials. AR properties of the coatings on K9 glasses were demonstrated. Furthermore, AR coatings are intrinsically hydrophobic with the water contact angle (WCA) up to 122.5°. & 2016 Elsevier B.V. All rights reserved.
Keywords: Antireflective Sol-gel preparation Thin films Ultralow refractive index Hydrophobicity
1. Introduction Nanoporous materials have been extensively exploited for antireflective (AR) coatings [1–3], and distributed Bragg reflectors [4]. However, the realization of practical devices with excellent optical properties has been hindered by the lack of optical materials with very low refractive indices, especially which closely matches the refractive index of air. Therefore, developing novel materials with refractive indices lower than that of conventional optically transparent materials has attracted a great deal of attention. Materials with n¼ 1.07 [5] and even n¼1.03 [6] have been obtained via chemical etching. The approach based on the burning off additional templates has been demonstrated to be effective in obtaining nanoporous layers [7]. Recently, two silica nanorod array films for broadband AR coatings with refractive indices as low as 1.08 and 1.05 have been fabricated via oblique-angle deposition process [2,8]. However, these methods involved either hazardous solvents, or high calcination temperatures, or expensive machines, which is disadvantageous to large-scale applications. It is well known that the sol-gel process is the most appealing method for the preparation of nanoporous materials because of its low process temperature, low cost, the high purity of the resulting materials and the availability of substrates with complex shapes n
Corresponding author. E-mail address: [email protected] (L. Zhang).
[9]. Though the formation of silica materials with a very low refractive index (n ¼1.11) has achieved [10], multifunctional coating materials with tunable and lower refractive index (o1.10), and hydrophobicity are highly desirable. The present contribution describes a novel method for the synthesis of hydrophobic silica AR coatings with an ultralow and easily tunable refractive index by the dip-coating deposition of hollow silica nanoparticles (HSNs). The approach is illustrated in Scheme 1. The effect of the MTES content on the HSNs, film morphology, refractive index, and hydrophobicity are discussed.
2. Experimental Tetraethoxysilicate (TEOS, 98þ %) was obtained from Alfa Aesar. Poly(acrylic acid) (PAA, M.W. 3000), methyltriethoxysilane (MTES) were purchased from Aladdin Chemistry. HSNs were prepared by the modified Stöber method [11]. Then varied MTES were added into the HSNs sols. These hybrid sols were stirred at 30 °C for 2 h and aged for 7 days to allow MTES to react fully. The weight ratio of MTES and TEOS (MTES/TEOS) ranged from 0 to 0.9. Samples of sols, HSNs were denoted as “S-A”, “HA”, respectively, in which A means MTES/TEOS. The sols were deposited on well-cleaned K9 glasses or silicon using the dip-coating process at a fixed withdrawal rate (1000 mm min 1). Samples of coatings were denoted as “F-A”. The morphologies of the HSNs were observed by transmission
http://dx.doi.org/10.1016/j.matlet.2016.07.042 0167-577X/& 2016 Elsevier B.V. All rights reserved.
Please cite this article as: C. Tao, et al., Hydrophobic antireflective coatings with ultralow refractive index synthesized by deposition of methylated hollow silica nanoparticles, Mater Lett (2016), http://dx.doi.org/10.1016/j.matlet.2016.07.042i
C. Tao et al. / Materials Letters 183 (2016) 374–377
375
Scheme 1. Schematic description of the developed synthesis method for hydrophobic HSNs films with tunable refractive index.
Fig. 1. TEM images of (a) H-0, (b) H-0.1, (c) H-0.3, and (d) H-0.5.
Please cite this article as: C. Tao, et al., Hydrophobic antireflective coatings with ultralow refractive index synthesized by deposition of methylated hollow silica nanoparticles, Mater Lett (2016), http://dx.doi.org/10.1016/j.matlet.2016.07.042i
376
C. Tao et al. / Materials Letters 183 (2016) 374–377
electron microscope (TEM) images taken with a Tecnai G2 F20 S-TWIN transmission electron microscope operated at an acceleration voltage of 200 kV. The surface morphologies of silica coatings were investigated using a Zeiss Supra55 field-emission scanning electron microscope. Atomic force microscopy (AFM) study (noncontact mode) of the films was made by a SPA-300HV Scanning Probe Microscope. Water contact angles of surfaces were measured at ambient temperature on a JC2000C contact angle/ interface system (Shanghai Zhongchen Digital Technique Apparatus Co.) using 4 μL water droplets. The thickness and refractive indices of the films deposited on silicon substrates were measured by a spectroscopic Ellipsometer (SENTECH SE850 UV), using the Cauchy model (n(λ)¼A þ B/λ2 þC/λ4) in the experimental range (400 nm to 800 nm) at an incidence angle of 70°. The transmittance spectra of the AR coatings were measured by an UV-Vis-NIR (Mapada, UV-3100PC).
3. Results and discussion 3.1. Morphology and structure of HSNs As shown in Fig. 1a, the mean diameter and shell thickness of HSNs are measured to be ca. 45 78 nm and ca. 107 3 nm, respectively. When MTES was added into the sols, the deposition of the methylated layer on the HSNs was formed through the hydrolysis and polycondensation reaction of MTES. The thickness of the MTES shell could be conveniently tuned by changing the MTES content. These methylated sols are stable without any precipitation for more than nine months. With low values of MTES/TEOS, the HSNs are monodispersed, which can be clearly distinguished in Fig. 1a, b. As MTES/TEOS increases, the HSNs are covered by a
less dark thin shell on the HSNs, which is considered as the formation of methylated shell upon the MTES addition (Fig. 1c, d). Moreover, the boundary of the HSNs gradually declines and aggregates form by the accumulation of HSNs with a low polarity. It can be well explained by the controlled aggregation mechanism of Bogush and Zukoski [12]; the particles in the sol grow by the aggregation of subparticles and once the particles have reached a certain size, the sol attains a colloidal stability as a result of the surface potential. 3.2. Effect of the MTES/TEOS on refractive indices, hydrophobicity, AR properties of the coatings The refractive indices of these coatings are plotted with the wavelength from 400 nm to 800 nm in Fig. 2a. F-0 has a low refractive index of 1.15 at 632.8 nm. Fig. 2b shows the refractive indices (at 632.8 nm) and porosity of the resultant coatings versus MTES/TEOS in the sols. With increasing of the MTES/TEOS to 0.7, the refractive index decreases rapidly to an ultralow value (n¼ 1.09), indicating a direct correlation between MTES/TEOS and the refractive index of the coating. It is the Si-CH3 groups that partially substituted the Si-OH on the H-0, resulting in a decrease in the intermolecular forces, which leads to a relatively low stacking density. The aggregation of the HSNs (Fig. S1), which led to the enlargement of the nanoparticles, may also play an important role in the decrease of the refractive indices of the coatings [13], as shown in Fig. S1. However, there is a slight increase for the F-0.9 (n ¼1.10). This is because the free MTES monomers in the S-0.9 can polymerize and act as some kind of filler in the pores between HSNs and decrease the porosity. The porosity of the coatings (between 80% and 62%) was calculated from the refractive index based on the Lorentz-Lorenz relationship [14], as shown in
Fig. 2. (a) Measured refractive indices of the films as a function of the wavelength; (b) Effect of MTES/TEOS on refractive index (at a wavelength of 632.8 nm) and porosity; (c) Effect of MTES/TEOS on film thickness and water contact angle of HSNs thin film; (d) Transmission spectra of a bare K9 glass, F-0, F-0.1, F-0.3, and F-0.5.
Please cite this article as: C. Tao, et al., Hydrophobic antireflective coatings with ultralow refractive index synthesized by deposition of methylated hollow silica nanoparticles, Mater Lett (2016), http://dx.doi.org/10.1016/j.matlet.2016.07.042i
C. Tao et al. / Materials Letters 183 (2016) 374–377
377
Fig. 3. AMF images of (a) F-0.1, (b) F-0.3, and (c) F-0.5.
Fig. 2b. Furthermore, the film thickness is presented in Fig. 2c, which is about 110 nm. The hydrophobic nature of silica thin films is closely linked to the AR stability of AR coatings [15]. The WCAs of the coatings (Fig. 2c) are 29.0°, 82.5°, 100.0°, 116.0°, and 122.5°, respectively. Methyls are known as hydrophobic groups with low polarity, and would rouse an increasing of WCAs when they are incorporated in coatings. AFM observations (Fig. 3) demonstrate that the rootmean-square (RMS) roughness of F-0.1, F-0.3, and F-0.5 is 26.6 nm, 29.3 nm and 36.2 nm, respectively, which is conducive to establish a hydrophobic surface with high surface roughness [16]. Due to apparently lower refractive indices of the films than that of bulk silica materials, they show relatively excellent AR properties. To illustrate the AR performance of these coatings, the transmittance spectra were measured, and are shown in Fig. 2d. The uncoated K9 substrates transmit about 92% of the light between 400 nm and 1200 nm wavelength. This value increases to about 97% transmission when the HSNs coatings are present, clearly indicating their AR properties. However, as the AR coatings were non-absorbing in nature, it was expected that the scattering of light originating from the relatively high surface roughness was mainly responsible for the loss of transmission.
4. Conclusions AR coatings were prepared from HSNs sols via the sol-gel process. Ellipsometry proves that the refractive index can be tuned between 1.09 and 1.15 by changing the MTES/TEOS. The introduction of methyl groups on HSNs improves the hydrophobicity and thus the AR stability of the coatings. This hydrophobic coating may have great application potential and good development prospective.
Acknowledgments We gratefully acknowledge the financial support by the National Natural Science Foundation of China (Grant No. 61405180, 51502274).
Appendix A. Supplementary material Supplementary data associated with this article can be found in the online version at http://dx.doi.org/10.1016/j.matlet.2016.07. 042.
References [1] W.W. Dou, P. Wang, D. Zhang, J.Q. Yu, An efficient way to prepare hydrophobic antireflective SiO2 film by sol-gel method, Mater. Lett. 167 (2016) 69–72. [2] J.Q. Xi, M.F. Schubert, J.K. Kim, E.F. Schubert, M. Chen, S.Y. Lin, W. Liu, J. A. Smart, Optical thin-film materials with low refractive index for broadband elimination of Fresnel reflection, Nat. Photonics 1 (2007) 176–179. [3] L.H. Yan, F.Q. Dong, S.N. Zhao, H.W. Yan, H.B. Lv, X.D. Yuan, Hydrophobic MgF2 antireflective films with enhanced environmental durability by a sol-gel process, Mater. Lett. 129 (2014) 156–158. [4] M.C.Y. Huang, Y. Zhou, C.J. Chang-Hasnain, A surface-emitting laser incorporating a high-index-contrast subwavelength grating, Nat. Photonics 1 (2007) 119–122. [4] L.Q. Liu, X.L. Wang, M. Jing, S.Q. Zhang, G.Y. Zhang, S.X. Dou, G. Wang, Broadband and omnidirectional, nearly zero reflective photovoltaic glass, Adv. Mater. 24 (2012) 6318–6322. [6] F.T. Chi, L.G. Yan, H.W. Yan, B. Jiang, H.B. Lv, X.D. Yuan, Ultralow-refractiveindex optical thin films through nanoscale etching of ordered mesoporous silica films, Opt. Lett. 37 (2012) 1406–1408. [7] M. Matheron, A. Bourgeois, A. Brunet-Bruneau, P.A. Albouy, J. Biteau, T. Gacoin, J.P. Boilot, Highly ordered CTAB-templated organosilicate films, J. Mater. Chem. 15 (2005) 4741–4745. [8] J.Q. Xi, J.K. Kim, E.F. Schubert, Silica nanorod-array films with very low refractive indices, Nano Lett. 5 (2005) 1385–1387. [9] A.L. Penard, T. Gacion, J.P. Boilot, Functionalized sol–gel coatings for optical applications, Acc. Chem. Res. 40 (2007) 895–902. [10] Y. Du, L.E. Luna, W.S. Tan, M.F. Rubner, R.E. Cohen, Hollow silica nanoparticles in UV–visible antireflection coatings for poly(methyl methacrylate) substrates, ACS Nano 4 (2010) 4308–4316. [11] C.Y. Tao, H.W. Yan, X.D. Yuan, C.Z. Yao, Q. Yin, J.Y. Zhu, W. Ni, L.H. Yan, L. Zhang, Synthesis of shape-controlled hollow silica nanostructures with a simple softtemplating method and their application as superhydrophobic antireflective coatings with ultralow refractive indices, Colloids Surf. A 7 (2016) 17–23. [12] G.H. Bogush, C.F. Zukoski IV, Uniform silica particle precipitation: an aggregative growth model, J. Colloid Interface Sci. 142 (1991) 1–18. [13] C.Y. Tao, H.W. Yan, X.D. Yuan, Q. Yin, J.Y. Zhu, W. Ni, L.H. Yan, L. Zhang, Detailed analysis and formation mechanism of superhydrophobic antireflective coatings with adjustable refractive index from trimethylsilanized silica nanoparticles, J. Sol-Gel Sci. Technol. (2016), http://dx.doi.org/10.1007/ s10971-016-4056-6. [14] M. Born, E. Wolf, Principles of Optics, Pergamon, New York, 1980. [15] S. Kim, J. Cho, K. Char, Thermally stable antireflective coatings based on nanoporous organosilicate thin films, Langmuir 23 (2007) 6737–6743. [16] T.L. Sun, L. Feng, X.F. Gao, L. Jiang, Bioinspired surfaces with special wettability, Acc. Chem. Res. 38 (2005) 644–652.
Please cite this article as: C. Tao, et al., Hydrophobic antireflective coatings with ultralow refractive index synthesized by deposition of methylated hollow silica nanoparticles, Mater Lett (2016), http://dx.doi.org/10.1016/j.matlet.2016.07.042i
Contents lists available at ScienceDirect
Materials Letters journal homepage: www.elsevier.com/locate/matlet
Hydrophobic antireflective coatings with ultralow refractive index synthesized by deposition of methylated hollow silica nanoparticles Chaoyou Tao a,b, Hongwei Yan a, Xiaodong Yuan a, Qiang Yin a, Jiayi Zhu a, Wei Ni a, Lianghong Yan a, Lin Zhang a,n a b
Research Center of Laser Fusion, China Academy of Engineering Physics, Mianyang 621900, China Graduate School of China Academy of Engineering Physics, Beijing 100088, China
art ic l e i nf o
a b s t r a c t
Article history: Received 6 February 2016 Received in revised form 30 June 2016 Accepted 10 July 2016 Available online 12 July 2016
A new type of antireflective (AR) coating materials with easily tailorable refractive index were successfully prepared by the sol-gel method based on the deposition of colloidal hollow silica nanoparticles (HSNs). HSNs were synthesized using tetraethylorthosilicate (TEOS) as the precursor, and then modified by methyltriethoxysilane (MTES). It is found that the refractive index (n) can be precisely tuned between 1.15 and 1.09 by changing the MTES content, in a range that is not accessible to dense inorganic materials. AR properties of the coatings on K9 glasses were demonstrated. Furthermore, AR coatings are intrinsically hydrophobic with the water contact angle (WCA) up to 122.5°. & 2016 Elsevier B.V. All rights reserved.
Keywords: Antireflective Sol-gel preparation Thin films Ultralow refractive index Hydrophobicity
1. Introduction Nanoporous materials have been extensively exploited for antireflective (AR) coatings [1–3], and distributed Bragg reflectors [4]. However, the realization of practical devices with excellent optical properties has been hindered by the lack of optical materials with very low refractive indices, especially which closely matches the refractive index of air. Therefore, developing novel materials with refractive indices lower than that of conventional optically transparent materials has attracted a great deal of attention. Materials with n¼ 1.07 [5] and even n¼1.03 [6] have been obtained via chemical etching. The approach based on the burning off additional templates has been demonstrated to be effective in obtaining nanoporous layers [7]. Recently, two silica nanorod array films for broadband AR coatings with refractive indices as low as 1.08 and 1.05 have been fabricated via oblique-angle deposition process [2,8]. However, these methods involved either hazardous solvents, or high calcination temperatures, or expensive machines, which is disadvantageous to large-scale applications. It is well known that the sol-gel process is the most appealing method for the preparation of nanoporous materials because of its low process temperature, low cost, the high purity of the resulting materials and the availability of substrates with complex shapes n
Corresponding author. E-mail address: [email protected] (L. Zhang).
[9]. Though the formation of silica materials with a very low refractive index (n ¼1.11) has achieved [10], multifunctional coating materials with tunable and lower refractive index (o1.10), and hydrophobicity are highly desirable. The present contribution describes a novel method for the synthesis of hydrophobic silica AR coatings with an ultralow and easily tunable refractive index by the dip-coating deposition of hollow silica nanoparticles (HSNs). The approach is illustrated in Scheme 1. The effect of the MTES content on the HSNs, film morphology, refractive index, and hydrophobicity are discussed.
2. Experimental Tetraethoxysilicate (TEOS, 98þ %) was obtained from Alfa Aesar. Poly(acrylic acid) (PAA, M.W. 3000), methyltriethoxysilane (MTES) were purchased from Aladdin Chemistry. HSNs were prepared by the modified Stöber method [11]. Then varied MTES were added into the HSNs sols. These hybrid sols were stirred at 30 °C for 2 h and aged for 7 days to allow MTES to react fully. The weight ratio of MTES and TEOS (MTES/TEOS) ranged from 0 to 0.9. Samples of sols, HSNs were denoted as “S-A”, “HA”, respectively, in which A means MTES/TEOS. The sols were deposited on well-cleaned K9 glasses or silicon using the dip-coating process at a fixed withdrawal rate (1000 mm min 1). Samples of coatings were denoted as “F-A”. The morphologies of the HSNs were observed by transmission
http://dx.doi.org/10.1016/j.matlet.2016.07.042 0167-577X/& 2016 Elsevier B.V. All rights reserved.
Please cite this article as: C. Tao, et al., Hydrophobic antireflective coatings with ultralow refractive index synthesized by deposition of methylated hollow silica nanoparticles, Mater Lett (2016), http://dx.doi.org/10.1016/j.matlet.2016.07.042i
C. Tao et al. / Materials Letters 183 (2016) 374–377
375
Scheme 1. Schematic description of the developed synthesis method for hydrophobic HSNs films with tunable refractive index.
Fig. 1. TEM images of (a) H-0, (b) H-0.1, (c) H-0.3, and (d) H-0.5.
Please cite this article as: C. Tao, et al., Hydrophobic antireflective coatings with ultralow refractive index synthesized by deposition of methylated hollow silica nanoparticles, Mater Lett (2016), http://dx.doi.org/10.1016/j.matlet.2016.07.042i
376
C. Tao et al. / Materials Letters 183 (2016) 374–377
electron microscope (TEM) images taken with a Tecnai G2 F20 S-TWIN transmission electron microscope operated at an acceleration voltage of 200 kV. The surface morphologies of silica coatings were investigated using a Zeiss Supra55 field-emission scanning electron microscope. Atomic force microscopy (AFM) study (noncontact mode) of the films was made by a SPA-300HV Scanning Probe Microscope. Water contact angles of surfaces were measured at ambient temperature on a JC2000C contact angle/ interface system (Shanghai Zhongchen Digital Technique Apparatus Co.) using 4 μL water droplets. The thickness and refractive indices of the films deposited on silicon substrates were measured by a spectroscopic Ellipsometer (SENTECH SE850 UV), using the Cauchy model (n(λ)¼A þ B/λ2 þC/λ4) in the experimental range (400 nm to 800 nm) at an incidence angle of 70°. The transmittance spectra of the AR coatings were measured by an UV-Vis-NIR (Mapada, UV-3100PC).
3. Results and discussion 3.1. Morphology and structure of HSNs As shown in Fig. 1a, the mean diameter and shell thickness of HSNs are measured to be ca. 45 78 nm and ca. 107 3 nm, respectively. When MTES was added into the sols, the deposition of the methylated layer on the HSNs was formed through the hydrolysis and polycondensation reaction of MTES. The thickness of the MTES shell could be conveniently tuned by changing the MTES content. These methylated sols are stable without any precipitation for more than nine months. With low values of MTES/TEOS, the HSNs are monodispersed, which can be clearly distinguished in Fig. 1a, b. As MTES/TEOS increases, the HSNs are covered by a
less dark thin shell on the HSNs, which is considered as the formation of methylated shell upon the MTES addition (Fig. 1c, d). Moreover, the boundary of the HSNs gradually declines and aggregates form by the accumulation of HSNs with a low polarity. It can be well explained by the controlled aggregation mechanism of Bogush and Zukoski [12]; the particles in the sol grow by the aggregation of subparticles and once the particles have reached a certain size, the sol attains a colloidal stability as a result of the surface potential. 3.2. Effect of the MTES/TEOS on refractive indices, hydrophobicity, AR properties of the coatings The refractive indices of these coatings are plotted with the wavelength from 400 nm to 800 nm in Fig. 2a. F-0 has a low refractive index of 1.15 at 632.8 nm. Fig. 2b shows the refractive indices (at 632.8 nm) and porosity of the resultant coatings versus MTES/TEOS in the sols. With increasing of the MTES/TEOS to 0.7, the refractive index decreases rapidly to an ultralow value (n¼ 1.09), indicating a direct correlation between MTES/TEOS and the refractive index of the coating. It is the Si-CH3 groups that partially substituted the Si-OH on the H-0, resulting in a decrease in the intermolecular forces, which leads to a relatively low stacking density. The aggregation of the HSNs (Fig. S1), which led to the enlargement of the nanoparticles, may also play an important role in the decrease of the refractive indices of the coatings [13], as shown in Fig. S1. However, there is a slight increase for the F-0.9 (n ¼1.10). This is because the free MTES monomers in the S-0.9 can polymerize and act as some kind of filler in the pores between HSNs and decrease the porosity. The porosity of the coatings (between 80% and 62%) was calculated from the refractive index based on the Lorentz-Lorenz relationship [14], as shown in
Fig. 2. (a) Measured refractive indices of the films as a function of the wavelength; (b) Effect of MTES/TEOS on refractive index (at a wavelength of 632.8 nm) and porosity; (c) Effect of MTES/TEOS on film thickness and water contact angle of HSNs thin film; (d) Transmission spectra of a bare K9 glass, F-0, F-0.1, F-0.3, and F-0.5.
Please cite this article as: C. Tao, et al., Hydrophobic antireflective coatings with ultralow refractive index synthesized by deposition of methylated hollow silica nanoparticles, Mater Lett (2016), http://dx.doi.org/10.1016/j.matlet.2016.07.042i
C. Tao et al. / Materials Letters 183 (2016) 374–377
377
Fig. 3. AMF images of (a) F-0.1, (b) F-0.3, and (c) F-0.5.
Fig. 2b. Furthermore, the film thickness is presented in Fig. 2c, which is about 110 nm. The hydrophobic nature of silica thin films is closely linked to the AR stability of AR coatings [15]. The WCAs of the coatings (Fig. 2c) are 29.0°, 82.5°, 100.0°, 116.0°, and 122.5°, respectively. Methyls are known as hydrophobic groups with low polarity, and would rouse an increasing of WCAs when they are incorporated in coatings. AFM observations (Fig. 3) demonstrate that the rootmean-square (RMS) roughness of F-0.1, F-0.3, and F-0.5 is 26.6 nm, 29.3 nm and 36.2 nm, respectively, which is conducive to establish a hydrophobic surface with high surface roughness [16]. Due to apparently lower refractive indices of the films than that of bulk silica materials, they show relatively excellent AR properties. To illustrate the AR performance of these coatings, the transmittance spectra were measured, and are shown in Fig. 2d. The uncoated K9 substrates transmit about 92% of the light between 400 nm and 1200 nm wavelength. This value increases to about 97% transmission when the HSNs coatings are present, clearly indicating their AR properties. However, as the AR coatings were non-absorbing in nature, it was expected that the scattering of light originating from the relatively high surface roughness was mainly responsible for the loss of transmission.
4. Conclusions AR coatings were prepared from HSNs sols via the sol-gel process. Ellipsometry proves that the refractive index can be tuned between 1.09 and 1.15 by changing the MTES/TEOS. The introduction of methyl groups on HSNs improves the hydrophobicity and thus the AR stability of the coatings. This hydrophobic coating may have great application potential and good development prospective.
Acknowledgments We gratefully acknowledge the financial support by the National Natural Science Foundation of China (Grant No. 61405180, 51502274).
Appendix A. Supplementary material Supplementary data associated with this article can be found in the online version at http://dx.doi.org/10.1016/j.matlet.2016.07. 042.
References [1] W.W. Dou, P. Wang, D. Zhang, J.Q. Yu, An efficient way to prepare hydrophobic antireflective SiO2 film by sol-gel method, Mater. Lett. 167 (2016) 69–72. [2] J.Q. Xi, M.F. Schubert, J.K. Kim, E.F. Schubert, M. Chen, S.Y. Lin, W. Liu, J. A. Smart, Optical thin-film materials with low refractive index for broadband elimination of Fresnel reflection, Nat. Photonics 1 (2007) 176–179. [3] L.H. Yan, F.Q. Dong, S.N. Zhao, H.W. Yan, H.B. Lv, X.D. Yuan, Hydrophobic MgF2 antireflective films with enhanced environmental durability by a sol-gel process, Mater. Lett. 129 (2014) 156–158. [4] M.C.Y. Huang, Y. Zhou, C.J. Chang-Hasnain, A surface-emitting laser incorporating a high-index-contrast subwavelength grating, Nat. Photonics 1 (2007) 119–122. [4] L.Q. Liu, X.L. Wang, M. Jing, S.Q. Zhang, G.Y. Zhang, S.X. Dou, G. Wang, Broadband and omnidirectional, nearly zero reflective photovoltaic glass, Adv. Mater. 24 (2012) 6318–6322. [6] F.T. Chi, L.G. Yan, H.W. Yan, B. Jiang, H.B. Lv, X.D. Yuan, Ultralow-refractiveindex optical thin films through nanoscale etching of ordered mesoporous silica films, Opt. Lett. 37 (2012) 1406–1408. [7] M. Matheron, A. Bourgeois, A. Brunet-Bruneau, P.A. Albouy, J. Biteau, T. Gacoin, J.P. Boilot, Highly ordered CTAB-templated organosilicate films, J. Mater. Chem. 15 (2005) 4741–4745. [8] J.Q. Xi, J.K. Kim, E.F. Schubert, Silica nanorod-array films with very low refractive indices, Nano Lett. 5 (2005) 1385–1387. [9] A.L. Penard, T. Gacion, J.P. Boilot, Functionalized sol–gel coatings for optical applications, Acc. Chem. Res. 40 (2007) 895–902. [10] Y. Du, L.E. Luna, W.S. Tan, M.F. Rubner, R.E. Cohen, Hollow silica nanoparticles in UV–visible antireflection coatings for poly(methyl methacrylate) substrates, ACS Nano 4 (2010) 4308–4316. [11] C.Y. Tao, H.W. Yan, X.D. Yuan, C.Z. Yao, Q. Yin, J.Y. Zhu, W. Ni, L.H. Yan, L. Zhang, Synthesis of shape-controlled hollow silica nanostructures with a simple softtemplating method and their application as superhydrophobic antireflective coatings with ultralow refractive indices, Colloids Surf. A 7 (2016) 17–23. [12] G.H. Bogush, C.F. Zukoski IV, Uniform silica particle precipitation: an aggregative growth model, J. Colloid Interface Sci. 142 (1991) 1–18. [13] C.Y. Tao, H.W. Yan, X.D. Yuan, Q. Yin, J.Y. Zhu, W. Ni, L.H. Yan, L. Zhang, Detailed analysis and formation mechanism of superhydrophobic antireflective coatings with adjustable refractive index from trimethylsilanized silica nanoparticles, J. Sol-Gel Sci. Technol. (2016), http://dx.doi.org/10.1007/ s10971-016-4056-6. [14] M. Born, E. Wolf, Principles of Optics, Pergamon, New York, 1980. [15] S. Kim, J. Cho, K. Char, Thermally stable antireflective coatings based on nanoporous organosilicate thin films, Langmuir 23 (2007) 6737–6743. [16] T.L. Sun, L. Feng, X.F. Gao, L. Jiang, Bioinspired surfaces with special wettability, Acc. Chem. Res. 38 (2005) 644–652.
Please cite this article as: C. Tao, et al., Hydrophobic antireflective coatings with ultralow refractive index synthesized by deposition of methylated hollow silica nanoparticles, Mater Lett (2016), http://dx.doi.org/10.1016/j.matlet.2016.07.042i