RESUMEN
The properties of thin liquid films are usually investigated under static conditions, isolated from external disturbances. Such studies provide vital information about the drainage mechanism of the thin liquid film, but the conditions of these measurements are vastly different from those that occur when a real dispersed system is created. In this paper, we present elaborated methodologies that allow qualitative and quantitative measurements of the stability of both the emulsion and foam films formed by a single bubble and droplet at liquid/gas and liquid/liquid interfaces, where the hydrodynamic factors are of crucial importance. The experiments were performed in a bovine serum albumin (BSA) solution at different pH values. The adsorption behavior of BSA under different pH conditions at the liquid/gas and liquid/liquid interface is described, and its implication for the single bubble/droplet motion and liquid film drainage is analyzed. The mechanism of thin-liquid-film stabilization by the BSA molecules is shown to be significantly different for the foam and emulsion films and depends significantly on the bubble history as well as the pH of the BSA solution. Additionally, the results obtained for BSA were compared to those acquired for a typical surface-active substance, sodium lauryl sulfate. The similarities and differences in the rising bubble/droplet dynamics (caused by different dynamic adsorption layer architectures) and foam and emulsion film stabilization by these two types of stabilizers under dynamic conditions are shown and discussed.
RESUMEN
Nickel-silver core-shell (Ni@Ag) nanoparticles (NPs) were formed in a two-step process: (1) the formation of a dispersion of Ni NPs; and (2) the transmetalation (galvanic displacement) reaction, where the surface of the Ni NPs acted as the reducing agent of Ag ions. Ni NPs were synthesized by the 'wet' chemical method, i.e., by the reduction of metal ions by using NaBH4 as the reducing agent. The influence of the concentration of polymeric stabilizer, reducing agent and Ag precursor on the properties of synthesized NPs was evaluated. In the optimal condition of synthesis, Ni@Ag NPs with about 50 and 210 nm-diameter Ni core coated with a thin (â¼10-20 nm) Ag shell, were obtained. Finally, the stability of the synthesized spherical-shaped Ni@Ag NPs was tested and the results indicate long-term stability against aggregation and Ni oxidation. Thus, the resulting NPs are promising candidates for application in electronic devices, e.g., as components of conductive inks or pastes.