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Evaporation is crucial in many applications. One of the critical parameters affecting evaporation is surface wettability, which is often tailored using coatings and micro- or nanoscale features on the surface. While this approach has advanced many technologies, the ability to control wettability dynamically can add new functionalities and capabilities that were not possible before. This study demonstrates how a self-cleaning superhydrophobic surface with an equilibrium contact angle of 155° can dynamically change to a superhydrophilic surface with a contact angle near 0°, resulting in drastically different evaporation characteristics. Specifically, we find that the evaporation rate and surface temperature reduction due to the resulting cooling are 3 times higher due to the change in surface wettability. This change in wetting behavior is due to the use of an amino-silane [N-(2-aminoethyl)-11-aminoundecyltrimethoxysilane]-functionalized surface, which is altered in the presence of dilute acetic acid. Upon complete evaporation, the surface reverts to superhydrophobic behavior. This reversible behavior is not seen in traditional nonwetting coatings like perfluorodecyltrichlorosilane and lauric acid. This strategy for dynamic control of wettability and evaporation can lead to advancements in many applications ranging from self-assembly-based fabrication processes to oil–water separation and advanced thermal management technologies. 

Abstract Smart windows have the potential to respond dynamically and passively to external stimuli, controlling the amount of light passing through the window. When a smart window switches from a clear to a translucent state, energy flow through the window is partially attenuated, allowing a room to cool down passively, thereby reducing the energy and fossil fuel consumption for air conditioning. The smart window demonstrated here consists of a thermoresponsive liquid consisting of Tergitol 15‐S‐7, which can dynamically and passively switch the window's transmittance when a temperature of 39 °C is reached. It is also demonstrated how the transition temperature can be lowered by adding salts. Outdoor experiments in realistic environments show that the temperature of a model house built with a thermo‐responsive window can achieve an indoor temperature of 7 °C less than a control house with an ordinary window. This study quantifies the energy savings possible using such windows at the building scale for cooling and heating in different climates and times of the year.