Ultra-large and Multi-stimuli-responsive Smart Windows

According to a recent article in Nature News & Views (2019), optical modulation technologies that can self-respond to the surrounding environment with minimal energy consumption could have a tremendous impact in many areas of our lives. Self-responding optical modulation technologies based on mechano- and thermochromic materials have been considered a powerful approach for realizing a next-generation smart membrane. To that end, Prof. Kim and Prof. Jeon’s groups at KAIST has taken a major step toward developing a new class of multi-stimuli-responsive (mechano- and thermochromic) membranes which can be produced over an exceptional large scale (over 300 cm²). A rational design for the mass production of customized nanofibers was realized through coupling the focused electric-field polymer writing (FEPW) technique with the roll-to-roll technique. The study was published in September on ACS Nano, a highly-cited research journal (Focused Electric-Field Polymer Writing: Toward Ultra-large, Multi-Stimuli-Responsive Membranes, ACS Nano, 2020).

“High uniformity over the whole active area and scalability beyond the wafer level are issues that crucially affect the transition into practical applications such as smart windows in energy-zero buildings” according to a statement by Prof. Kim and Jeon.

The research groups of Prof. Il-Doo Kim, Prof. Hong Jung-Wuk, and Prof. Seokwoo Jeon solve these issues by employing a new class of multi-stimuli-responsive membranes (exhibiting mechano- and thermochromism) that can be fabricated in an ultra-large area via FEPW. The fabrication strategy and the collective set of results represent state-of-the-art direct writing technology for the on-demand mass production of nanofiber building blocks. In addition to the advantages of current 3D writing technologies, the high degree of freedom to additionally integrate different functional materials in a one-pot process brings several rather notable benefits. These features enable the optimization of the governing form factors of the optical modulating membrane, leading to promising opportunities to construct a multi-stimuli-responsive membrane (with mechano- and thermochromism). Due to its improved uniformity and geometry-dictated functions, two-phase mechanical and optical simulations were carried out to carefully verify the underlying multiphysics, which is the light scattering at the interfaces of the strain-induced air gaps. Further improvements in optical modulation rely on control of the distance between the adjacent nanofibers of the membrane within hundreds of nanometers, leading to increase in the optical density. Finally, the combination of the FEPW technique with roll-to-roll production empowers the successful expansion of the production area of the smart membrane to an exceptionally large scale of up to near 300 cm², beyond those of previously reported optical modulating membranes to date. Overall, the concept of the rational one-pot method presented in this work holds great promise as a new structural platform technology for optical as well as electrochemical applications with on-demand designs and properties.