From Thermochromic Phenomena in Polymers

Another way to obtain thermochromic polymers is to incorporate a thermochromic material into a polymer matrix. Both components build separate phases and do not influence the phase structure of the other component. Microencapsulated leuco dye-developer-solvent systems, inorganic pigments and conjugated polymers are suitable candidates for this purpose. Leuco dye-developer complexes are by far the most important systems to achieve thermochromic properties for different polymer materials by realising a separate phase of the thermochromic system in a non- thermochromic polymer matrix. With regard to their importance for the development of thermochromic materials the properties of these complexes are discussed in much more detail than those of inorganic thermochromic pigments or thermochromic conjugated polymers.

3.1 Leuco Dye-Developer-Solvent Systems

Leuco dye-developer-solvent systems consist of an electron- donating chromogenic compound (leuco dye), an electron acceptor (developer) and a matrix component (solvent) [1]. The most common electron-donating chromogenic compounds are phenylmethane and fluoran derivatives bearing a lactone ring moiety. In the lactone ring-closed state these so-called leuco dyes or colour formers [2] are either colourless or weakly yellow coloured. On reaction with an electron-accepting developer an opening of the lactone ring occurs resulting in the formation of a zwitterionic structure. As a result of this reaction the conjugated ?-electron system of the dye is extended and the longest wavelength absorption peak shifts from the UV to the visible range. Thus the dye becomes coloured. The addition of an appropriate solvent component enables the colour-forming reaction to be reversible with temperature. Leuco dye-developer-solvent systems are...

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Topics of Interest

3.2 Inorganic Pigments In contrast to the thermochromic effect of organic composites, thermochromism of inorganic materials, such as metal salts and metal oxides, has been well known for a long time...

3.6 Applications Thermosensitive recording paper was launched onto the market by the National Cash Register Company in 1968. It consists of a paper sheet coated with a single thermosensitive layer...

Overview Chromogenic polymers change their visible optical properties in response to an external stimulus [1]. In terms of the specific stimulus they are subclassified as thermochromic (temperature),...

The intention of the project was to evaluate aesthetic and technical performance of thermochromic dyes in conjunction with integrated heating mechanisms. Thermochromic dyes change color with...

3.4 Comparison Between the Three Different Classes of Thermochromic Additives A comparison between the classes of thermochromic additives presented in Sections 3.1 3.3 is given in Table 3.2. The...