Conjugated polymers (CPs) enable a wide range of lightweight, lower cost, and flexible organic electronic devices, but a thorough understanding of relationships between molecular structure and dynamics and electronic performance is critical for improved device efficiencies and for new technologies. Molecular dynamics (MD) simulations offer in silico insight into this relationship, but their accuracy relies on the approach used to develop the model's parameters or force field (FF). In this Perspective, we first review current FFs for CPs and find that most of the models implement an arduous reparameterization of inter-ring torsion potentials and partial charges of classical FFs. However, there are few FFs outside of simple CP molecules, e.g., polythiophenes, that have been developed over the last two decades. There is also limited reparameterization of other parameters, such as nonbonded Lennard-Jones interactions, which we find to be directly influenced by conjugation in these materials. We further provide a discussion on experimental validation of MD FFs, with emphasis on neutron and X-ray scattering. We define multiple ways in which various scattering methods can be directly compared to results of MD simulations, providing a powerful experimental validation metric of local structure and dynamics at relevant length and time scales to charge transport mechanisms in CPs. Finally, we offer a perspective on the use of neutron scattering with machine learning to enable high-throughput parametrization of accurate and experimentally validated CP FFs enabled not only by the ongoing advancements in computational chemistry, data science, and high-performance computing but also using oligomers as proxies for longer polymer chains during FF development.

In this work, contrast-variation small-angle and ultra-small-angle neutron scattering are used together with wide-angle X-ray scattering (WAXS) to characterize the bulk molecular conformation and self-assembly of polythiophene-based conjugated polymers (CPs) in bulk blends with deuterated polystyrene (PS-d 8) as the matrix component. A significant and sharp transition from small to large globular domains is observed in the phase-separated morphology of all blends as a function of CP concentration. Evidence of self-assembly into nanofiber networks is also observed in regio-regular poly­(3-hexylthiophene) (RRe-P3HT) blends and found to be promoted by the use of solvents of moderate quality (i.e., toluene) during the film formation process and by higher CP loadings when using solvents of good quality (i.e., chloroform). Finally, WAXS and conductivity measurements demonstrate a strong correlation between the degree of crystallinity of the CP in the π-stacking direction (nanofiber formation) and the electronic conductivity across the bulk of the film. In addition to RRe-P3HT, PS-d 8 blends with semi-crystalline poly­(3-dodecylthiophene) (P3DDT) or poly­(3,3‴-didodecyl­[2,2′:5′,2″:5″,2‴-quaterthiophene]-5,5‴-diyl) (PQT-12) and blends with amorphous regio-random poly­(3-hexylthiophene) (RRa-P3HT) were investigated over concentrations ranging from 0.1 to 50 wt % of CP. This work highlights the importance of understanding the factors that influence the phase morphology in blends of CPs and commodity polymers, as this directly alters charge transport pathways and performance of the organic electronic devices that rely on these materials.

We have designed an open-source and high-throughput thermal analysis system for fast and accurate estimation of phase transition temperatures for up to 96 samples analyzed simultaneously. The results are comparable to current state of the art systems such as differential scanning calorimetry (DSC), which is costly and time-consuming. The PhasIR hardware system utilizes an infrared camera to optically record thermal processes that result from the melting/freezing and/or evaporation of samples, while the accompanying open-source software package allows for subsequent batch analysis and processing to extract phase transition temperatures. The PhasIR system showed good agreement with DSC results for both pure substances and mixtures, such as deep eutectic solvents (DES). The all-in-one hardware and software system can be easily replicated and built using relatively inexpensive components at a total estimated cost of $1,080 USD. Implementation of the PhasIR system will allow for increased throughput in material thermal characterization and broader investigation of material design spaces. METADATA OVERVIEWMain design files: https://github.com/pozzo-research-group/phasIR Target group: Scientists requiring high-throughput thermal analysis of organic samples (e.g. pharmaceuticals, polymers, food ingredients, greases, solvents). Skills required: CNC machining, 3D printing, basic electronics and programming.

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