Thermochromic smart windows with broad-range customizable responsive temperature via the Hofmeister effect

Abstract

Thermochromic smart windows exhibit intelligent building energy conservation once the ambient temperature is higher than their responsive temperature (T_r). However, most current smart windows regulate the light at an invariable T_r, which fails to meet the T_r requirements of various inhabitants in diverse climate conditions. Herein, we propose a novel T_r customization stratagem for thermochromic smart windows by tuning the low critical solution temperature of PNIPAM-derived thermally responsive materials (TRMs) via the Hofmeister effect. Density functional theory (DFT) calculations and molecular dynamics (MD) simulations successfully verify that the T_r is highly related to the number of hydrogen bonds and the interaction energy between TRMs and H₂O and salts with the Hofmeister effect can effectively manipulate the hydrogen bonds and hydration structure around polymer chains. Therefore, specific salts can be introduced into the thermochromic system to adjust the T_r over a broad range by changing the type and concentration of salts. Additionally, a polynomial expression relating the concentration of salts and the T_r can be established to up/down customize the T_r of the corresponding smart windows predictably. This stratagem provides a cost-effective avenue for the popularization of thermochromic smart windows in different climate conditions together with remarkable optical modulation and building energy conservation (e.g., 128.4 MJ m⁻² in Hong Kong), which is very helpful for accelerating the global low-carbon economy for sustainability.