Directed Self-Assembly of Poly(3,3‴-dialkylquarterthiophene) Polymer Thin Film: Effect of Annealing Temperature

Abstract

Self-assembly of π-conjugated polymers in desired manner plays a vital role in structure, orientations, crystalline packing, and also in electrical charge transport properties. Despite this, there is lack of thorough study about the direct formation of smooth, oriented, crystalline, and aligned films using self-assembly property of π-conjugated polymers. In this study, we have discussed the crystallization behavior and an easy method to study face-on orientation, crystallization, and alignment in organic films, giving as an example poly­(3,3‴-dialkylquarterthiophene) (PQT-12). The effect of annealing temperature (80 and 120 °C) is also studied for this polymer film as the ordering of the polymer backbone and side chains highly depends on temperature. We have directed the self-assembly of PQT-12 using facile “floating film transfer method (FTM)” for obtaining crystalline, oriented, smooth, and aligned polymer films directly without further processing. Unpolarized, polarized UV–vis spectra and selected area electron diffraction (SAED) pattern are used to investigate the ordering/crystallinity, orientation, and alignment (optical anisotropy) of PQT-12 polymer films. Further, an easy electrochemical method is explored to study the crystalline and amorphous phases in the polymer films. Atomic force microscopy (AFM) topography is carried out to study the surface morphology, which shows formation of very smooth films with roughness below 1 nm. Raman spectra show the increase in intensity of signal-to-noise ratio (SNR) (1457 cm^–1) and decrease in ratio of SNR intensity (1457 cm^–1/1393 cm^–1) as a function of annealing temperature. Finally, this study helps in improving the charge transport properties of films and is characterized into two modes, perpendicular and along the films surface with the effect of annealing temperature on PQT-12 films