On the stability of thin films of pure water.

The stability of water films has been the focus of many researchers in the recent decades. Unfortunately, there is no consensus on the stability of these foam films or on the mechanisms responsible for stabilizing water films. This paper examines the reported results on this matter and scrutinizes them based on speciation analysis of the dissolved species and the recent achievements in the adsorption of inorganic ions on the air/water interface. Our results confirm the key role of surface contamination, interface approach velocity and evaporation in the drainage and lifetime of these water films. It confirms the stabilizing effect of contamination and the destabilizing effect of air-water interface approach velocity. Moreover, the negative sign of the surface/zeta potential of the air/water interface and its dependence on the pH value were explained.

Smart Complex Fluids Based on Two-Antennary Oligoglycines.

Antennary oligoglycines are synthetic products, obtained as a result of preliminary molecular design. Equal-length antennae are built of glycine residues joined through the C end to an oligoamine branching core with an amine group at the N terminus exposed outside. The results of systematic research on the properties of aqueous solutions containing two-antennary oligoglycine with four glycine portions are reported. The central feature is the competition between amphiphilic self-assembly and formation of polyglycine II motifs. A combined procedure is developed to characterize bulk and interfacial structures and coatings. It includes registration of bulk aggregates, examination of interfacial layers at solution/air and solution/solid boundaries, drainage, and stability of liquid films. The obtained results provide new insight into the structure-property relationships in these smart fluids and give essential hints about key factors allied to possible applications in medicine, pharmaceuticals, and environmental protection.

Wetting properties of phospholipid dispersion on tunable hydrophobic SiO2-glass plates.

We study the wetting properties of very small droplets of salty aqueous suspensions of unilamellar liposomes of DMPC (dimyristoylphosphatidylcholine), situated on SiO2-glass surfaces with different levels of hydrophobicity. We evaluated two different measures of hydrophobicity of solid surfaces - receding contact angles and the thickness of wetting films trapped between an air bubble and the solid surface at different levels of hydrophobicity. We established a good correlation between methods which differ significantly in measurement difficulty and experimental setup. We also reveal details of the mechanism of wetting of different surfaces by the DMPC liposome suspension. Hydrophilic surfaces with water contact angles in the range of 0° to 35° are readily hydrophobized by the liposomes and only showed corresponding contact angles in the range 27°-43°. For same range of surface hydrophobicities, there was a clear reduction of the thickness of the wetting films between the surface and a bubble, reaching a minimum in the 35°-40° range. At higher levels of hydrophobicity both pure water and the liposome suspension show similar contact angles, and the thickness of wetting films between a bubble and those surfaces increases in parallel. Our analysis showed that the only force able to stabilize the film under these experimental conditions is steric repulsion. The latter suggests that nanobubbles adsorbed on hydrophobic parts of the surface, and coated with a DMPC layer, may be the cause of the 40-70 nm thickness of wetting films we observe.