These nanotextured surfaces are also robustly anti-fogging and self-cleaning offering potential benefits for applications
The “multifunctional” glass is created through a process that involves layers of material being deposited on a surface before being selectively etched away. The MIT team produced a surface covered with tiny cones, each five times taller than their width. This pattern in turn prevents reflections and repels water.
“Designing multifunctional surfaces that have user-specified interactions with impacting liquids and with incident light is a topic of both fundamental and practical significance,” the research paper states. “Taking cues from nature, we use tapered conical nanotextures to fabricate the multifunctional surfaces; the slender conical features result in large topographic roughness whilst the axial gradient in the effective refractive index minimizes reflection through adiabatic index-matching between air and the substrate.”
The ACS Nano journal, is co-authored by mechanical engineering graduate students Kyoo-Chul Park and Hyungryul Choi, former postdoc Chih-Hao Chang, chemical engineering professor Robert Cohen and mechanical engineering professors Gareth McKinley and George Barbastathis. The researchers explained the intricate details of the new technology:
“Precise geometric control of the conical shape and slenderness of the features as well as periodicity at the nanoscale are all keys to optimising the multi-functionality of the textured surface, but at the same time these demands pose the toughest fabrication challenges. Here we report a systematic approach to concurrent design of optimal structures in the fluidic and optical domains, and a fabrication procedure that achieves the desired aspect ratios and periodicities with few defects, and large pattern area.”
The secret behind the science is that the layers consist of tiny surface features that resemble nanoscale cones — 1,000 times to 100,000 times smaller than the diameter of a human hair.
The technology still needs to undergo further testing but with the coating and etching techniques taken from the semiconductor industry, the commercial potential for wonder glass has been made a reality. Essentially the surface repels not just condensation, but any dirt.
“Our fabricated nanostructures demonstrate structural superhydrophilicity,” the researchers said. Which is an effect discovered in 1995 whereby under light irradiation, water was dropped onto titanium oxide, resulting in a material that could clean and de-fog glass. “Or, in combination with a suitable chemical coating – robust superhydrophobicity.” In short a surface that is difficult to get wet, referred to as the Lotus effect, in regards to the leaves of the plant.
“Enhanced polarization-independent optical transmission exceeding 98% has also been achieved over a broad range of bandwidth and incident angles. These nanotextured surfaces are also robustly anti-fogging or self-cleaning offering potential benefits for applications.”
The innovative glass technology could also be used for optical devices such as microscopes and cameras to avoid moisture problems in hot environments. Also, on touch-screen devices the glass would prevent reflections and issues with sweaty palms.
This is the way that nature works, and may well be the future of greener engineering where two structures and two manufacturing processes are replaced by one
Andrew Parker, a senior visiting research fellow at Oxford University’s Green Templeton College in the U.K. who was not involved in this work, says, “Multifunctional surfaces in animals and plants are common. For the first time, as far as I am aware, this paper learns a lesson in manufacturing efficiency from nature by making an optimized antireflective and anti-fogging device. … This is the way that nature works, and may well be the future of a greener engineering where two structures, and two manufacturing processes, are replaced by one.”
The current manufacturing process is too expensive to produce on a commercial level but when this has been overcome the hope is that the nanotexture technology could revolutionise the manufacturing of glass.