Mineralized supramolecular hydrogel as thermo-responsive smart window

Everlasting pursuit of the high energy efficiency as well as meeting fluctuant temperature causes various lighting requirements over the day, which is driving the demand for creating a multifunctional smart window (SW) system. Here, an upper critical solution temperature (UCST)- and/or lower critical solution temperature (LCST)-type SW system (denoted as SWU, SWL and SWU+L, respectively) was fabricated through a simple bio-inspired physical cross-link process between amorphous CaCO3 (ACC) and poly(acrylic acid) (PAA). Series of mineralized hydrogel-based chromic layers were first in situ formed by sealing the composite of ACC in PAA matrix into polyethylene terephthalate (PET) “sandwich structure” to fabricate the SW system. As expected, the SWU system exhibited a typical UCST transition process, bringing about a luminous transmittance (Tlum) of 40.70% at 25 °C and a Tlum of 74.76% at 45 °C. The high scattering of the initial state as well as large optical contrast (ΔTlum $$=$$ 34.06%) of the SWU system guarantees residential privacy and energy savings. Also, a thermochromic SWL system with a relatively high luminous transmittance (Tlum) of 47.81% at 25 °C and an acceptable solar modulation property (ΔTlum $$=$$ 16.06%) was constructed. A conceptual SWU+L system was fabricated, that is, a sharp UCST transition followed by a LCST process. This reversible two-stage optical switch process subsequently occurs by continuously increasing temperature, endowing this SW system highly suitable for SW or logic gate. The SW system with multi-thermo-responsiveness brings more flexibility in building facade design.