From water and hydrogel: created an energy-saving smart window

Scientists have created a smart window that becomes impermeable when heated. In summer, such a window will prevent the room from overheating. The window consists of a liquid mixture of water and hydrogel, enclosed between layers of glass. The study is published in the journal Joule. What is known Scientists have developed heat-sensitive polymers that respond to changes in temperature. The lower critical temperature is 32 degrees Celsius. This temperature determines the transition from hydrophilic to hydrophobic properties of the material. Below, its polymer mixes with water and the solution becomes transparent, and when heated it becomes hydrophobic and gives off water – visually the solution becomes cloudy and worse transmits sunlight. A team of scientists led by Yang Zhou from Nanyang Technological University noticed that water can store heat better than other common building materials, such as wood, metal and concrete. They used this property to design a smart window. The window itself is a mixture of polymer particles (N-isopropylacrylamide) and a large amount of water, which is poured between two glass scarves. The solution is free-flowing, so it does not require complex application procedures. The window works due to two mechanisms: changes in transparency and heat accumulation. Smart window at different times of the day and season, where yellow arrows indicate visible light, and red – heat / Photo Yang Zhou et al

At low temperatures outside, the window is transparent and transmits light. When heated by sunlight, the phase transition of the polymer is started and the window becomes cloudy, first it becomes translucent and then opaque. Heat from sunlight is absorbed by the solution. Scientists conducted tests, 100 times heating the window to 60 degrees Celsius and cooling to 20 degrees. The researchers estimated that such a window will last 17.6 years – at least a year and a half longer than other smart windows. In addition, a window with a layer of solution one centimeter thick reduces the noise level well. The sound insulation index in the tests was higher than that of double glazing.