Color switching, electrically controllable

Figure 6.10 Light transmission spectra of 5 p.m DHF-FLC cell placed between two crossed polarizers versus applied voltage at a frequency of color switch of 100 Hz the horizontal size of the micrographs is 500 p.m [19]. Reproduced from E. P. Pozhidaev, G. Hegde, P. Xu, and V. G. Chigrinov, Electrically controlled birefringent colors of smectic C deformed helix ferroelectric liquid crystal cells. FLC 07 Program, FLC International Conference on Ferroelectric Liquid Crystals, 0-36 (2007)...

Conjugated polymers are very significant, smart, or responsive materials. Indeed, many properties (color, conductivity, volume, hydrophiHcity, permeability, etc.) depend on their oxidation state and can thus be reversibly controlled by the potential applied to the material. As an example, smart windows [2] are based on the electrochromism of these coatings, that is, the ability to switch these polymers reversibly between dark and colorless state by simple control of the polymer redox state. The intensity of Hght transmission through a window incorporating such a layer can thus be tuned at will by external electrical stimuli. 

A polymer gel based on an (inverse) opal was applied in order to obtain shorter switching times, which are also desirable for electrochemical color display purposes [346]. Hence, an all-color display was developed that, dependent on the applied potential, could reversibly switch between blue, green, red, and black. Here, crosslinked polyferrocenylsilane gels were partly swollen with glutaronitrile electrolyte. The degree of swelling was controlled electrochemically. Subsequently, the distance between the voids formed by the silica beads, which were etched by hydrofluoric acid treatment, could be altered. It should be mentioned that there are also other concepts for electrically switchable photonic crystals that are not directly connected to electrochemically induced solvation [347-349]. 

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