Interrogating the dynamics of conjugated polymers using neutron scattering & molecular dynamics

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The electronic and optical properties of conjugated polymers depend critically upon the structuresadopted by the polymer chains and the structural dynamics. Whilst the organisation of polymerchains in crystalline regions can be probed using diffraction techniques such as X-ray diffraction, mostof the polymer in a thin film is composed of amorphous phases with no long-range order. Moreover,at room temperature the polymer chains are not frozen, and this strongly affects the electronicmechanisms such as charge carrier transport in electronic devices or charge separation in solar cells.Structure and dynamics can be simulated using atomistic molecular dynamics, but experimentalprobes of structure are required to validate the models. One of the most powerful probes ofmolecular structure and dynamics is neutron scattering (NS), where the interactions of neutrons withthe polymer backbone and side chains can be measured as a function of temperature. Differenttechniques of NS allow to probe the structure and dynamics in different environments. Quasi-elasticneutron scattering (QENS) probes the polymer dynamics, inelastic neutron scattering is used to probevibrational modes, while small angle neutron scattering (SANS) is used to probe the conformation ofchains, for example, whether rigid or coiled. Despite of their potential, NS methods have seldom beenapplied to conjugated polymers partly because of the limited access to the hosting large scalefacilities, and also because the interpretation of resulting data is complex.