Session: Undergraduate Research in Polymer Science:

Electrically conducting conjugated polymers undergo reversible changes in electrical properties as a function of oxidation state and are also electrochromic by nature, meaning that their color and optical properties change reversibly in response to electrochemical oxidation and reduction. Over the years, a significant focus of electrochromic polymer (ECP) research has been designing materials that switch reversibly between a colored and colorless state, as they are promising candidates for smart displays because of their ability to switch color with a low voltage input (< 2 V). Typically, electrochromic devices and displays use expensive transparent conductive substrates such as indium tin oxide (ITO), but the high cost of ITO is prohibitive for mass producing low-ticket items like printed smart labels, where it accounts for up to 80% of the cost. It has been shown that ECPs with conductivities > 1 S/cm can switch between different colored states in seconds over several millimeters without an underlying ITO layer. This demonstrates that even relatively poorly conducting ECPs can potentially replace the ITO while still serving as the color changing element in EC labels. Expanding the color palette of ECPs that can fulfill both roles could potentially be achieved using ECP blends. This means a less conductive ECP (< 1 S/cm) with a desirable color may be suitable for ITO-free labels if the color-changing properties (speed and contrast) are improved by blending the ECP with small quantities of a highly conductive ECP (100+ S/cm). We will show how the quantity of conducting ECP in each blend influences the electrical, electrochemical, and color changing properties of these materials and how this straightforward blending approach can be used to expand the color space of smart EC labels.

Schematic of ECP blending and its use with an ITO-free smart label

Schematic of ECP blending and its use with an ITO-free smart label

Anna Osterholm

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