Humidity Responsive Reflection Grating Made by Ultrafast Nanoimprinting of a Hydrogel Thin Film

The response time of state of the art humidity sensors is approximately 8 s. A faster tracking of humidity change is especially required for health care devices. We focused our research on the direct nanostructuring of a humidity-sensitive polymer thin film and combined it with an optical read-out method. Our goal was to improve the response time by changing the surface-to-volume ratio of the thin film and to test a different measurement method compared to state of the art sensors. Large and homogeneous nanostructured areas were fabricated by nanoimprint lithography on poly(2-hydroxyethyl methacrylate) thin films. Those thin films were made by initiated chemical vapor deposition (iCVD). To the author's knowledge, this is the first time nanoimprint lithography was applied on iCVD polymer thin films. With the imprinting process we developed a diffraction grating in the visible wavelength regime. The optical and physicochemical behavior of the nanostructures was modeled with multi-physic simulations. After successful modeling and fabrication a first proof of concept showed that humidity dependency by using an optical detection of the first diffraction order peak is observable. The response time of the structured thin film resulted to be at least three times faster compared to commercial sensors. This article is protected by copyright. All rights reserved.