Linear and Nonlinear Rheological Investigations of Poly(3-hexylthiophene) H-Aggregated Gel Networks

Owing to its facile synthesis and low cost, poly(3-hexylthiophene) (P3HT) has been extensively investigated in the field of organic electronics. Well-defined packing of P3HT chains and getting controlled morphologies, which solely depend on the polarity of the solvent, remain challenging. Herein, the aggregation behaviors of P3HT in organic solvents having different solvent polarities have been investigated to achieve different orderings of P3HT chains (H-type or J-type). The aggregation in the solution phase and the subsequent structural as well as morphological behaviors of P3HT chains have been investigated by absorption, X-ray powder diffraction, and topological studies, respectively. It has been noticed from absorption studies that P3HT forms H-type aggregates in anisole, phenetole, etc., whereas it produces J-type aggregates in toluene. More surprisingly, H-type aggregations of P3HT chains at low concentrations (C_P3HT = 0.001 g/cm³) eventually lead to the formation of the gel network that ceases the flow of the solvents. Contrary to expectations, J-type aggregation in toluene does not produce the gel network at the said concentration. Further, to reveal the viscoelastic and microstructural properties, P3HT gel networks have been thoroughly investigated by small-amplitude oscillatory shear (SAOS) and large-amplitude oscillatory shear (LAOS) with varying concentrations, solvents, and molecular weights of P3HT. With quantitative analysis, the nonlinear rheological characteristics of higher harmonics, strain-stiffening ratio, shear-thinning ratio, dissipation ratio, intracycle transient moduli, and derivative of transient moduli have been evaluated for P3HT networks, which significantly provide the rheological information for the understanding of conducting polymer networks.