We report pronounced smecticlike ordering in a ferrofluid adjacent to a SiO2 wall. In the presence of small magnetic fields perpendicular to the interface, ordered layers of magnetite nanoparticles form that can extend up to 30 layers. We also show that short ranged ordered structures emerge when the magnetic field direction is parallel to the interface; however, the layering is strongly perturbed. These results have been obtained by in situ neutron reflectometry which gives a detailed microscopic picture of these ordering phenomena. They also reveal the formation of a wetting double-layer which forms the magnetic template for the observed ordering sheets. The implications of these findings are discussed.

Poly(N‐vinylcaprolactam) (PVCL) is a synthetic analogue of biomolecules (enzymes, proteins). It demonstrates a specific hydration and undergoes a coil–globule transition. The PVCL–D2O system (PVCL mass M = 106) has been investigated by small‐angle neutron scattering (SANS) at T = 296–316 K to identify the structural features of the collapse at concentration C = 0.5 wt% near the threshold of the coil overlap. (The collapse leads to the segregation of the phase enriched with polymer at T > 305 K). The SANS experiments at q = 0.1–5 nm−1 (scales from monomer unit to globule gyration radius RG≃ 16 nm) have revealed a stretched coil–globule transformation in the range 305–309 K. Using high‐resolution SANS (q = 0.002–0.02 nm−1) the globule association to form fractal structures (sponge‐like) of surface dimension DF≃ 2.4–2.6 was examined. The coexistence of globules and disordered chains (regions ∼5–10 nm) was found. The growth of the content of globular phase was induced by the conformational transition in disordered molecular fragments from coiled (dimension D≃ 1.8) to stretched chains (D≃ 1.2).

We studied the internal structure of sterically stabilized water- and oil-based ferrofluids in the vicinity of the free interface with a gas by means of x-ray reflectometry and grazing-incidence x-ray diffraction. It was found that in-depth distribution of the magnetic nanoparticles in the layer close to the interface is essentially inhomogeneous. In the case of water-based ferrofluids an enhanced concentration of surfactant and subsequent reduced concentration of the particles were detected in the 100-200-A -thick interface-adjacent layer. Scattering patterns possessing characteristic features of powder diffraction revealed partial ordering of the surfactant in a multilamellar structure. External magnetic fields applied perpendicular to the interface effectively reduced thickness of the depleted layer bringing the particles from the bulk to the surface. However no field-induced correlations between the particles were detected. In the top 500-A -thick layer of an oil-based ferrofluid depletion of the particles density was also present; however, no special arrangement of the surfactant molecules was manifested by the experimental data. Interestingly, for all samples we observed wavy surface deformation appearing in the normal magnetic field of a strength H much smaller than the critical values H_{c} calculated according to the conventional theory of ferrofluid surface instability. This deformation with lateral periodicity of a few millimeters has an amplitude smoothly increasing up to a few microns at H=0.5H_{c} .

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The microstuctural evolution of plastically deformed steels has been studied by small-angle neutron scattering at ambient temperature in the range of momentum transfer q=(4π/λ)sin(Θ/2)=0.01-5 nm -1 where λ is neutron wavelength and Θ is the scattering angle.Samples of austenite stainless steels were pulled on a standard bench to cause a plastic deformation, S=0-60%, up to the fracture of the material. As a result of the deformation an increase of an order of magnitude was observed in the scatterred intensity I(q)~1/[1+(qRC) 2 ] (6-D s )/2 . The analysis of the I(q) distribution has shown the surface fractal nature of the observed nano-scale structures. The evolution of internal surface via intensive growth of pores (size R C~2 0-40 nm) was found and a linear decrease of the surface fractal dimension 2.9≥D s (S)≥2.1 was observed. These findings can be used to design the fracture criteria for materials of industrial application .