Facile fabrication of antifogging, antireflective, and self-cleaning transparent silica thin coatings

Highlights

• A multifunctional silica nanoparticles thin (SNT) coating was fabricated.

• The roughness test showed that the morphology related closely to the deposition time.

• The nanostructure endow the coating with superhydrophilicity without further chemical modification.

• The antifogging property of the SNT coating was investigated.

• The SNT coating possesses the properties of antireflection and self-clean.

Abstract

We have fabricated a multifunctional coating with properties of superhydrophilicity, high transparency, antireflection and self-clean via a low-cost one-step chemical vapor deposition method without any further chemical modification. We have investigated influence of the surface topography of the silica nanoparticles to the antifogging and antireflection. The results have indicated that the excellent antifogging and transparency properties are due to the amplification of the well-ordered nipple silica nanoparticles to the hydrophilicity and suppression of the reflection, respectively. Moreover, the superhydrophilicity have endowed the coating with self-cleaning property.

Introduction

In recent years, coatings with superhydrophobicity [1], [2], [3], [4] or superhydrophilicity [5], [6], [7], [8], [9], [10], [11], [12], [13] are designed to prevent the formation of fog by controlling the interaction of liquids with surfaces. It has been demonstrated that the superwetting and superhydrophobic surface can hardly be achieved by surface chemistry alone. The fabrication of hierarchical structure plays significant influences on the surface wettability. Therefore, to achieve the antifogging properties for antireflective coatings, both surface chemical modification and micro/nano texturing are necessary [14], [15].

As well known, an ideal superhydrophobic surface is non-wettable completely with a water contact angle >150° and a low contact angle hysteresis [16]. When fog occurred, globular droplet can slide away from the surface effortlessly due to the low sliding angle or tiny external force, which makes the superhydrophobic surface a promising candidate for antifogging materials. For instance, Kyoo-Chul Park and his co-workers fabricated a multifunctional surface with tapered conical nanotextures via deposition and photoetching followed by a chemical vapor deposition of 1H,1H,2H,2H-perfluorodecyl-trichlorosilane [17]. The nanocone surface was surperhydrophobic and transparent with very weak reflection. Nevertheless, when amounts of water vapor appear in seconds, the adhesion of tiny water droplets is an intractable problem.

In contrast to the superhydrophobic surface, water droplets would spontaneously spread on the superhydrophilic surfaces (water contact angle <5° within 0.5 s or less) and form a nearly continuous water film [16]. The thin water film assists light to transmit directly and decreases the scattering from water microdroplets [4], [18]. Howarter et al. grafted hydrophilic poly (ethylene glycol) (PEG), onto a glass surface by a silane-type coupling agent [8]. By this method, superhydrophilic surfaces with good adhesion were successfully achieved. Lee et al. prepared a superhydrophilic surface by using hydrogen-bonding-assisted layer-by-layer assembly of poly (vinyl alcohol) (PVA) and poly (acrylic acid) (PAA) with excellent antifogging and frost-resistant properties [9]. Although these superhydrophilic polymer coatings perform satisfactorily in antifogging, such high energy surfaces are easily contaminated by dust so as to lower their surface free energy and these superhydrophilic surfaces do not retain their properties for long time. In addition, the long response time, swelling and low strength of the polymer coating restrict their applications in antifogging.

In fact, textured micro or nanoporous structures construction is a promising way to create a stable superhydrophilic surface [19]. In recent studies, the top-down fabrication and bottom-up approach are widely used to fabricate such surfaces [20], [21], [22]. Fujima et al. developed a hierarchical nanoporous layer on silicate glass by a one-pot etching method [20]. Samples retained a superhydrophilic surface (water contact angle of approximately 5°) for more than 140 days and exhibited a commendable antifogging property. Jia et al. fabricated a hydrophilic SiO₂ nanofibrous film on plain glass by the seedless flame spray pyrolysis method [15]. Combining the hydrophilicity of SiO₂ and the rough fibrous structure, the nanofibrous SiO₂ film exhibited considerable anti-fogging and anti-reflective properties.

Antireflective coatings (ARCs) with micro/nano structure [23], [24], [25] are fabricated and widely used in architectural windows, glasses, solar cells [26], [27], photovoltaic modules and display devices to enhance the transparency performance of these equipments. In nature, some insects have excellent optical properties due to the multi-scale structures. By mimicking the structure of the insect, lots of antireflective coatings are fabricated [28], [29]. Du et al. fabricated hollow mesoporous silica nanospheres using layer-by-layer dip-coating, and these materials exhibited a significant reduction in the reflection from the visible to the near-infrared regions [30]. Zhang et al. developed an antireflective coating with a closed-pore structure by a low cost sol-gel dip-coating method [31]. This nanocomposite single-layered antireflection coating showed a reduction in the reflectance (6.29%) and an improvement in the transmittance (6.07%), as compared with the bare solar glass. However, to date, the maximum transmittance of the various antireflective films was relatively low in optical field. Besides, the fog formed by the water vapor condenses onto the surface of transparent substrate will scatter light and reduce optical transmission of the transparent materials. Therefore, the ARCs with function of antifogging are imperative to reduce the scattering of light caused by the fog.

Herein, we demonstrate a strategy based on the roughness and regular convex nipple structure. In this study, well-ordered nipple silica nanoparticles structures were successfully fabricated via a facile one-step chemical vapor deposition. This method allows good control of the morphology of the nanostructures and is also feasible for low-cost, large-scale production. The surface properties, including the surface wettability, anti-fogging and antireflective properties, of the silica nanoparticles thin (SNT) coatings were studied to explore their potential multifunctional applications.