It might seem counterintuitive, but MIT researchers have created a glass whose rough finish–at least at the microscopic level–helps keep it clean, glare-free and fog-resistant. To achieve this surface, the glass is repeatedly coated with a fine layer of material that is later partially removed, leaving behind nanoscale pillars, or cones, that are five times as tall as their 200-nanometer bases.
It would seem that this “nubby” glass would do just the opposite–that it would, like coarse fabrics, attract and hold water, dirt and debris. But the MIT scientists say no. The pebbled or pillared finish, described as super-hydrophobic (fearing or hating fluid) in a paper written by the researchers–Kyoo-Chul Park, Hyungryul Choi, former postdoc Chih-Hao Chang and professors Robert Cohen, Gareth McKinley and George Barbastathis–is also capable of omnidirectional broadband super-transmissivity of more than 98 percent over a wide range of frequencies and solar collector angles. That means it reflects very little light.
In future, these same researchers hope to be able to commercialize their discovery via low-cost fabrication and apply it to a wide range of products that would benefit from the advance, namely optical devices (ranging from cameras to eyeglasses), the screens of electronic handheld devices, television screens, car windshields, even building windows, removing the need for window washers to hang suspended thirty stories off the ground just waiting for storms and high winds to strike (eeek!).
Perhaps more important, the self-cleaning glass would improve the efficiency of huge solar photovoltaic “farms,” where thousands of solar panels gradually accumulate dust, debris and even bird droppings and as a result lose up to 40 percent of their nameplate efficiency. The textured surface would also improve the collection of the sun’s rays, as witness the rows of pyramid-shaped solar collectors that, because of their various planes, collect more sunlight than flat sheets of glass, especially in the morning and evening, when the oblique angle of the sun (to the earth) means solar glass is reflecting rather than capturing light. In fact, given that the glass’s texture is more important than any process used to generate it, Park and Choi envision a future when glass can be passed through texturizing rollers while still partially molten, thus cutting deposition and etching costs to the bone.