Sol-gel Preparation of Superhydrophilic Silica Coating-materials with Low Refractive Index†

doi:10.7503/cjcu20170606

Abstract

Abstract:

Porous silica coatings with low refractive index and superhydrophilicity property were prepared via a base-catalysed sol-gel process. Precursor sols were prepared based on a base-catalysed sol-gel process, followed by etching of silica particles in sols with acid fluoride(HF). Then, low refractive index films were prepared by dip-coating process. It was found that the refractive index of coating reduce to 1.101 after etching with 3% HF, the static contact angle of the films reduced to 3° and anti-fogging performance of the coatings is improved significantly.

Key words: Low refractive index, Sol-gel method, Superhydrophilic, Anti-fogging performance, Acid fluoride, Etching of silica particles

CLC Number:

O631

TrendMD:

ZHANG Shuming, LUO Jianhui, XIA Bibo, LI Yuanyang, HE Meiying, JIANG Bo. Sol-gel Preparation of Superhydrophilic Silica Coating-materials with Low Refractive Index^†[J]. Chem. J. Chinese Universities, 2018, 39(6): 1342.

Figures/Tables 10

Table 1 Optical parameters of HF and SiO2 sol with varing mass fraction

θ(%)	n	T_max(%)	θ(%)	n	T_max(%)
0	1.210	99.92	4	1.119	98.15
1	—	—	5	1.137	98.50
2	—	—	6	—	—
3	1.101	97.35

Fig.1 Measured transmittance spectrum of HF-SiO2 coatings with θ=3%(a) and the simulated spectrum of coatings with n=1.101(b)Inset: the dispersion curve of the corresponding coatings.

Fig.2 Nitrogen adsorption isotherms(A) and pore size distributions(B) for HF-SiO2 xerogels of different θθ(%): a. 0; b. 3; c. 4; d. 5. The adsorption isotherms of θ=3%, 4% and 5% are shifted by 800, 600 and 400 cm3/g STP, respectively.

Table 2 Deduced porosity and refractive index(n)

θ(%)	Measured BET data		Calculated data		Measured n (at 633 nm)
θ(%)	Pore size/nm	Pore volume/(mL·g^-1)	Porosity ρ(%)	n_ρ	Measured n (at 633 nm)
0	1.76	0.6852	61.28	1.198	1.210
3	5.32	1.7430	80.01	1.106	1.101
4	4.24	1.4270	76.72	1.123	1.119
5	3.35	1.2490	74.26	1.135	1.137

Table 3 Deduced porosity and refractive index

t/h	Measured BET data		Calculated data		Measured n (at 633 nm)
t/h	Pore size/nm	Pore volume/(mL·g^-1)	Porosity ρ(%)	n_ρ	Measured n (at 633 nm)
0	1.76	0.6852	61.28	1.198	1.210
2	4.03	1.6240	78.95	1.112	1.120
4	4.64	1.6970	79.67	1.108	1.107
6	5.32	1.7430	80.01	1.106	1.101
8	5.34	1.7510	80.02	1.105	1.101

Fig.3 FTIR spectra of SiO2 xerogels(a) and 3% HF-SiO2 xerogels(b)

Fig.4 TEM image of SiO2 sol particles(A), TEM(B), SEM cross-section (C) and AFM coating(D) images of 3% HF-SiO2 sol particles

Scheme 1 Schematic illustration of the formation mechanisms of coatings

Fig.5 Model of particles in SiO2 sol(A) and in 3%HF-SiO2(B) and corresponding static contact angle images

Fig.6 Fogging behavior of a bare glass slide(A), a glass slide covered by SiO2 sol(B) and a glass slide covered by 3%HF-SiO2(C)

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