(113g) In Situ Structural, Mechanical and Electrical Property Development During the Self-Assembly of Conjugated Polymer Organogels

Organogels made from p-type conjugated polymers have shown promise as a platform for developing morphologies that benefit charge transport in organic photovoltaic devices.^[1] However, previous studies of conjugated polymer organogels have largely been limited to the equilibrium state. Engineering specific gel structures requires an understanding of the driving forces behind self-assembly as well as the progression of structural intermediates. The latter can be difficult to probe because studying the progression of self-assembly requires non-invasive techniques that can probe evolving structures over all relevant length-scales. Small angle scattering is an ideal technique for this and is employed in this work to study self-assembling P3HT organogels.

Complementary small angle neutron scattering (SANS), AC dielectric spectroscopy and rheology are utilized simultaneously to study the self-assembly of poly(3-hexylthiophene) (P3HT). This talk will shows that nanoscopic structural features of fibrillar P3HT organogels, which are crucial for the optimization of organic photovoltaic devices, evolve throughout the gelation process. By performing cooling (i.e. gelation) and heating (i.e. dissolution) cycles we find substantial structure-property hysteresis that suggests the formation and dissolution mechanisms are drastically different, both of which are proposed in this talk. We also find that P3HT organogels formed in different solvents show differences of more than two orders of magnitude in conductivity. The similarity in nanoscale structural features between these gels suggests that the mesoscale network structure plays a critical role in the determination of charge transport efficiency. This talk demonstrates the importance of controlling self-assembly towards improving charge transport properties and demonstrates the potential to rationally design specific network structures using organogels as a generally applicable platform.

Reference: [1] – Newbloom, G. M.; Weigandt, K. M.; Pozzo, D. C. Macromolecules 2012, 45, 3452-3462.