Thermotropic effects are characterized by the transition from a clear to a light scattering state. Cause of light scattering are domains whose refractive index differs from that of the surrounding matrix. In the development of thermotropic materials extensive experience is available at Fraunhofer IAP.

Thermotropic polymers

Regulation of transparency − Thermotropic polymers


Thermotropic polymers autonomously switch from a clear to a scattering state when the temperature rises. No external power is required for this process. They are therefore suitable for applications in the sun, glare and overheating protection as well as in light control.

These new materials reduce the energy consumption of buildings. In winter, the solar heat reduces heating energy requirements. In summer, a large portion of the solar radiation is reflected, thus reducing the cost of cooling and ventilation.

Focus of our material development is the transformation of thermotropic effects in polymer matrices - self-supporting thermoplastic films and wall sheets, as well as resins and hydrogels for laminated glass.

Thermotropic resins − SOLARDIM®-ECO


SOLARDIM®-ECO – self-regulating solar protection glazing

Transparent cast resins are used multifariously for producing laminated glass for windows in structural engineering and vehicle manufacturing applications, façade panels and roof glazing.  Combining them with thermotropic properties enables more high-performance solar protection.

Specially developed pigments are added to the cast resins to produce thermotropic laminated glass. Because the elements of cast resin are usually highly reactive, the pigments must have a high chemical stability. The thermotropic cast resins reflect the solar rays. The intensity of the cloudiness and the switching temperature can be adjusted. The laminated windows have long-term stability and do not need maintenance.

Thermotropic hydrogels


Transparency changes (Thermotropy) are either based on the appearance of lyotropic liquid crystalline phases or on the occurrence of phase separation processes, whose switching temperatures can be adjusted by varying the hydrophilic-hydrophobic-balance of the polymer material. The outstanding feature of thermotropic hydrogels is their high transparency in the clear state.

Transparency and color changes (Thermochromism) can be combined in one material, whereby the switching temperatures can be adjusted independently. Our long-term experiences in this field enable us to design hydrogels with customized thermotropic and/or thermochromic properties. The outstanding optical properties of hydrogels make these materials promising for the use in hybrid light and heat regulating sun protection glazing. Prototypes of such smart glazing with an area of up to 1m 2 are currently tested under practical conditions.

Thermotropic window

Transparent thermoplastics such as polyolefins, polycarbonates and polymethacrylates are linear, non-crosslinked polymers. Most thermoplastics can melt without degrading and therefore can be processed into films and multiwall sheets using extruder technology. During processing the raw materials are subjected to high thermal and mechanical stress. Our pigments can be added before the extrusion process and enable a technology-compatible production of thermotropic films for the first time.

They can be applied in greenhouse construction, as agricultural films, in solar collectors and in roof construction.