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

共轭聚合物的电子和光学性质主要取决于聚合物链所采用的结构和结构动力学。虽然可以使用衍射技术（如x射线衍射）来探测聚合物在晶体区域的组织，但薄膜中的大多数聚合物是由无长程有序的无定形相组成的。此外，在室温下，聚合物链不会冻结，这强烈影响电子机制，如电子设备中的电荷载流子传输或太阳能电池中的电荷分离。结构和动力学可以用原子分子动力学来模拟，但需要结构的实验探针来验证模型。中子散射（NS）是研究分子结构和动力学最有力的探针之一，它可以测量中子与聚合物主链和侧链的相互作用，并将其作为温度的函数。不同的NS技术允许在不同的环境中探测结构和动态。准弹性中子散射（QENS）探测聚合物动力学，非弹性中子散射用于探测振动模式，而小角中子散射（SANS）用于探测链的构象，例如刚性或卷曲链。尽管具有潜力，但NS方法很少应用于共轭聚合物，部分原因是托管大型设施的访问有限，也因为结果数据的解释很复杂。

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.