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Adsorption equilibriums in aqueous aluminum and iron oxides nanosuspensions stabilized by SDBS and TX-100 were investigated using UV spectrophotometry. It was established that the non-ionic surfactant TritonX-100 is not adsorbed from aqueous solution on a hydrophilic surface of both aluminum and iron oxide nanoparticles. At the same time adsorption of the anionic surfactant SDBS was observed in both oxides nanoparticles. In the investigated range of concentrations adsorption isotherms SDBS from aqueous solution on the surfaces of nanoparticles Al 2 O 3 and γ-Fe 2 O 3 not reach saturation. The share of the particles surface occupied by surfactant molecules were estimated based on the value of an area of molecules SDBS in the adsorption layer, which was derived from the isotherm of surface tension (0.10 nm2). The calculations showed that at the investigated concentrations SDBS Al 2 O 3 employed approximately 30 % of surface of nanoparticles, and for γ-Fe 2 O 3 – up to 10%.

The aggregation of air-dry Al2O3 nanopowders prepared by electrical wire explosion (EWE) and plasma deposition in a gas atmosphere was studied by dynamic laser light scattering during redispersion in water. The specific surface of nanopowders was from 9 to 38 m2/g. It was shown that aqueous suspensions of nanopowders stabilized by a double electric layer with an electrokinetic ξ-potential magnitude of 30–40 mV contain coexisting individual particles and their primary aggregates (35–50 wt %). The average size of the primary aggregate is approximately three times larger than the average size of an individual particle. The former probably consists of a central particle surrounded by the first coordination sphere. As the medium pH varies from 2.5 to 11.5, the electrokinetic potential of the Al2O3 nanoparticle suspension monotonically decreases from +40 to −40 mV. Near the isoelectric point (IEP), aggregation is significantly enhanced, which results in the formation of larger secondary aggregates of 103–104 individual particles. The use of Na citrate as an electrostatic stabilizer prevents the formation such large aggregates, and only an increase in the fraction of primary aggregates and a decrease in the number of individual particles occur near the IEP.

The feasibility of using aqueous suspensions of several metal oxide nanoparticles as contrast agents for ultrasonic cardiovascular visualization has been investigated. Nanopowders of Al, Fe, and Zr oxides were prepared by the electrical explosion of metallic wires, and characteristics such as particle size, specific area, and particle size distribution, were obtained, as were TEM photographs. Dynamic light-scattering data demonstrated that the aggregation of nanoparticles took place in their aqueous suspensions in the function of mean particle size. Acoustic properties of stable suspensions of nanopowders were studied in an experimental model of circulation with simultaneous measurements performed by a commercially available standard ultrasonic apparatus used in medical institutions. The results indicate that the intensity of the reflected echo signal depends on the chemical nature of the metal oxide and the structure of nanoparticles and aggregates that are formed in an aqueous medium. The presented data show the high ultrasonic echo activity of several metal oxides and, at the same time, form a scientific background for a better understanding of the interactions between nanoparticles and the ultrasonic wave.

The particle-size distribution, electrooptical potential, and acid properties of the surface of Al2O3 nanoparticles in aqueous media were studied by dynamic light scattering, electroacoustic spectral analysis, and potentiometric titration. The nanopowder with the mean particle size 22 nm was obtained by the oxidation of aluminum wire in the vapor phase using electrical explosion in oxygen-argon mixture. In spite of the presence of aggregates, aqueous suspensions of nanoparticles, as distinct from suspensions of micropowders, are stable without the addition of special stabilizers because of the spontaneous formation of a double electrical layer on their surface, the electrokinetic potential of which is positive and exceeds 30 mV. The most probable reason for electrostatic self-stabilization of suspensions of nanopowders is the adsorption of Al ions formed in the hydrolysis of aluminum nitrates, small amounts of which are produced in electrical discharges during preparation.