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高分子链所采用的结构和结构动力学。虽然结晶区聚合物链的组织可以用X射线衍射等衍射技术来探测，但薄膜中的大多数聚合物是由没有长程有序性的非晶相组成的。此外，在室温下，聚合物链不会冻结，这严重影响了电子器件中的载流子输运或太阳能电池中的电荷分离等电子机制。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。最强大的分子结构和动力学探测器之一是中子散射(NS)，其中中子与聚合物主链和侧链的相互作用可以作为温度的函数来测量。NS的不同技术允许在不同的环境中探测结构和动力学。准弹性中子散射(QENS)用于探测聚合物动力学，非弹性中子散射用于探测振动模，而小角中子散射(SANS)用于探测链的构象，例如刚性或卷曲的链。尽管NS方法很有潜力，但很少被应用于共轭聚合物，部分原因是对托管大规模设施的访问有限，还因为对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.