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Thermotropic layers for light transmission switching

: Wilson, H.R.; Eck, W.

Jesch, L.F. ; European Commission:
TI6. Sixth International Meeting on Transparent Insulation Technology. Proceedings
Birmingham: Franklin Company Consultants, 1993
ISBN: 0-9510781-7-8
International Meeting on Transparent Insulation Technology <6, 1993, Birmingham>
Fraunhofer ISE ()

Thermotropic layers, which are characterised by a variable light transmittance depending on the temperature, have been developed to provide an alternative to mechanical systems for shading TI elements to prevent overheating. The type of layer investigated consists of a cross-linked polymer blend, which changes reversibly from a transparent to a light-scattering state when it is heated. It can be applied as a thin film onto a glass pane, and causes only a slight reduction (about 2 %) in the light transmittance in its clear state. Above the switching temperature, the direct-hemispherical trasmittance is decreased due to backward light scattering by 50 % or more, depending on the thickness of the layer, which is typically between 300 Mym and 1 mm. The switching temperature itself depends on the chemical composition of the blend and has been varied between 30 degrees C and 100 degrees C in the investigated samples. The paper presents the range of switching behaviour (light transmittance vs temperature) which has been achieved, results from long-term stability tests, approaches for large-area production and the predicted effect of the light transmission control on complete TI systems, obtained with computer simulation.