Polymer electrochromic materials displayers

Electrochromism is a phenomenon displayed by some materials reversibly changing colors. Various materials can be used to construct electrochromic devices, such as transition metal oxides, liquid crystals, photonic crystals, and polymers (Booth and Casey, 2009 Nicoletta et al., 2005 Arsenault et al., 2007 Gamier et al., 1983). Here, we will focus on the electrochromic materials based on polymers. There are several mechanisms to explain the color changes of polymer electrochromic materials like electro-induced oxidation-reduction and electrothermal chromatic transition and so on. 

High-resolution circuitry and active devices employing Langmuir-Blodgett film techniques or polymer-based transistors are being considered for the sophisticated electronics required in future vehicles. Temperature or energy balance in the vehicle could be controlled through conductive polymers or semiconductor deposits on electrochromic windows. Electroluminescent liquid crystals and fluorescent and electrochromic materials used for visual displays show promise for future development. 

Electrochromic polymers (ECPs) materials exhibit a change in transmittance and/ or reflectance of electromagnetic radiation induced by an electrochemical oxidation-reduction reaction (called electrochromism) (Rosseinsky and Mortimer, 2001). The ECPs can be used as electrochromic displays, glasses, and even fabrics (Remmele et al., 2015). A certain set of properties, such as, desired absorption profile, easily accessible redox process and ease of processing are of essential importance for materials to serve as effective electrochromes (Dyer and Reynolds, 2007). 

Conjugated polymers, discovered in the late 1970s, have attracted a variety of attentions because of their unique properties, such as electrical conductivity and color versatility. The conjugated polymers with different colors can be used as ideal electrochromic materials, which have potential applications in sensors, mirrors, displayers, and textiles. Most of their reversible electrochromic behaviors are caused by the electro-induced oxidation-reduction, that is, the reversible change of a chemical species between two redox states under a certain voltage (Niklasson and Granqvist, 2007 Beaujuge et al., 2010). 

Flexible electrochromic devices (ECDs) are becoming increasing important for their promising applications in many areas, such as the portable and wearable electronic devices, including smart windows, functional supercapacitors, and flexible displays. Typically, an ECD consists of four parts of substrate, conductive electrode, electrochromic material, and electrolyte. Enormous efforts have been made to improve the flexibility of ECDs including utilizing flexible polymer substrates and conductive materials. 

Composite films of PB and poly(3-methylthiophene) capitalize on the transparent state of the reduced PB and the similar colored states of both PB and poly(3-methylthiophene) in their respective oxidized states. This composite switches from deep red, a contribution of poly(3-methylthiophene) in the neutral state, to dark blue in the oxidized state [241]. In addition to the additive electrochromic properties displayed by the materials in the composites, the improved adhesion of PB to the polymer films in comparison with electrode surfaces, along with efficient control of the amount of the composite materials deposited, are the advantages seen with this method. 

The combination of various device platforms, along with electrochromic polymers available in colors that span the entire range of the visible spectrum and beyond, allows the construction of displays that can be tailored to fit most needs in real applications. While these devices have shown enhanced performance in colors available, optical memory, and low power consumption as compared to devices constructed of other electrochromic materials, there are still drawbacks to be addressed. 

The alteration of the optical properties for an electrochromic material involves the insertion or extraction of charge. These polymers can be classified into three types, depending on their specific optical states (1) absorption/transmission-type materials made of metal oxides, viologens or polymers such as PEDOT, including at least one colored and one bleached state for smart windows, (2) display-type materials made of polythiophenes without a transmissive state and (3) materials composed of blends, laminates and copolymers including more than two colored states [7],... 

Volume 7 summarizes new trends on liquid crystals, display, and laser materials. The topics include liquid crystals for electro-optic applications, switchable holographic polymer-dispersed liquid crystals, electrochromism and electrochromic materials for displays, materials for solid-state dye lasers, photophysical properties of laser orientational relaxation processes in luminescence, and lasing of dyes and photosensitive materials for holographic recording. 

Additionally, the film formation properties and outstanding mechanical properties of aramids make these polymers suitable for the production of organic light emitting diodes (OLEDs), and specifically polymer hght emitting diodes (PLEDs). Despite this, classical condensation polymers are rarely studied for these applications. Moreover, some luminescence materials also show electrochromism (EC), a phenomenon in which materials exhibit a reversible change in optical properties when they are oxidized and reduced. Electrochromic materials are now been exploited in diverse applications such as mirrors, displays, windows, and earth-tone chameleon materials [95]. 

The apphcation of a high electric field across a thin conjugated polymer film has shown the materials to be electroluminescent (216—218). Until recentiy the development of electroluminescent displays has been confined to the use of inorganic semiconductors and a limited number of small molecule dyes as the emitter materials. Expansion to the broad array of conjugated polymers available gives advantages in control of emission frequency (color) and facihty in device fabrication as a result of the ease of processibiUty of soluble polymers (see Chromogenic materials,electrochromic). 

The development of conducting polymers is naturally related to hopes of feasible technical applications. Thus, conducting polymers are discussed as active battery electrodes [10], electrochromic displays (BCD) [11], anticorrosives [12], sensors [13], electrocatalysts [14], antistatic materials [15], or light-emitting materials (OLED) [16],... 

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