Automatically Modulated Thermoresponsive Film Based on a Phase-Changing Copolymer

Thermoresponsive materials, in particular those exhibiting switchable optical transmittance via temperature change, have been widely used in different applications. If the required temperature change is within seasonal temperature changes, the transmittance change would consume low energy or be autonomous. Here, a solid-state thermoresponsive phase-changing copolymer (TPCC) film has been demonstrated, with a large transmittance modulation between room and hot temperatures (>28 °C). The polymer film comprises a hydrophilic poly(hydroxyethyl acrylate) (HEA) cross-linked with a hydrophobic phase-changing poly(hexadecyl acrylate-co-tetradecyl acrylate) (HDA-TA). The TPCC was designed such that the HEA and HDA-TA moieties produce micrometer-scale phase separation, the HDA-TA moiety undergoes reversible crystalline-to-amorphous transition at 28–32 °C, and the refractive indices of the hydrophilic and hydrophobic phases are matched at ambient temperature but are mismatched when the temperature is above the transition. The TPCC film showed high modulations of transmittance in the visible (390–780 nm), solar (300–2500 nm), and infrared (780–2500 nm) spectrum of 68.8, 62.7, and 55.8%, respectively. The opacity switching was reversible without any decay after 1000 heating–cooling cycles. The TPCC film was investigated for autonomous and climate-adaptable solar modulation window application.