Plastic sheets being UV-cured in a UV-curing machine

How many times have you squirmed at the early morning sun rays and buried your head back in the pillow or taken pains to get up and draw the curtains?

In the hi-tech era of remote-controlled window light adjustment, you need not do that anymore. Scientists at the Central Glass and Ceramic Research Institute in Calcutta (CGCRI) have come up with technology that can adjust the amount of light flooding into your room by altering the colour of the glasses used in the windowpanes with the use of Electro Chromatic Devices (ECDs).

Dr Prasanta Kumar Biswas at the premier CSIR lab’s sol-gel division and his team have found a unique way of coating float glass (normal glass used in windowpanes) with transparent conducting oxides (TCO) like indium tin oxide (ITO) or fluorine doped tin oxide (FTO).

“The purpose of coating normal glass sheets with these oxides is to impart a metallic character to the sheets. This enhances the heat reflecting character of the glass, thereby limiting the amount of heat radiation entering the room,” Dr Biswas said.

Solar radiation that reaches the earth gets absorbed and a radiant energy is emitted in the form of radiation but at a different wavelength. That is why heat rays passing through glass panes cannot leave the room as their wavelengths change. Hence the temperature of a greenhouse is higher than that of normal homes. But the CGCRI team has altered this theory by tinkering with the wavelength of the light coming in.

The fluorine-doped glass sheets were made by a technical procedure called online high volume production through chemical vapour deposition, where the sheets were introduced into a chamber containing ITO or FTO vapours. This in turn deposit on the glass surface to form a thin film of TCOs. This special glass, currently imported from China, costs about $ 250 per square feet. But if the researchers at CGCRI manage to get a patent for this innovation, the glass will hit the Indian market at a significantly lower price soon.

“Ours is an R&D lab; we can’t only market products. A joint effort of our lab, the government and industrialists is needed to make the product reach the masses at low cost,” said Dr Biswas.

These coated glass pieces can also be used as transparent electrodes in calculators. Their ability to conduct electricity and alter colour depending upon the amount of current they conduct further widens its application in Electro Chromic Devices (ECDs). Hence by connecting the glass panes to the electrical devices, one can actually control the amount of heat and light entering the room.

Another team at the institute led by Dr Gautam De has obtained a patent for an innovation that makes plastic surfaces of much used items like cellphones and computer screens scratch-resistant.

The process involves a unique way of coating the transparent plastic surface with polyethylene oxide and nanoparticles. The plastics are layered with sol-gel, followed by thermal ultra-violet curing, where sheets of coated plastic are passed over conveyor belts to be treated with ultra violet rays. These hard-coatings are transparent and spot free. “These coatings not only make the glasses scratch resistant but also impart an anti-reflective character to the glass surface. The coatings are capable of reflecting different coloured light rays from the visible spectrum, which can be tuned as per the customer’s choice,” said Dr De.

With glasses being increasingly replaced by plastic in ophthalmic lenses (used in telescopes, microscopes and spectacles), this innovation comes as a relief to many. “Constant scratching of the optical surface makes the ophthalmic lenses or the plastic surfaces used in windowpanes lose their transparency and hence visibility,” he added.

The innovation also means good news for the railways, which spends crores of rupees in replacing scratched panes of coaches every year. The technique involved here is the same as that used in tinting glass sheets.