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Neutron scattering is a unique, non-invasive probe, into the structure and dynamics of matter spanning lengthscales of Angstroms to microns and timescales of femtoseconds to minutes. NS has contributed dramatically to the understanding of biological systems and complex materials during the past decades. Neutron posses wavelengths (~Angstroms) and energies (~meV) particularly suitable to interrogate matter at the molecular level and benefit from contrast variation by simple isotopic substitution or ubiquitous H and D. A major limitation of the technique, however, has been the access to instrumentation and long measurement times. The advent of unprecedented powerful neutron sources (particularly Oak Ridge National Laboratories) opens exceptional opportunities to accelerate materials discovery and development and, most importantly, to probe qualitatively different phenomena. The latter include fast kinetics or measurements in thin films, for example. Here we provide a few examples of applications of NS in elucidating the structure and dynamics of matter.

Microstructure

Small (and ultra-small) angles neutron scattering determines the micro & mesostructure and thermodynamics of composite materials, mixtures, and nanostructured materials. In this example, the phase transitions and equilibrium behaviour of two highly interacting polymers are investigated. A combination of real (microscopy) and reciprocal space (scattering) techniques yields unique insight into 3D structure and kinetics.

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Neutron reflection provides unique information the interfaces and thin films, both in-plane and off-plane structure and evolution. [Data from Higgins et al] The understanding of the microstructure of multi-layered thin films and laminates is crucial to numerous applications involving energy-efficient advanced materials (including solar cells).

Incoherent inelastic neutron scattering (INS) techniques are extremely powerful for the study of dynamics of glass forming polymers. Neutrons allow analysing polymer dynamics with time and spatial resolution over a broad frequency range, from fast atomic vibrations to segmental motions which take place in the rubbery state. In particular, quasielastic neutron scattering (QENS) is unique for the study of polymer dynamics at a microscopic level. As an example, the figure below shows the QENS spectra for poly(4-methylstyrene)-d4 at 80 K. The black curve represents the instrumental resolution of the spectrometer (IRIS, ISIS, UK).

This QENS broadening (green points) arises from the rotation of the methyl group attached to the 4 position of the phenyl ring in poly(4-methylstyrene). Incoherent elastic scattering measurements can also offer information on the polymer dynamics focusing on the decreasing of the scattered elastic intensity as a function of temperature (increase of mobility). For instance, elastic scans provide a direct measurement of atomic delocalisation, namely the hydrogen mean square atomic displacements, <u^2>, shown here for poly(styrene) measured with backscattering spectrometer IN16 (ILL, France).