Forget curtains, switch to smart windows

Windows made of hydrogel change from transparent to opaque when heated

Published - November 11, 2017 07:35 pm IST

  Heat-sensitive  Hydrogel window on the right is warmed and so has turned opaque.

Heat-sensitive Hydrogel window on the right is warmed and so has turned opaque.

Scientists at Bengaluru have developed a smart window that automatically turns from transparent to opaque when heated and also gets back to its original transparent state when the heat is removed. These windows can potentially be used in homes, offices, and even cars and aeroplanes.

Researchers at the Centre for Nano and Soft Matter Sciences (CeNS) have come up with three different types of windows (thermochromic, hydrocarbon, hydrogel) with different behaviours. Windows made of hydrogel change from transparent to opaque when heated and back to transparent when heat is removed. Thermochromic and hydrocarbon windows are opaque at room temperature and become translucent and transparent respectively when heated.

Solar and electronic controls

Basic component of these optoelectronic devices (electronic devices that operate on both light and electrical currents) is the transparent heater. Thermochromic windows have an ordinary glass-based transparent heater coated with commercially available temperature-sensitive pigments. This allows it to turn from opaque to translucent when heated “This window can be used in cold winter regions, when you want the sun to warm up your room through passive smart window. By supplying very small (0.2 watts/cm2) current the transparency of the window can be changed according to your needs,” explains Dr. Giridhar U. Kulkarni, Director at CeNS and corresponding author of the paper published in the Journal of Materials Chemistry C.

The second and third type windows were fabricated by filling in either hydrocarbon (commonly available fatty acid) or a hydrogel (hydroxypropyl methyl cellulose) between a glass mounted with transparent heater and a plain glass.

“The hydrogel window is ideal for our Indian offices and homes. When the temperature reaches around 40 degree C, the glass turns opaque providing an efficient heat management system for offices with large windows. The windows can be also be controlled by providing just 0.2 watts/cm2 and it takes just two minutes to turn completely opaque,” says S. Kiruthika, co-author of the work from Jawaharlal Nehru Centre for Advanced Scientific Research (JNCASR), Bengaluru.

The hydrogel windows can restrict infrared radiation thus reducing the indoor temperature. The researchers found that the temperature in an experimental control area with hydrogel window was nearly 10 degree C lesser than plain glass windows.

“All three types of windows are very cheap costing less than Rs.100 per sq foot. These can be installed to create less energy-consuming buildings,” says Ashutosh K Singh, Research Associate, CeNS and first author of the paper.

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