Ever since Apple asked Corning to build scratchless glass screens for the original iPhone, the development of glass has been a major focus in the technology world. Scientists continue to improve the glass-making process, devising new ways to make it thinner but stronger. Yet, glass suffers from a number of other inefficiencies: It doesn't handle water well, it reflects too much light, and it creates glare.
On Thursday, researchers at MIT announced a major breakthrough in glass-making technology, which basically involves a new way to create surface textures on glass to eliminate all of the drawbacks of glass, including unwanted reflections and glare. In fact, this new multifunctional glass is not only crystal clear -- unlike all other glass, which is reflective by nature -- but it also causes water droplets to bounce right off its surface, like tiny rubber balls.
The glass is self-cleaning, anti-reflective, and superhydrophobic. If it ever gets to be as strong as Corning's Gorilla Glass, MIT will have effectively created the perfect glass.
In the 34-page research paper, Kyoo-Chul Park, an MIT mechanical engineering grad student and a co-author of the study, explains that the idea to build multifunctional glass was inspired by nature, where different textured surfaces helped all kinds of living organisms, from desert beetles' carapaces to lotus leaves, evolve and survive in the wild. The team similarly wanted to build glass that could be adaptable to any environment.
Microscopic studies of the textured surfaces commonly encountered on living organisms, e.g. lotus leaves, desert beetles, and moth eyes, have revealed complementary roles of material properties and texture on the surface functionalities that have been developed during adaptation to different environments, the study said. Nature is an excellent architect for designing and optimizing surfaces that fulfill multiple purposes.
Park said that the surface properties only benefit the operational efficiency and longevity of the glass. But one of the best aspects of the glass is its inability to accumulate moisture. Park explains:
On rough surfaces, the wetting characteristics of water droplets can be explained through two distinct models, Park said. The Wenzel model describes sessile droplets that fully wet the surface texture. On the other hand, the Cassie-Baxter model describes water droplets that reside partially on the solid texture and partially on a raft of air pockets entrapped within the microscopic texture which enable the surface to become superhydrophobic. On such 'Cassie-Baxter surfaces', water droplets can easily roll or bounce off, leading to the ready removal of dust particles and contaminants.
In other words, while most glass surfaces only spread water around the glass, MIT's new superhydrophobic glass would be perfect for products such as swimming goggles and car windshields.
The new glass is great against water, but it also helps boost the efficiency of other glass-based tools and objects. For example, Park explains that photovoltaic cells can lose up to 40 percent of their efficiency within six months, usually due to dust and dirt accumulation; but with the new self-cleaning glass as a surface, a photovoltaic panel would not lose its efficiency over time, and it would also transmit much more light through its surface, making the cell much more powerful, especially when the sun's rays are at an angle. Without MIT's glass added to solar panels, the glass sometimes reflects as much as 50 percent of the sun's rays during the early morning and late afternoon hours.
Of course, MIT's glass could have other applications as well, including optical devices like TV screens, as well as smartphone and tablet displays, which would benefit from the self-cleaning ability of the glass by resisting contamination by sweat. Cameras and microscopes would benefit from the ability to offset humid conditions, and even windows in buildings could be a great application, even though it would be very dangerous for birds.
So what's behind this incredible glass technology? MIT's invention is created by a simple surface pattern, which consists of an array of nanoscale cones that are roughly five times as tall as their base width -- this method was adapted from techniques currently used in the semiconductor industry to coat and etch glass. The glass itself is coated with several thin layers, including a photoresistant layer that is illuminated with a grid pattern and then etched away. These etchings after each successive layer produce the conical shapes, which are completely responsible for the unique characteristics of the glass. Park said that the glass could be built by passing the surface features through partially-molten textured rollers, which would substantially cut down on the costs of manufacturing the glass.
Read more about the technology in the team's paper, which was published in the journal ACS Nano. The study was written by Park, as well as another mechanical engineering grad student Hyungryul Choi, former postdoc Chih-Hao Chang SM '04, PhD '08 (now at N.C. State University), chemical engineering professor Robert Cohen, and mechanical engineering professors Gareth McKinley and George Barbastathis.
The research was funded by the Army Research Office through MIT's Institute for Soldier Nanotechnology; the Air Force Office of Scientific Research; Singapore's National Research Foundation through the Singapore-MIT Alliance for Research and Technology (SMART) Centre, and the Xerox Foundation. Park and Choi are recipients of fellowships from Samsung and the Kwanjeong Educational Foundation/STX Scholarship Foundation, respectively.
The invention is still patent-pending.