nanometric particles have been produced in the recent years. Colloidal cerium oxide particles of nanometer size are irrevers-These dispersions are of interest because they present a very ibly adsorbed on molecularly smooth mica sheets from bulk disperlarge interface in solution (a few hundreds square meters sions. The approach to equilibrium, the homogeneity and stability per gram). Accordingly, they have a great ability to capture of the adsorbed films, and the effects of pH and solution conditions, ions or organic species and they can be transformed into are determined by means of the surface force apparatus and atomic very effective catalytists once dried. Similarly, particles with force microscopy techniques. Driven by electrostatic interactions large specific surface areas are sought for sintering ceramic between oppositely charged substrate and particles, a dense and powders because the processing temperature can be lowered.
relatively homogeneous flat film composed of ceria nanoparticles
Other applications taking advantage of the small dimensions assembled in a single layer can be obtained. Coating substrates with nanometric particles gives a surface smooth at the nanometer of the nanoparticles concern their use as coatings or as bindscale only, but which is fully representative of a colloidal oxide/ ers (3-6). For most of the applications in the nanotechnolwater interface. Force-distance profiles between such layers and ogy domain, dispersions are the unavoidable intermediaries colloidal stability can thus be compared. The long-range electroand their stability in solution must be ensured.
statics repulsion is consistent with the zeta-potential values mea-
Conversely, the very large surface area to volume ratio sured independently in bulk dispersions. An adhesion at contact has the disadvantage that the stability of nanometric particle between ceria is evidenced and its relation with the intricate colloidispersions is generally obtained for marginal pH and ionic dal stability of the oxide dispersions is demonstrated. The chemical conditions that are often not suitable for industrial applicaorigin for the adhesion between ceria surfaces is further supported tions. From a fundamental point of view, these dispersions by the effect that complexant molecules play. In their presence are challenging systems because the classical theory of colthe ceria layers are protected and adhesion is prevented, with an efficiency increasing in the order nitrate õ acetate õ acetyl ace-loidal stability ( 7) is brought to one of its limits. Indeed, tone. It appears that the stability of nanometric dispersions is in the DLVO (7) (Derjaguin-Landau-Verwey-Overbeek) better achieved by controlling the adhesion at contact rather than framework, the kinetic stability of a dispersion is ensured affecting the long-range electrostatic repulsion. ᭧ 1997 Academic Press by the long-range electrical double layer repulsion between Key Words: nanoparticles; adhesion; complexation surface the particles preventing them from falling into an adhesive forces; colloidal stability.
well due to the ever-present attractive dispersion forces. Thus, primary contact between particles will not be established and the liquid film will not rupture if the compressing Nevertheless, it is well known that dispersions of nano-1 To whom correspondence should be addressed.
metric particles can be stable. Moreover, such dispersions 43