Supramolecular Assembly of Oriented Spherulitic Crystals of Conjugated Polymers Surrounding Carbon Nanotube Fibers

Controlling the organization and stretchability of poly(3-butylthiophene) spherulites

In this work, we report a simple strategy to readily prepare poly(3-butylthiophene) (P3BT) films with patterned spherulites by brushing the P3BT film surface and annealing the film with carbon disulfide (CS₂) vapor. The spherulites nucleated preferentially at the mechanically scratched areas over the unscratched region of the film. The ridge (formed at the side of the scratch) hinders the diffusion of the P3BT molecules, promoting the aggregation and nucleation of P3BT along the ridge to form spherulites upon the CS₂ vapor-annealing. The sizes of the ridge and the scratch have no effect on the nucleation and crystallization of the patterned spherulites. We evaluated the crack formation of the P3BT films with patterned spherulites in response to mechanical stretching along different directions. When the stretching direction was parallel to the scratching direction, cracks appeared preferentially at the boundary between the ordered spherulites. In contrast, cracks occurred first at the boundary of stochastic nucleated spherulites located away from the patterned spherulites, when the stretching direction was perpendicular to the scratching direction. The patterned spherulites with regulated mechanical properties may find applications in the design and fabrication of stretchable organic optoelectronic devices with enhanced stability and durability.

Chromatic Conductive Polymer Nanocomposites of Poly (p-Phenylene Ethynylene)s and Single-Walled Carbon Nanotubes

We report on dispersions and thin films of chromatic conductive nanocomposites of poly(p-phenylene ethynylene)s (PPEs) and single-walled carbon nanotubes (SWNTs) generated via solution mixing. The linear, conjugated PPEs with dialkyl- and dialkyloxy-side chain groups are shown to debundle and disperse high concentration (up to 2.5 mg/mL) SWNTs in various organic solvents. The solubilization of SWNTs and PPE wrapping is accompanied with the change in the solution color. Ultraviolet visible absorption spectra of nanocomposite solutions demonstrate a new absorption peak at a higher wavelength, supporting the observed chromatism. Fluorescence spectra of nanocomposite solutions display significant quenching of the fluorescence intensity and the Stern–Volmer model is used to analyze fluorescence quenching. Electron microscopy of the chromatic solid films of high mass fraction PPE/SWNT nanocomposites obtained by vacuum filtration reveals the debundled SWNTs in the PPE matrix. The tensile strength and Young’s modulus of these PPE/SWNT nanocomposite films are as high as 150 MPa and 15 GPa, respectively. The composite films exhibit remarkably high conductivities, ranging from ~1000 S/m to ~10,000 S/m for 10 wt% and 60 wt% SWNT nanocomposites, respectively.

Phase Behavior of Amorphous/Semicrystalline Conjugated Polymer Blends

We report the phase behavior of amorphous/semicrystalline conjugated polymer blends composed of low bandgap poly[2,6-(4,4-bis(2-ethylhexyl)-4H-cyclopenta [2,1-b;3,4-b′]dithiophene) -alt-4,7(2,1,3-benzothiadiazole)] (PCPDTBT) and poly{(N,N′-bis(2-octyldodecyl)naphthalene -1,4,5,8-bis(dicarboximide)-2,6-diyl)-alt-5,5′-(2,2′-bithiophene)} (P(NDI2OD-T2)). As usual in polymer blends, these two polymers are immiscible because ΔS_m ≈ 0 and ΔH_m > 0, leading to ΔG_m > 0, in which ΔS_m, ΔH_m, and ΔG_m are the entropy, enthalpy, and Gibbs free energy of mixing, respectively. Specifically, the Flory–Huggins interaction parameter (χ) for the PCPDTBT /P(NDI2OD-T2) blend was estimated to be 1.26 at 298.15 K, indicating that the blend was immiscible. When thermally analyzed, the melting and crystallization point depression was observed with increasing PCPDTBT amounts in the blends. In the same vein, the X-ray diffraction (XRD) patterns showed that the π-π interactions in P(NDI2OD-T2) lamellae were diminished if PCPDTBT was incorporated into the blends. Finally, the correlation of the solid-liquid phase transition and structural information for the blend system may provide insight for understanding other amorphous/semicrystalline conjugated polymers used as active layers in all-polymer solar cells, although the specific morphology of a film is largely affected by nonequilibrium kinetics.