All-conjugated block copolymers are an emerging class of polymeric materials promising for organic electronic applications, but further progress requires a better understanding of their microstructure including crystallinity and self-assembly through micro-phase segregation. Here, we demonstrate remarkable changes in the thin film structure of a model series of all-conjugated block copolymers with varying processing conditions. Under thermal annealing, poly(3-hexylthiophene)-b-poly(9',9'-dioctylfluorene) (P3HT-b-PF) all-conjugated block copolymers exhibit crystalline features of P3HT or PF, depending on the block ratio, and poor π-π stacking. Under chloroform solvent annealing, the block copolymers exhibit lamellar ordering, as evidenced by multiple reflections in grazing incidence wide- and small-angle X-ray scattering (GIWAXS and GISAXS), including an in-plane reflection indicative of order along the π-π stacking direction for both P3HT and PF blocks. The lamellae have a characteristic domain size of 4.2 nm, and this domain size is found to be independent of block copolymer molecular weight and block ratio. This suggests that lamellar self-assembly arises due to a combination of polymer block segregation and π-π stacking of both P3HT and PF polymer blocks. Strategies for predicting the microstructure of all-conjugated block copolymers must take into account intermolecular π-π stacking and liquid crystalline interactions not typically found in flexible coil block copolymers.
Control of the crystallization of conjugated polymers is of critical importance to the performance of organic electronics, such as organic photovoltaic devices, due to the effect on charge separation and transport, particularly for allpolymer devices. The block copolymer poly(3-dodecylthiophene)-block-poly(9,9-dioctylfluorene) (P3DDT-b-PF), which has matched crystallization temperatures for each block, is used to study the effects of processing history on resulting crystallization. For longer annealing times and rapid quenching to room temperature, P3DDT crystals are preferred whereas for shorter annealing times and slower quenching, PF crystals are preferred. Both crystal forms are evidenced for long annealing time and slow quenching. Additionally, for room temperature annealing in the presence of a chloroform vapor, PF crystals are found in the PF b phase with the predominant crystal peak oriented perpendicular to the thermally annealed case. These results will provide guidance for optimizing annealing strategies for future donor/acceptor block copolymer photovoltaic devices. V C 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2014, 52, 900-906
Recent experimental studies have revealed that conventional casting powders have two kinds of shear-thinning mechanisms in different ranges of temperature: 1) shear-thinning at high temperatures by the alignment of molecular structures, [1,4,5] and 2) shear-thinning near the break temperature due to the
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