No abstract

Contrast variation in small‐angle neutron scattering (SANS) experiments is used to compare the structures of a water‐based ferrofluid, where magnetite nanoparticles are stabilized by sodium oleate, and its mixture with biocompatible polyethylene glycol, PEG. The basic functions approach is applied, which takes into account the effects of polydispersity and magnetic scattering. Different types of stable aggregates of colloidal particles are revealed in both fluids. The addition of PEG results in a reorganization of the structure of the aggregates: the initial comparatively small and compact aggregates (about 40 nm in size) are replaced by large (more than 120 nm in size) fractal‐type structures. It is postulated that these large structures are composed of single magnetite particles coated with PEG, which replaces sodium oleate. Micelle formation involving free sodium oleate is observed in both fluids. The structures of the fluids remain unchanged with increasing temperature up to 343 K. New and specific possibilities of SANS contrast variation with respect to multicomponent systems with different aggregates are considered.

Tensile creep tests of bulk and ribbon samples of Zr 52.5 Ti 5 Cu 17.9 Ni 14.6 Al 10 metallic glass have been performed over a wide range of heating rates. It has been found that a change of the quenching rate at least by three orders of magnitude exerts little influence on the shear viscosity below the glass transition temperature T g . In all cases, the viscosity is strongly dependent on the heating rate, which can be explained as a result of irreversible structural relaxation with distributed activation energies. It is argued that the volume spectral density of relaxation centers in the high-energy part of the activation energy spectrum ͑AES͒ of irreversible structural relaxation is higher for ribbon samples than that for bulk specimens by about 30%, whereas the low-energy part of the AES remains unchanged. Above T g , the viscosity of bulk samples is always lower than that of ribbons, which may be interpreted in terms of the phase decomposition.