Abstract
To maintain the temperature of heated or cooled air inside a room, one needs to put thermal insulation on the transparent glass windows where heat most frequently comes and goes. Fibrous materials and gas-foamed plastics provide some insulation due to the low thermal conductivity of air but are not transparent. Here we show that a nano-spaced polymer film consisting of hollow silica nanoparticles dispersed in a polyurethane matrix provides good thermal insulation and is transparent. One advantage of using hollow particles is that a quasi-vacuum state in the nano-space is formed when the size of the space is close to the length of the mean free path of the air molecules in the space. Heat tends to be transferred along the silica shells of hollow particles instead of through other materials in the film. To depress flocculation of the hollow particle in the film is the key to both transparency and good thermal insulation.
