Controlled evaporative self-assembly of poly(3-hexylthiophene) monitored with confocal polarized Raman spectroscopy

Abstract

Highly-ordered, parallel gradient P3HT stripes are fabricated through a facile deposition method based on controlled evaporative self-assembly (CESA). Confocal polarized Raman spectroscopy is employed to determine the orientation of P3HT chains in individual stripes and spacing. This is the first report on orientation at the molecular level, beyond sole morphology, in the patterns assembled by CESA. P3HT chains tend to aggregate into one-dimensional nanowhiskers in solution upon aging, leading to a time-evolved dispersion composed of isolated chains and nanowhiskers. A corresponding evolution of morphology and molecular orientation in the obtained patterns is observed when assembling P3HT solutions with different aging times. The stripes evolve gradually from slim stripes with fingering instabilities for fresh solution into highly regular, perfect stripes for sufficiently aged solution. In the stripe region, P3HT backbone chains align parallel to the contact line for fresh solution whereas perpendicular for aged solution. The thermodynamic multicomponent system gives greater variety to the CESA study.