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.