Conjugated Polymer Blends—X-Ray and Neutron Scattering Analysis of Structure and Relationships to Electronic Properties

Blends of conjugated and commodity polymers allow for design and balance between the conjugated polymer’s electronic properties and the commodity polymer’s variable physical properties. This balance is vital in flexible wearable organic electronics such as electronic skin, biosensors, or haptics, which require increased flexibility and durability, while still maintaining good electronic performance. Understanding the fundamental interactions between conjugated polymers and the matrix polymers is essential for designing and optimizing organic electronic devices. It is often difficult to study such materials with microscopy techniques, due to reduced contrast between components, as well as the small length scales that are involved. Through the use of selectively deuterated components and careful system design, small angle x-ray and neutron scattering (SAXS, SANS) can be used to investigate the nano and micro scale structures. Using these scattering methods, we have probed the morphology of conjugated polymer blends in both solid and solution states, allowing us to characterize both the phase separated domains and self-assembled structures of the conjugated polymers.<br/>Initial research on polystyrene and conjugated polymer blends has shown strong relationships between morphology and resulting electronic properties [1]. Recently, solution state SANS with contrast matching was used to investigate the effect of the matrix polymer on the phase separation and assembly of the conjugated polymer. Moreover, the work has also been expanded to study blends of conjugated polymers with thermoplastic elastomeric-triblock copolymers (PS-PI-PS and PS-PBD-PS). SAXS and USAXS were used to examine the phase separated structure of the tri-block matrix polymer as a function of the conjugated polymer concentration and identity. We observed a significant shift in the characteristic peak of the tri-block polymer, indicating that the addition of the conjugated polymer forced the tri-block’s phase-separated lamellar structure to swell. We have also observed alignment of the lattice structures with the addition of heat and shear forces, suggesting a process for manipulating the orientation of the lattice for material optimization. We aim to develop models to relate the morphology of elastomeric conjugated polymer blends to their composition and processing and to identify relationships between resulting structures and the electronic properties. Ultimately, we aim to inform the optimization of flexible conductive polymeric materials.<br/>[1] Wolf, C. M. <i>et al.</i> Blend Morphology in Polythiophene−Polystyrene Composites from Neutron and X-ray Scattering. doi:10.1021/acs.macromol.0c02512