The researchers printed a plastic sheet on a 3D printer with a surface relief that allows it to reflect most of the incident light, while the print material is selected so that its refractive index was identical to the same indicator in methyl salicylate exists. It is widely used in medicine and cheap to manufacture.
Then the engineers took a panel of ordinary glass and fastened a plastic sheet on it, leaving a tiny gap between them. While it is empty, light passing through the glass is reflected back, but it is worth pumping a little methyl salicylate into the cavity, as the reflection coefficient drops almost to zero and the entire design becomes virtually transparent. If you install a simple light sensor and a microcontroller to control the pump, you can get an automatic glass transparency switching system.
The liquid circulates in the system and is not an expendable material, the prototype of “smart glass” has already withstood tens of thousands of work cycles without node degradation. Yes, we need a source of energy for the pump and some time for pumping methylsalicylate, but from the engineering point of view this system is easy to adapt for any conditions. Plus, another advantage – since light is reflected and not absorbed, as in the case of car glass tinting, such a glass does not heat up.