Surface Thermodynamics of Hematite/Yttrium Oxide Core−Shell Colloidal Particles

Abstract

Spherical and quite monodisperse particles (average diameter 60 ( 7 nm) of hematite (R-Fe2O3) were synthesized and then covered with a shell of yttrium oxide of variable thickness. A surface thermodynamic study was carried out for these core/shell colloidal particles, using two experimental techniques: contact angle measurements of selected liquids on glass slides uniformly covered by the material and determination of the penetration rates of liquids through thin layers of the solid. Using van Oss et al.'s model of interfacial interactions (van Oss, C. J. Interfacial Forces in Aqueous Media, Marcel Dekker: New York, 1994), the surface free energy, γS, of the particles was characterized in terms of its two components, Lifshitz-van der Waals, γ S LW , and acid-base, γ S AB . The latter is assumed to be the consequence of both the electrondonor, γ S -, and electron-acceptor, γ S + , characteristics of the solid surface. The efficiency of the coating of the hematite core by yttrium oxide is quantified through the comparison of γ S LW , γ S + , and γ S -values for pure hematite and pure Y2O3, with those of the composite particles. It is found that γ S LW does not depend significantly on the nature of the surface considered, ranging from 46 ( 1 mJ/m 2 for pure hematite to 51 ( 1 mJ/m 2 for pure Y2O3. Both the pure and composite particles show negligible electron-acceptor (γ S + )character. Unlike γ S + , the electron-donor parameter, γ S -, is very sensitive to the surface composition. For composite particles γ S -is closer to that of pure yttria than to hematite's. The shell appears to efficiently hide the interfacial interactions of R-Fe2O3, so that the particles are, in most practical respects, essentially yttria. The implications of this fact on the stability of hematite/yttria suspensions are discussed.

Magnetic Properties of Composite Hematite/Yttrium Oxide Colloidal Particles

“…1 and the diffractograms of Fig. 2 suggest, as mentioned above, an increasing efficiency of the coating in the order A < B < C; in our previous investigation on the electrical and thermodynamic properties of the particle/aqueous solution interface (13,14), it was found that sample C showed a behavior most similar to that of yttrium oxide, whereas sample A was more similar to hematite, and type B particles behaved in a somewhat intermediate way. Our susceptibility data in Fig.…”

“…This is the main aim of this work, in which spherical hematite (α-Fe 2 O 3 ) particles are covered by a shell of Y 2 O 3 . In previous works (13,14), it was found that the surface properties (electrical, thermodynamic, chemical) were essentially controlled by the shell. It was expected that, in contrast, the magnetism of these composite units would be controlled by the core: the particles with mixed composition would thus show interesting properties, behaving as Y 2 O 3 in all phenomena related to the particle surface, and as α-Fe 2 O 3 in their response to applied magnetic fields.…”

Synthesis and Characterization of Spherical Magnetite/Biodegradable Polymer Composite Particles

“…Concerning γ − S , it shows large values in magnetite (like in many other inorganic oxides, for instance hematite and yttria, as found in Ref. (38)), which is thus essentially a monopolar, electron-donor material. Its value of γ − S is much larger than that found for PLA (almost zero); when magnetite is covered by a layer of PLA, γ − S is significantly reduced, another proof of the presence of the polymer on the oxide particles.…”

Preparation and characterization of carbonyl iron/poly(butylcyanoacrylate) core/shell nanoparticles

“…In addition, the Lifshitz-van der Waals component of the mixed particles is almost the same as that of the cyanoacrylate polymer, although this component is the least affected (as is usually the case, see, e.g., Ref. [40]). The electron-donor component γ − S shows large values in carbonyl iron (like in many other inorganic oxides, for instance hematite, yttria and magnetite, as found in Refs.…”