High transparency is important to the performance of optical equipment and devices, such as windows, lenses, solar panels, and safety goggles. As many of them are constantly exposed to various environmental conditions, it is highly desirable to develop a self-cleaning coating that can prevent microbial growth, fouling, corrosion and icing. One of these technologies is superhydrophobic coating.In this review, we discuss recent progress in design, synthesis and fabrication of transparent, superhydrophobic surfaces. First, we revisit different models of superhydrophobicity and present the potential challenges in the nanofabrication of transparent superhydrophobic surfaces. We then discuss the general fabrication methods, including the top-down fabrication methods and self-assembly approaches, to create roughness with a size in the sub-visible wavelength with or without posthydrophobilization steps. While top-down fabrication offers well-defined size and shape of surface topography, self-assembly is more versatile and could enable mass-production of nano-roughness on a wide range of substrates at a lower cost. Therefore, we focus on discussion of different self-assembly methods, including sol-gel processes, microphase separation, templating, and nanoparticle assembly, to create transparent, superhydrophobic surfaces. The review concludes with perspectives on future directions and challenges in manipulation of surface nanoroughness, specifically, using nanoparticles, for both high transparency and superhydrophobicity and their potential applications.

Transparent and superamphiphobic coatings that repel both water and low‐surface‐tension oil offer energy and environmental benefits to building windows, solar cell panels, electronic displays, and other optical equipment. Here, we developed a solution consisting of stringed amphiphilic silica nanoparticles (NPs) and an amphiphilic sol, which could be spray coated onto a variety of planar and curved substrates in one step. High transparency, water/oil contact angles greater than 150° and roll‐off angles less than 10° were demonstrated. The stringed NPs formed a fractal‐like nanoporous network, while the sol acted as a surface modifier and binder to enhance the coating robustness against heating (up to 400 °C), water jetting, and sand abrasion.

We present a simple two-step method to fabricate dual-scale superhydrophobic surfaces by using replica molding of poly(dimethylsiloxane) (PDMS) micropillars, followed by deposition of a thin, hard coating layer of a SiO(x)-incorporated diamond-like carbon (DLC). The resulting surface consists of microscale PDMS pillars covered by nanoscale wrinkles that are induced by residual compressive stress of the DLC coating and a difference in elastic moduli between DLC and PDMS without any external stretching or thermal contraction on the PDMS substrate. We show that the surface exhibits superhydrophobic properties with a static contact angle over 160 degrees for micropillar spacing ratios (interpillar gap divided by diameter) less than 4. A transition of the wetting angle to approximately 130 degrees occurs for larger spacing ratios, changing the wetting from a Cassie-Cassie state (C(m)-C(n)) to a Wenzel-Cassie state (W(m)-C(n)), where m and n denote micro- and nanoscale roughness, respectively. The robust superhydrophobicity of the Cassie-Cassie state is attributed to stability of the Cassie state on the nanoscale wrinkle structures of the hydrophobic DLC coating, which is further explained by a simple mathematical theory on wetting states with decoupling of nano- and microscale roughness in dual scale structures.

Transparent, superamphiphobic surfaces that repel both water and oils are prepared from mushroom-like micropillar arrays consisting of nanoparticles only at the top of the pillars by controlled compartment filling of silica nanoparticles into the bottom of the poly(dimethylsiloxane) (PDMS) mold, followed by infiltration of epoxy and UV curing. Because silica nanoparticle decorated pillar heads are more resistant to O2 plasma than the polymer pillars, we can precisely control the head size of micropillars and nanoroughness on top of the pillar heads by varying the O2 plasma time. The combination of nanoroughness and mushroom-like micropillars leads to superhydrophobicity and oil repellency to different organic solvents. High transparency is achieved by increasing the spacing ratio of micropillars. Last, we demonstrate anisotropic wetting on the hierarchical surface can be achieved by combining photolithography, replica molding, and self-assembly techniques.