A new chromic (TouchChromic) thin film. (December 2016)

• Record Type: Journal Article
• Authors: Ram, Manoj K.; Goswami, D. Yogi; Takshi, Arash; Stefanakos, Elias
• Is Part Of: Acta materialia. Volume 121(2016)
• Page Start: 325
• Page End: 330
• Publication Date: 2016-12
• Subjects: Chromic -- TouchChromic -- Conducting polymer -- Electrolyte -- Composite -- Coloration -- Metal; Materials -- Periodicals; Materials science -- Periodicals; Materials -- Mechanical properties -- Periodicals; Metallurgy -- Periodicals; Chemistry, Inorganic -- Periodicals; 620.112
• DOI: 10.1016/j.actamat.2016.09.019
• Languages: English
• ISSNs: 1359-6454

Abstract

Abstract: We present an exciting new development in thin films which enables innovative reversible color change in the film when touched by a metal without any external excitation, i.e. voltage, temperature, light, etc. The thin film structure is simpler than that of electrochromic materials, requiring only a nanocomposite of a conducting polymer and a gel electrolyte deposited on a transparent conductive substrate (TO, ITO, FTO, etc.) These smart nanocomposite thin films, we can call TouchChromic, can be used in windows (i.e., opaque to transparent) and in a number of other applications such as rear view mirrors in vehicles, IR sensors, toys, and camouflage for the military and defense sectors. The color change and color contrast depend on the type of film, its thickness and composition of the electrolyte. For aqueous acidic electrolytes, a molality of less than 0.01 was found to be most effective. The addition of an oxidizer (i.e. ammonium persulfate) in the electrolytic solution increased the speed of color change. The color change occurs only when specific metals touch the electrolyte. Detailed experimental and theoretical results are presented in this paper to explain the behavior of the chromic film in terms of the pH of the electrolyte, work functions (Fermi levels) of corresponding layers (transparent substrate, conductive polymer, electrolyte and metal) and the energy band diagram of the composite structure. Graphical abstract: A schematic of color change in the PANI while in contact with a metal in the presence of an electrolyte (left). The removal of the metal contact reverses reaction from LEU to PNB (right). Image 1