###### Abstract  
Ultra-small-angle neutron scattering (USANS) experiments are reported on isotropic magnetoactive elastomer (MAE) samples with different concentrations of micrometer-sized iron particles in the presence of an in-plane magnetic field up to 350 mT. The effect of the magnetic field on the scattering curves is observed in the scattering vector range between 2.5 \(\times\) 10\({}^{-5}\) and 1.85 \(\times\) 10\({}^{-4}\) A\({}^{-1}\). It is found that the neutron scattering depends on the magnetization history (hysteresis). The relation of the observed changes to the magnetic-field-induced restructuring of the filler particles is discussed. The perspectives of employing USANS for investigations of the internal microstructure and its changes in magnetic field are considered. ultra-small-angle neutron scattering; magnetoactive elastomer; magnetorheological elastomer; hysteresis; restructuring of the filler +
Footnote †: journal: Applied  
**Citation**: [PERSON] [PERSON]; [PERSON]; [PERSON]; [PERSON] [PERSON] Feasibility of Probing the Filler Restructuring in Magnetoactive Elastomers by Ultra-Small-Angle Neutron Scattering. [PERSON] et al. [25] developed a Small Angle Light Scattering (SALS) laboratory setup with simultaneous exposure of fluidic samples to a shear flow and an external magnetic field and used it for investigation of structuring processes in a magnetic fluid comprising clustered iron oxide nanoparticles. They observed an anistropy of the scattering patterns in an applied magnetic field. [PERSON] et al. [26] reported a magnetorheological SANS setup at the Institut Laue-Langevin allowing for an in-situ magnetic field up to 20 mT and the shear flow of ferrofluids. The maximum magnetic field in this setup is one order of magnitude below the magnetic-field values required to observe the effects caused by magnetic-field restructuring in MAEs. Conventional SANS is an experimental technique that uses elastic neutron scattering at small scattering angles to investigate the structure of various substances at a mesoscopic scale of about 1-100 nm. Therefore, it has been neglected for investigation of MAEs, where micro-particles are employed. In the present paper, we use the ultra-small-angle neutron scattering (USANS) instrument S18 at the Institut Laue-Langevin where the length scale that can be analyzed is extended beyond 10 \(\upmu\)m.  
The displacements of magnetic particles in MAEs can be observed by using X-ray micro-computed topography, but this method becomes unreliable at high concentrations of filler particles due to X-ray absorption. It is known that SANS allows one to determine the fractal organization of a cluster (mass fractal) because a certain correlation between particles occurs in the case of their aggregation. It is also largely accepted that the reduction of the shear storage modulus of filled elastomers with the growing amplitude of shearing oscillations (known as the Payne effect) in nanocomposites can be attributed to the agglomeration/de-agglomeration of filler-particle aggregates and is determined by the fractal dimension of the cluster. Very recently, it was hypothesized that USANS may be used to determine the magnetic-field-induced changes of fractal dimension of aggregates of ferromagnetic particles in MAEs [27]. In general, it can be expected that if a rearrangement of magnetized inclusions takes place in a magnetic field, such a change in a microstructure should be observable in a USANS experiment if the size of particles or their aggregates is comparable with the magnitude of the observable scattering vector. Given some similarity between operation modes of MAEs and magnetic fluids, it would be interesting to obtain additional information on the internal microstructure of MAEs using neutron scattering techniques, as it has been successfully done in magnetic fluids.