Multi-Scale Assembly of Polythiophene-Surfactant Supramolecular Complexes for Charge Transport Anisotropy

Abstract

Multiscale assembly of poly­(3-alkylthiophene)­s complexed with various alkyl-chain surfactant architectures has been investigated in dilute and concentrated solutions by means of ultraviolet–visible absorption and fluorescence spectroscopy, polarized optical microscopy, small-angle X-ray scattering, and four-point probe conductivity measurements. Supramolecular complexation occurs via ionic interactions between poly­(3-alkylthiophene)­s electrolytes and ionic surfactants. In dilute solutions, the supramolecular complex undergoes a coil-to-rod conformational transition as evidenced by a time-dependent chromism. Spectroscopic studies on transition kinetics reveal an inverse first-order rate law. While surfactant architectures significantly affect the persistence length of the complexes, the inverse first-order rate law is maintained. When concentrated above a critical value, the supramolecular complex exhibits an isotropic-to-liquid crystalline transition yielding hexagonally ordered microstructures. The liquid crystalline phase boundaries are largely dependent on polymer and surfactant architectures. The correlations between the intrinsic rigidity of conjugated polymers, optoelectronic properties, and liquid crystalline formation are presented. The dried films made from the sheared liquid crystalline solutions inherit liquid crystalline monodomains and display four times faster charge transport along the backbone alignment direction than the perpendicular direction.

Ordered Nanostructures of Carbon Nanotube–Polymer Composites from Lyotropic Liquid Crystal Templating

“…The scattering peaks of integrated SAXS data occur with a q * /q ratio of 1: (Figure a) and the 2D SAXS pattern (Figure b) appears to arise largely from a single crystal with sixfold symmetry. This observation is consistent with the expected hexagonal symmetry from the hexagonal LLC mesophase . The similar hexagonal structures have been observed in all LLC monomer surfactants as shown in Figure c.…”

“…In general, LLC materials are susceptible to the external fields such as shear flow, electric and magnetic fields . As such, the defect‐free monodomain structures of LLC phases could be obtained under appropriate conditions and subsequently locked in the solid films after polymerization.…”

Hydrogen-Bonding-Directed Ordered Assembly of Carboxylated Poly(3-Alkylthiophene)s

“…For the only coil-to-rod transition, our previous work shows kinetics that demonstrates inverse first-order behavior ( S coil–rod ∝ C –1 ) in the P3AT supramolecular complexes. 25 For the sole rod–rod aggregation, scaling establishes a nucleation rate that is proportional to the concentration raised to the second power ( S aggreg ∝ C 2 ). 50 In contrast, the chain-folding process reveals the kinetics of a fractional order.…”

“…5,37,55 As such, the long-range directional order may be supported in P3C5T microstructures through parallel alignment of the polymer long axis. 25,56 Using the POM approach, the boundary between the isotropic and nematic LC phases of P3C5T was determined to be 21 ± 1 wt % (Figure 8). Interestingly, this critical concentration of the nematic LC formation is of the same order as the threshold of gelation.…”

“…As the long axis (conjugated backbone) of P3C5T chains is oriented parallel to the shear direction, greater charge transport is observed through the intramolecular pathways as opposed to intermolecular hopping through π–π stacking. 25 The error in the conductivity values is associated with instrumental limitations for measuring film thickness. Nevertheless, the uniformity in relative film thickness between measurements suggests that the difference in conductivity between the parallel and perpendicular orientations is accurate.…”