Reduction of solar infrared heating by using highly transparent thin films based on organic chiral nematic liquid crystal polymer

This paper demonstrates a thin and transparent reflector film for the near infrared, based on chiral nematic liquid crystal (CLC) polymers. Two films reflect almost 50% of unpolarized incident light from 730 to 820 nm and from 880 to 1030 nm, while remaining completely transparent in the visible region with transmittance >90%. An efficient window uses the combination of two reflectors. After exposing two window-cubes for 2 h to direct sunlight, the temperature inside the cube with reflector windows was 4μClower than in cube with plain windows. This reveals that the infrared (IR) reflectors can effectively control the indoor temperature. These films, which are 8μmin thickness, can be detached from the glass substrates and used as a free-standing film, or be attached to a flexible optical foil or a solid window. The foils can be applied in buildings, offices, and automobiles to statically reduce the energy consumption required for air conditioning or lighting. The free-standing foils show acceptable resistance to polar protic solvents and are thermally stable up to 100μC.