Ion and temperature sensor from polydiacetylene

Abstract

Polydiacetylene (PDA) is an interesting class of conjugated polymer having unique chromic properties suitable for many sensing applications. Although extensive research in PDA for sensing applications have been reported, there is still research gaps in understanding of its color transition mechanism and developing it into a convenient to use platform with high sensitivity and selectivity. In this dissertation, polyelectrolyte multilayer (PEM) thin films using either chitosan or poly(ethylenimine) as a polycation and polymerized 10,12-pentacosadiynoic acid vesicles (poly(PCDA)) as a polyanion are successfully prepared. The spherical structures of vesicles, as well as their important chromic properties are retained in the PEM films. Color transition mechanism of poly(PCDA) vesicles probed by electronic absorption spectroscopy indicates two types of sidechain movement: the reversible conformational change of the aliphatic chains and the irreversible hydrogen bond breaking. In the thermochromism, the transition starts with reversible conformational alteration of methylene side chains leading to metastable purple vesicles followed by the hydrogen bonds breaking. In the ethanolochromism and alkalinochromism, the processes are however induced at the vesicle-media interface, directly bringing about the hydrogen bond breaking. The highly selective colorimetric lead ion sensor is developed based on the interaction at the poly(PCDA) vesicle surface using triethylene glycol ester of PCDA (TEGPCDA) as the sensitivity enhancer. Futhermore, thermochromic screen ink is also developed from poly(PCDA) for temperature sensitive labeling.