Hydrogen-bonding-induced ordered assembly of poly(3-alkylthiophene)s derivatives bearing carboxylic acid groups has been investigated from diluted and concentrated solutions to solid films using ultraviolet–visible absorption spectroscopy, polarized optical microscopy, and four-point probe conductivity measurements. In dilute solutions, the polymer undergoes a spontaneous structural transition from disordered coil-like to ordered rodlike conformations, which is evidenced by time-dependent chromism. Many factors such as alkyl-chain length, types of solvents, and temperature are studied to understand the assembly behavior. Transition kinetics of the assembly process reveals a universal second-order rate law, indicating an intermolecular origin due to hydrogen bonding. When more concentrated, hydrogen bonding drives nematic liquid-crystalline gelation above a critical concentration and the gels are thermally reversible. Under an appropriate balance of mechanical and thermal stresses, uniform liquid-crystalline monodomains are obtained through the application of a mechanical shear force. The dried films made from the sheared solutions display both optical and electrical anisotropies, with a more than 200% increase in charge transport parallel to the direction of shear as opposed to that in the perpendicular one.
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Published in ACS Omega, Volume 2, Issue 11, 2017, pages 8526-8535.
© 2017 American Chemical Society
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Bilger, D. W., Figueroa, J. A., Redeker, N. D., Sarkar, A., Stefik, M., & Zhang, S. (2017). Hydrogen-bonding-directed ordered assembly of carboxylated poly(3-alkylthiophene)s. ACS Omega, 2(11), 8526–8535. https://doi.org/10.1021/acsomega.7b01361