July/August_AMP_Digital

A D V A N C E D M A T E R I A L S & P R O C E S S E S | J U L Y / A U G U S T 2 0 1 8 7 SURFACE ENGINEERING SELF-REGULATING COATING ENABLES SMART WINDOWS Researchers from RMIT University, Australia, developed a new ultra-thin coating that responds to heat and cold, opening the door to smart windows. The self-modifying coating works by au- tomatically accepting more heat during cold temperatures and blocking the sun’s rays when it is hot. The self-regu- lating coating is created by using vana- dium dioxide and is 50 to 150 nm thick. At 67°C, vanadium dioxide transforms from an insulator into a metal, allow- ing the coating to turn into a versatile optoelectronic material controlled by light. The coating stays transparent and clear to the human eye but turns opaque when exposed to infrared solar radiation. Until now, it was impossible to use vanadium dioxide on surfaces of various sizes because coating placement traditionally requires specialized layers or platforms. The researchers developed a way to create and deposit the new coating without the need for these special platforms, so the coating can be directly ap- plied to surfaces like glass win- dows. rmit.edu.au . ULTRA-WHITE COATING MIMICS STRUCTURE OF BEETLE SCALES Researchers from the Uni- versity of Cambridge, U.K., and Aalto University, Finland, developed a super-thin, nontoxic, and edible ul- tra-white coating that could be used to make brighter paints and coatings for the cosmetic, food, and pharmaceu- tical industries. The material, which is 20 times whiter than paper, is made from nontoxic cellulose and achieves such bright whiteness by mimicking the structure of certain beetle scales. Most commercially available white products—such as sun creams, cos- metics, and paints—incorporate highly refractive particles to reflect light effi- ciently. These materials, while consid- ered safe, are not fully sustainable or biocompatible. In nature, the Southeast Asian Cyphochilus beetle produces its ul- tra-white coloring by exploiting the ge- ometry of a dense network of chitin, a molecule also found in mollusk shells, insect exoskeletons, and fungi cell walls. The molecule’s structure scatters light extremely efficiently, resulting in very thin and light ultra-white coatings. Researchers mimicked the structure of chitin with cellulose nanofibrils. By us- ing a combination of nanofibrils with varying diameters, the team was able to tune the opacity and therefore the whiteness of the final material. Mem- branes made from the thinnest fibers are more transparent, while adding me- dium and thick fibers results in a more opaque membrane. In this way, the re- searchers are able to fine-tune the ge- ometry of the nanofibrils to reflect the most light. Like the beetle scales, the cellulose membranes are just a few millionths of a meter thick, although researchers say that even thinner membranes could be produced by further optimizing the fab- rication process. The membranes scat- ter light 20 to 30 times more efficiently than paper and could be used to pro- duce bright, sustainable, and biocom- patible white materials. The technology has been patented by Cambridge Enter- prise. cam.ac.uk , aalto.fi/en. BRIEF CVD Equipment Corp., Central Islip, N.Y., announces that its subsidiary CVD Materials Corp. has entered into an agreement with ME-Metals & Technologies, the Netherlands, to market CVD’s Tantaline anti-corrosion tantalum surface treatment services across the Netherlands, Belgium, Germany, Luxembourg, and Switzerland. cvdequipment.com , me-mt.com . Cyphochilus beetle with cellulose-based coating. Courtesy of Olimpia Onelli. Mohammad Taha displays a vanadiumdioxide coating developed at RMIT.