Today, 19 February 2015, is the start of Chinese New Year – the year of the goat. However, the Chinese ‘New Year’ is only described as such in the West; in China, it is the Spring Festival and an official public holiday.
Traditionally, today is an important time of year for families to spend together.So I thought I would bring our chemical engineering family a little closer together by sharing a good news story from some of our colleagues in China.
Chemical engineers from the East China University of Science and Technology, Shanghai Institute of Ceramics, Shanghai University, Shanghai University of Engineering Science and Shihezi University have worked together to develop energy saving ‘smart’ windows that exploit the properties of a heat sensitive gel.
Controlling the temperature of buildings is a tricky business; sunlight streams through windows, which can heat up a room. In winter, it would be useful to be able to harness this heating power, but in the summer the additional solar heat gain is often problematic and tackled using air conditioning.
We can limit this effect ourselves by drawing blinds or curtains. However, consider a situation where the transparency of the windows could change according to the external temperature. The smart windows developed through this research can do just that.
There are already some smart windows on the market which work using LCD (liquid crystal diode) technology – when an electric current flows through the window, the coating on the pane of glass darkens, thereby blocking out some of the light. However, this type of smart window is dependent on a external power source.
The Chinese team’s smart window research, led by Xuhong Guo, a chemical engineer from the East China University of Science and Technology, does not require any electricity and is controlled by the external temperature.
Xuhong’s group have designed a new colloid that, when sandwiched between two panes of glass, acts as a smart window. This research was recently published in a paper in the journal, Industrial & Engineering Chemistry Research: Binary Solvent Colloids of Thermosensitive Poly(N-isopropylacrylamide) Microgel for Smart Windows.
A colloid is a substance in which insoluble particles are spread/suspended throughout the larger volume of another substance – a good everyday example of a colloid is milk, which has tiny amounts of butterfat suspended throughout its liquid.
In Xuhong’s work, the colloid suspends a heat sensitive polymer (poly(N-isopropylacrylamide)) which forms aggregations between 200-700 nanometres in size, to make this microgel. The polymer changes shape whenever its temperature rises above 32°C.
At low temperatures, the polymer remains long and straight and as it is able to dissolve throughout the microgel, this allows light to pass through – making it appear clear.
As the microgel’s temperature rises above 32°C, the polymer coils into small balls that can’t dissolve in the microgel – making it appear cloudy and thus obstructing some of the sunlight.
The new smart window blocks about 25 per cent of visible light and infrared energy emitted by a sun lamp, reducing the temperature by 20°C, compared with just 10°C by a standard window.
The microgel colloids used in this research show a short response time, low freezing point and good energy-saving performance, which make them an excellent candidate for applications in smart windows.
I would also like to say Happy Chinese New Year (or Spring Festival) to all my blog readers, no matter where they are based in the world. Enjoy your celebrations and may the Year of the Goat bring you much luck and happiness.