Ionic liquid–polymer thermochromic electrolytes with a wide and tunable LCST for application in multi-stimuli-responsive optical modulation

Abstract

Multi-stimuli-responsive devices have attracted much attention in the field of smart windows due to their rich color-adjustable effect and high energy efficiency. However, most multi-stimuli-responsive color-adjustable devices have insufficient stability and complex preparation processes, which impede their industrialization. In this work, thermo- and electro-dual-responsive devices were fabricated by preparing thermochromic ion gel electrolytes and combining them with electrochromic films. Locating thermochromic and electrochromic materials in different functional layers reduces their mutual influence and prevents a decline in their single performances. The thermochromic ion gel electrolytes with a lower critical solution temperature (LCST) phenomenon were obtained from a simple UV-curing method with polyurethane acrylate oligomers and ionic liquids. Compared with traditional LCST hydrogels, the ion gels undergo phase transitions without a volume change, exhibit better thermal and ambient stability, and possess a wide electrochemical window. They can be widely used as electrolytes for various electrochromic materials, resulting in color-changing performance and cycling stability comparable to those of organic solution and ionic liquid electrolytes. The ion gels' LCST effect and the electrochromic layers' color-changing characteristics endow the devices with a dual-responsive feature and improved optical modulation ability. This gives the devices great application potential in smart windows and indoor decorations.