As architectural landscapes evolve, so do the windows that frame them. Tomorrow's windows may not just be mere panes of glass, but intelligent entities that dynamically adjust their optical and thermal properties to create a comfortable indoor environment and reduce the energy consumption of buildings.
However, creating materials as building blocks for smart windows that respond to thermal, mechanical and chemical stimuli while meeting aesthetic standards has proven challenging, according to materials science experts.
“In smart windows, the materials must maintain transparency, which narrows down the pool of suitable candidates,” said Yujie Ke, a Scientist at A*STAR’s Institute of Materials Research and Engineering (IMRE).
In their quest for solutions, Ke and Yuwei Hu, a corresponding author of the study, drew inspiration from nature. “We observed how a chameleon changes its colour by altering the crystal structure of its skin, which affects how it reflects light,” Ke said. “Similarly, skeleton flowers change transparency in response to moisture.”
In collaboration with researchers from Nanyang Technological University, Singapore; Beihang University and Beijing Institute of Technology in China; and North Carolina State University, US; Ke and IMRE colleagues developed an innovative film for smart windows. They aimed for a design capable of tri-mode stimuli response, integrating thermochromism (sensitivity to temperature changes), mechanochromism (reactivity to mechanical stress), and hydro-/solvato-chromism (responsiveness to water or solvent contact).
Design of a novel window film capable of changing transparencies and colours based on heat, light and mechanical forces. Comprised of silica (SiO2) nanospheres, vanadium dioxide (VO2) and polydimethylsiloxane (PDMS), its structure was based on the colour-shifting nanocrystal lattices found in chameleon skins, as well as the intercellular spacing in skeleton flowers which change transparencies for dry and wet weather conditions.
Leveraging a bio-inspired hierarchical structure and functional elastomers, they engineered a composite of vanadium dioxide and polydimethylsiloxane, layered over silica nanospheres. “These nanospheres introduce structural changes when stretched, enhancing light scattering, while the vanadium dioxide particles react to temperature, modulating light transmission,” Ke said.
When incorporated into smart windows, the film can optimise a building's energy consumption by dynamically manipulating how light enters it. This would substantially reduce its reliance on heating and cooling systems, lowering overall energy expenses.
Moreover, this technology paves the way for customisable aesthetics. “Our method allows for the dynamic control of colours and patterns, adding an element of design flexibility that was previously unexplored in smart windows,” said Ke.
In simulations, the team’s smart windows outperformed the energy efficiency of conventional single-layered and double-glazed windows in cities like Barcelona, Melbourne and Auckland. Nevertheless, scaling up production might present a hurdle to widespread adoption, particularly for developers aiming for cost-effective solutions with rapid payback periods.
To meet market demands, the team has plans to improve the solar management performance of their smart windows, for which they have filed a provisional patent. By integrating features such as on-demand privacy and aesthetic enhancements, they aim to elevate the smart window design’s value and expedite the payback period.
The A*STAR-affiliated researchers contributing to this research are from the Institute of Materials Research and Engineering (IMRE).
