Chemists at Ludwig-Maximilians-Univeristaet (LMU) in Munich have fabricated a novel nanosheet-based photonic crystal that changes color in response to moisture. This new material could form the basis for humidity-sensitive contactless control of interactive screens on digital devices.
LMU chemists developed their photonic crystal from ultrathin nanosheets of phosphatoantimonic acid, which are extremely sensitive to moisture. “These photonic nanostructures change color in response to variations in local humidity,” says Bettina Lotsch of the Department of Chemistry at LMU and the Max Planck Institute for Solid State Research in Stuttgart. “This makes them ideal candidates for the development of novel user interfaces for touchless devices.” This new sensing platform is described in Advanced Materials.
“The humidity around a fingertip is slightly higher than the overall level of moisture in the ambient air,” explains Katalin Szendrei, a member of Lotsch’s research group. “This difference can be detected by our photonic sensor, and causes it to change color – without any contact with the nearby fingertip.” It is this extreme sensitivity to local moisture that makes the nanostructure so interesting for use in ‘touchless’ screens.
"The humidity around a fingertip is slightly higher than the overall level of moisture in the ambient air. This difference can be detected by our photonic sensor, and causes it to change color – without any contact with the nearby fingertip."Katalin Szendrei, Ludwig-Maximilians-Univeristaet
“Contactless control is a particularly attractive option for next-generation positioning interfaces such as ticket machines or cash dispensers, which are used by hundreds of customers each day. In this case, touchless navigation has obvious advantages with respect to hygiene,” says Szendrei.
Photonic crystals are periodically arranged nanostructures that possess the ability to reflect, guide and confine light. They are also found in the biological world, where examples include mother-of-pearl and the iridescent wing-scales of certain butterflies, such as the shimmering Morpho butterflies of the Amazon Basin.
When developing their photonic crystals, Lotsch and her team turned to phosphatoantimonic acid because it is extremely moisture sensitive but also chemically stable, transparent and easy to fabricate into nanosheets. In comparison to other nanosheet-based vapor sensors, the new photonic architecture displays markedly increased response times, higher sensitivity and long-term stability. “This unique combination of properties enables it to track and color-code finger movements in real time,” says Pirmin Ganter, who also works in Lotsch’s group. In addition, the new system is also stable on exposure to air, and therefore functions not just under controlled conditions in the laboratory but also in the constantly varying environment of the real world.
Lotsch and her collaborators have already applied for patent protection for the novel device. Together with the Fraunhofer EMFT in Munich, they are now working on a prototype screen that, in addition to providing color-coding, will also be equipped with an electronic readout capability.
This story is adapted from material from Ludwig-Maximilians-Univeristaet, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.