Thermochromic Ionogel: A New Class of Stimuli Responsive Materials with Super Cyclic Stability for Solar Modulation

In this work, a new class of polyurethane based ionogels that can respond to external stimulus, e.g., temperature, has been synthesized. The ionogels are mechanically robust and undergo an LCST-type phase transition with no volume change upon heating accompanied by a switching of optical transmittance. The optical switching temperature is tunable within a wide range between subzero to over 100 °C. Molecular dynamic simulation aided molecular design and provided further mechanistic understanding. Apart from the LCST-type transition, these ionogels are absent of freezing point and volatility and demonstrated unprecedented superhigh optical cyclic stability even after 5000 heating-cooling cycles with no detectable liquid leaching. In addition, these ionogels are chemically compatible with a range of additives such as organic dyes and photothermal plasmonic conducting nanoparticles which endow multifunctionality and versatility in terms of applications. A model mini-house affixed with the ionogel-incorporated glazing demonstrates a reduction of indoor temperature by up to 20 °C far superior to state-of-the-art tungstate coated glazing. This new class of ionogels marks an important milestone in smart materials development for a range of applications including autonomous and climate-adaptable solar modulation window.