Thermotropic Polymer Gels: Smart Gel Glass

Several attempts have been made recently in order to develop smart windows, which can moderate light and heat intensities. Thermotropic gels have met with growing interest because of their advanced properties. Based upon phase transitions of polymer gels, a novel thermally adjustable window, which includes a gel layer, has been developed in our laboratory. The so-called gel-glass becomes opaque when the temperature exceeds a certain value and goes back to its original transparent state when it is cooled below the critical value again. Intelligent gel-glasses made of these materials can moderate the amount of sunlight and radiated heat. The optical properties of the gel layer are also modified by the Joule heat of audio frequency AC current. Two types of gel-glasses have been developed and investigated. Phase transition temperature of a poly(N-isopropylacrylamide) based gel was adjusted by copolymerization and by changing of the solvent composition. The cloud point of a poly(methyl vinyl ether) - water system in a PVA gel was varied by modifying the composition of the swelling agent. In the case of electrically adjustable thermotropic windows, optical properties, energy consumption and temperature changes during the switching process were studied.