Article pubs.acs.org/Langmuir
Transparent, Superhydrophobic, and Wear-Resistant Coatings on Glass and Polymer Substrates Using SiO2, ZnO, and ITO Nanoparticles Daniel Ebert and Bharat Bhushan* Nanoprobe Laboratory for Bio- & Nanotechnology and Biomimetics (NLBB), The Ohio State University, 201 W. 19th Avenue Columbus, Ohio 43210-1142, United States ABSTRACT: It is of significant interest to create surfaces that simultaneously exhibit high water contact angle, low contact angle hysteresis, and high transmission of visible light, as well as mechanical wear resistance for industrial applications. The fabrication of such surfaces has often involved complex or expensive processes, required techniques that were not suitable for a variety of substrates and particles, required surface posttreatment, or lacked wear resistance. A systematic study has been performed in which transparent superhydrophobic surfaces were created on glass, polycarbonate, and poly(methyl methacrylate) (PMMA) substrates using surface-functionalized SiO2, ZnO, and indium tin oxide (ITO) nanoparticles. The contact angle, contact angle hysteresis, and optical transmittance were measured for samples using all particle−substrate combinations. To examine wear resistance, multiscale wear experiments were performed using an atomic force microscope (AFM) and a water jet apparatus.
1. INTRODUCTION
exceed roughly one-quarter of the wavelength of visible light (around 100 nm or less).5−10 Whereas glass is the most common optical material for lenses, architectural windows, and so forth, transparent polymers such as polycarbonate (PC) and poly(methyl methacrylate) (PMMA) are also of great engineering importance. PC and PMMA are used for wide-ranging applications such as aircraft canopies, bullet-proof windows, solar cell panels, laptop computer screens, and many high-performance optical, electronic, and medical devices. SiO2, ZnO, and ITO thin films are of interest for varying applications. Select properties and potential benefits of SiO2, ZnO, and ITO are shown in Table 1. The three metal oxides have high transmittance for visible light due to low refractive indices
Interest in superhydrophobic surfaces (typically defined as having a water contact angle (CA) greater than 150° and contact angle hysteresis (CAH) less than 10°) has grown rapidly in recent years due to unique characteristics such as self-cleaning, antifouling, and fluid drag reduction. 1−3 However, for applications such as self-cleaning windows, optical devices, and solar panels, high optical transparency is additionally required, as well as resistance to mechanical wear. For example, typical requirements for an automotive windshield are visible transmittance >90%, haze 10° 5°
∼82% 85% 94% 93% 100%
waterfall
35 36 8 37 38
