Linear and Nonlinear\nRheological Investigations of\nPoly(3-hexylthiophene) H‑Aggregated Gel Networks

Owing to its facile synthesis and low cost, poly(3-hexylthiophene)\n(P3HT) has been extensively investigated in the field of organic electronics.\nWell-defined packing of P3HT chains and getting controlled morphologies,\nwhich solely depend on the polarity of the solvent, remain challenging.\nHerein, the aggregation behaviors of P3HT in organic solvents having\ndifferent solvent polarities have been investigated to achieve different\norderings of P3HT chains (H-type or J-type). The aggregation in the\nsolution phase and the subsequent structural as well as morphological\nbehaviors of P3HT chains have been investigated by absorption, X-ray\npowder diffraction, and topological studies, respectively. It has\nbeen noticed from absorption studies that P3HT forms H-type aggregates\nin anisole, phenetole, etc., whereas it produces J-type aggregates\nin toluene. More surprisingly, H-type aggregations of P3HT chains\nat low concentrations (<i>C</i><sub>P3HT</sub> = 0.001 g/cm<sup>3</sup>) eventually lead to the formation of the gel network that\nceases the flow of the solvents. Contrary to expectations, J-type\naggregation in toluene does not produce the gel network at the said\nconcentration. Further, to reveal the viscoelastic and microstructural\nproperties, P3HT gel networks have been thoroughly investigated by\nsmall-amplitude oscillatory shear (SAOS) and large-amplitude oscillatory\nshear (LAOS) with varying concentrations, solvents, and molecular\nweights of P3HT. With quantitative analysis, the nonlinear rheological\ncharacteristics of higher harmonics, strain-stiffening ratio, shear-thinning\nratio, dissipation ratio, intracycle transient moduli, and derivative\nof transient moduli have been evaluated for P3HT networks, which significantly\nprovide the rheological information for the understanding of conducting\npolymer networks.