- Electrochromism
Electrochromism is the phenomenon displayed by some
chemical species of reversibly changing color when a burst of charge is applied.One good example of an electrochromic material is
polyaniline which can be formed either by theelectrochemical or chemicaloxidation ofaniline . If anelectrode is immersed inhydrochloric acid which contains a small concentration of aniline, then a film of polyaniline can be grown on the electrode. Depending on the redox state, polyaniline can either be pale yellow or dark green/black. Other electrochromic materials that have found technological application include theviologen s andpolyoxotungstate s. Other electrochromic materials includetungsten oxide (WO3), which is the main chemical used in the production of electrochromic windows orsmart windows .As the color change is persistent and energy need only be applied to effect a change, electrochromic materials are used to control the amount of
light andheat allowed to pass throughwindow s ("smart windows"), and has also been applied in theautomobile industry to automaticallytint rear-view mirror s in variouslighting conditions. Viologen is used in conjunction withtitanium dioxide (TiO2) in the creation of small digital displays. It is hoped that these will replaceLCD s as the viologen (which is typically dark blue) has a high contrast to the bright color of the titanium white, therefore providing a high visibility of the display.
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