Stöber silica particles having diameters of ca. 100 and ca. 200 nm were prepared and silylated using trimethylsilyl N,N-dimethylcarbamate, achieving a range of surface coverage by trimethylsilyl groups by varying the amounts of silylating agent used. The efficacy of silylation was characterized in terms of hydrophobicity of the particles which was assessed by film balance investigations at water−air interfaces and additionally by imaging the long- and short-range structures of silica particulate layers at water−air interfaces and on mica supports by using Brewster-angle and atomic force microscopies.

The interactions of Sto ¨ber silica nanospheres having diameters of ca. 40, 100, and 200 nm were studied at the water-air interface with a Wilhelmy film balance. The particle sizes and size distribution functions were determined from TEM measurements. According to in situ Brewster angle microscopy investigations and the calculated DLVO interparticle energies, the particles formed weakly cohesive films at the interface; hence, the increasing surface pressure during the compression was attributed to interparticle repulsion. The repulsion energies that were determined from the surface pressure versus surface area isotherms exceeded the calculated DLVO energies by 2-3 orders of magnitude. The extremely high interparticle repulsion was attributed to dipole-dipole interactions. Despite the high interparticle repulsion, the monolayer of the particles was in a weakly cohesive state prior to compression that was attributed to the recently recognized long-range attractions of capillary and electrostatic origin. The particle size dependent particle-particle (p-p) distances at the secondary energy minimum of total pair-interaction versus p-p distances curve were also interpreted in terms of the newly recognized interactions. A computer simulation-assisted method was proposed to estimate the error of assuming a hexagonal array of monodisperse particles, which was then taken into account in the calculation of the p-p distances determined from the pressure-area isotherms.

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We report the hydrothermal synthesis and structure of Fe x Co 1-x alloy nanoparticles with considerable stability against oxidation under ambient atmosphere. Powder X-ray diffractometry (XRD), transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDX), inductively coupled plasma mass spectrometry (ICP-MS), 57 FeMössbauer spectroscopy and magnetization measurements are applied to characterize the composition, morphology, crystal structure, atomic order and magnetic properties of the nanoparticles. As-prepared samples are composed mainly of the bcc Fe x Co 1-x alloy phase.TEM images of heat-treated samples confirm the nanoparticle nature of the original alloys. A consistent analysis of the experimental results leads to x  53% and x  62% Fe atomic ratio respectively in two analogous alloy samples, and suggests that the atomic level structure of the nanoparticles corresponds to that of a fully disordered (A2-type) alloy phase. Exploration of the effect of cobalt on the 57 Fe hyperfine parameters of iron microenvironments suggests that in these alloys the electronic state of Fe atoms is perturbed equally and in an additive manner by atoms in their first two coordination spheres.