Simultaneous measurement of the thickness and the lifetime of a foam lamella.

Despite the important role of foams in industrial applications, few methods for determining the stability are present. By extending the existing light reflection-based apparatus, additional information about a single foam lamella can be obtained. Evaluation of these data delivers insight into the thinning process of the lamella.

The influence of lanthanide-(III)-nitrates on adsorbed monolayers of dodecylphosphorylcholine at the air-water interface.

Adsorption layers at the air-water interface formed from the soluble zwitterionic surfactant dodecylphosphorylcholine (DPC) serving as a soluble model substance for phospho-lipids were characterized with respect to their equilibrium and dynamic surface properties. To clarify the effect of ionic interactions with electrolyte present in the bulk phase, surface rheological properties upon addition of Ce(NO) and Yb(NO) were determined. In order to account for the surface activity of the nitrate ion, comparative measurements using NaNO were carried out additionally.

The surface rheological signature of the geometric isomers of an azobenzene-surfactant.

The equilibrium and dynamic surface properties of a photosensitive azobenzene-surfactant subject to illumination with UV and Vis-light leading to the respective geometric cis- and trans-isomers were studied. The adsorption layers formed by the soluble surfactant were characterized by pendant drop tensiometry and surface rheology using the oscillating bubble technique. Aqueous solutions corresponding to the geometric isomers could clearly be distinguished in terms of both their equilibrium and dynamic surface properties.

Measurement of the lifetime of individual foam lamellae.

Foams play a crucial role in a number of practical applications. Their analysis in terms of stability is subject to a large number of parameters. An automated, light reflection based device for the measurement of the lifetime of a single foam lamella of aqueous surfactant solutions in contact with the liquid and gas phases is proposed.

The Role of Surface Viscosity in the Escape Mechanism of the Stenus Beetle.

Beetles of the species Stenus comma live and hunt close to ponds and rivers, where they occasionally fall on the water surface. To escape this jeopardized state, the beetle developed a strategy relying on the excretion of a secretion containing the substances stenusine and norstenusine. They reduce surface tension and propel the bug to the saving river bank.

Retrieval of complex χ((2)) parts for quantitative analysis of sum-frequency generation intensity spectra.

Vibrational sum-frequency generation (SFG) spectroscopy has become an established technique for in situ surface analysis. While spectral recording procedures and hardware have been optimized, unique data analysis routines have yet to be established. The SFG intensity is related to probing geometries and properties of the system under investigation such as the absolute square of the second-order susceptibility χ((2)) (2).

Impact of the imaginary part of the surface dilatational modulus on the splashing behavior of drops.

The relation between the complex surface dilatational modulus E of aqueous surfactant solutions and the splashing behavior of their drops on liquid surfaces was investigated. The surface dilatational modulus E of selected surfactant systems has been determined in the frequency range of 3 to 500 Hz by means of the oscillating bubble technique. According to the functional dependence of the phase ϕ of the complex modulus E(ω, c)exp[iϕ(ω, c)] at higher frequencies, adsorption layers can be classified as surface elastic or surface viscoelastic.