The influence of counterions and co-ions on the stability and thickness of foam films stabilized by anionic dodecyl sulfate (DS(-)) has been studied in a thin film pressure balance. Particularly, the effect on the properties of foam films of (i) the counterions Li(+), Na(+), and Cs(+) of DS(-) and (ii) monovalent inorganic salts added to sodium dodecyl sulfate solutions is considered. Generally, addition of salt improved the stability of the foam films. As a second order, an increasing ionic size led to an increased adsorption, which in the case of cations gave thinner and less stable films and in the case of anions led to thicker and more stable films. Hence, an effect of anions was observed though the film surfaces were already negatively charged by the anionic DS(-), leading to the conclusion that adsorption of anions to the film surface is governed by ion specific rather than electrostatic interactions. At a fixed surfactant and varying salt concentration, a maximum in film thickness could be identified at a salt concentration well below the surfactant concentration. We anticipate that (i) at low salt concentration salt mainly affects the charging of a film interface, whereas (ii) at high salt concentration salt mainly affects the screening of the electrostatic repulsion between the two interfaces of the film.

A novel, simple, and very efficient method to prepare hydrophobically modified gold particles is presented. Gold nanoparticles of different sizes and polydispersities were prepared. The diameter of the gold particles ranges from 5 to 37 nm. All systems were prepared in aqueous solution stabilized by citrate and afterwards transferred into an organic phase by using amphiphilic alkylamine ligands with different alkyl chain lengths. The chain length was varied between 8 and 18 alkyl groups. Depending on the particle size and the alkylamine, different transfer efficiencies were obtained. In some cases, the phase transfer has a yield of about 100%. After drying, the particles can be redispersed in different organic solvents. Characterization of the particles before and after transfer was performed by using UV/Vis spectroscopy, transmission electron microscopy (TEM), and small-angle X-ray scattering (SAXS) techniques. The effect of organic solvents with various refractive indices on the plasmon band position was investigated.

Negative charges at the air/water interface have been proven previously by the authors via disjoining pressure measurements of wetting films. In the present study the surface charges of wetting film are modified in order to control the film stability. Studies at different pH values support the assumption that the negative charges are caused by an excess of hydroxide ions. Addition of different types of salt anions seems to lead to an increase in surface charges with decreasing hydration shell. Both water-soluble and water-insoluble amphiphiles replaces the charges. The air/water surface remains negatively charged in case of non-ionic surfactant (dodecyl-beta maltoside, C12G2) and anionic ampihiphiles (stearic acid and SDS). The charge will be reversed in case of cationic amphiphiles. Under all of those conditions, films against likely charged solid surfaces are stable and unstable against oppositely charged solid substrates. For this purpose, the charge of silicon wafers was precoated with polyelectrolytes before. At concentrations well below the CMC cationic surfactants are not able to reverse the charges at the air/water interface. Respective wetting films are less stable and show a partial dewetting even on likely charged surfaces. These results lead to the conclusion that the films are stabilised by electrostatic repulsion. Potential adsorption of water-soluble surfactants on oppositely charged surfaces is also taken into account and is studied by contact-angle measurements.

Specific ion effects are of high impact in colloid science and dominate processes in aqueous systems from protein folding or precipitation to ordering of particles or macromolecules in bulk solutions. Due to the large internal interface of colloidal systems especially interfacial ion effects are of importance. This paper presents a new insight into the specific ion effects at the air/water interface of monovalent electrolyte solutions and their consequences for long-range interactions in colloidal systems. Solely, in an asymmetric film (i.e. wetting film) one can determine the sign and precise value of the surface potential of the free air/water surface. It is shown that the all over charges of the interfacial region, which are affected by the type of ion, dominate the interfacial forces even over several tens of nm. This is of interest for tailoring the stability of colloidal systems. It is clearly shown that the air/water interface is negatively charged and that both anions and cations affect the surface potential even at very low electrolyte concentrations (10 À4 M).