Bidirectional Thermoresponsive Window via a Facilely Tailorable Double-Layer Hydrogel.

Area of Science:

• Materials Science
• Polymer Chemistry
• Sustainable Energy

Background:

• Smart windows offer dynamic transmittance control for energy efficiency and comfort.
• Traditional smart windows struggle to balance energy-saving and privacy functions due to challenges in controlling phase transition temperatures.
• Tailoring smart windows for specific applications is limited by the precise control of their thermal-responsive properties.

Purpose of the Study:

• To develop a novel double-layer hydrogel (DHG) smart window with independently tunable lower critical solution temperature (LCST) and upper critical solution temperature (UCST) layers.
• To achieve simultaneous energy-saving and privacy functions by precisely controlling the phase transition temperatures of the smart window.
• To enhance the customization and processing of smart windows for diverse application scenarios.

Main Methods:

• Fabrication of a DHG smart window by integrating a cellulose-based LCST hydrogel layer and an acrylamide/acrylic acid (AM/AA) copolymer UCST hydrogel layer.
• Independent tuning of LCST (23.1-34.2 °C) via molar substitution degree of cellulose derivative and UCST (1.0-16.2 °C) via AM/AA molar ratio.
• Evaluation of optical properties, including visible light transmission (Tlum) and solar modulation (ΔTsol), and thermal insulation performance.

Main Results:

• The DHG smart window demonstrated excellent visible light transmission (Tlum = 82.14%) and significant solar modulation (ΔTsol,LCST = 76.60%; ΔTsol,UCST = 75.28%).
• The smart window effectively transmitted light within a comfort temperature range, blocked solar radiation at higher temperatures for thermal insulation, and provided privacy at low nighttime temperatures.
• Precise and independent tuning of LCST and UCST was achieved, allowing for tailored performance based on environmental conditions.

Conclusions:

• The developed DHG smart window successfully integrates energy-saving and privacy functions through precisely controllable and independent phase transition temperatures.
• The DHG smart window offers superior thermal insulation compared to traditional windows and satisfies indoor illumination requirements.
• The precisely tunable nature of the DHG smart window makes it highly suitable for intelligent temperature monitoring and various customized applications.