1H NMR spin diffusion is shown to advantageously complement scanning electron microscopy (SEM) observations for the characterization of polymer structuring in composite materials. It is here demonstrated on a material containing a few percent of polymer binder and a crystalline organic/inorganic mixture as reinforcement. In SEM observations, polymer accumulations are seen. However, the polymer is also expected to fill small porosities and thin layers at the interface of particles to ensure the cohesion and the mechanical properties of the assembly. In most cases, this polymer structuring is invisible considering the resolution and contrast achieved by SEM on such material. It is thus investigated taking advantage of the two‐step decay of nuclear magnetic resonance spin diffusion curves. Average thickness values of 30 and 188 nm are estimated for the interphase and the overall polymer, respectively. Such structural information improves the knowledge of structure/property relationships and provides better understanding of material properties and making processes.

1IntroductionSolid explosives displays trongly heterogeneous microstructures, which are known to evolveu nderp rocessing, thermal treatments, and mechanical loads. In turn, microstructure evolutions may affect macroscopic properties, such as shock and impact sensitivity,o rt hermo-mechanicalb ehavior.T herefore, it is of crucial importancet oc haracterizee xplosives microstructures and their evolutions. The subject can still be considered to be in its infancy,b ut has grown significantly in recent years.G iven the complexity of the considered microstructures and the variety of spatial scales involved, having recourse to various techniques of investigation is the only way of improving the current level of knowledge in this domain.Opticala nd scanning electron microscopy are almost routinelyu sed nowadays, eithert oc haracterize microstructures and the influence of processingp arameters on them (see, for example,R ef. [1]), or to perform microstructure level simulations (see, for example, Refs. [2,3]). Besides, ag rowing number of modern techniques mayp rovide useful data related to differenta spectsa nd scales of explosives microstructures and their evolutionu nder variousa pplied thermal or mechanical loads. This is the case of X-ray or neutron small-angle scattering and of X-ray microtomography,u sed to investigate the role of pressing parameters and of thermalt reatmento nt he porosity of explosives [4] or to locate the binder [5].T his is also the case of X-ray diffraction, where the intensities of diffractionp eaks can be analyzed to characterize processing-induced texture. Schwarz et al. [6] studied samples taken at different locations of al arge part of PBX9502 (a plastic-bonded pressed explosive) manufactured by semi-isostaticp ressing.T hey showed that the shear component of the stresses applied duringt he pressingo peration causes crystals rotation such that their [0 02]p lanesc ome preferentially parallel to shear planes, thus inducing as trong texture. Such texture measurements could be correlated to the anisotropy of irreversible thermal expansion, known as "ratchet growth" for this family of materials [7].The width of diffraction peaks can also be analyzed, through the so-called Rietveld analysis, to derive information about the crystallographic structure and structural defects of constitutivec rystals of explosives, namely average crystallite size and microstrain. The crystallite size L,o rc oherent diffraction domain, is the size of the perfect crystal. It can be viewed as an average length between two structural defects in agiven plane family.The microstrain e corresponds to lattice distortion due tos light displacements of atoms and molecules from theirp ositioni na ni deal crystal. These two parameters are considered to represents tructural defects of the material [8] and induce broadeningo fXray diffraction peaks.Afew papers have been published about structural defects andt heir evolutioni ns everal explosives. Herrmann and Fietzek [9]s tudied cyclotrimethylenetrinitramine( RDX) and cyclotetram...