Adhesives have poor bonding properties on aluminum. Aluminum alloys are therefore pretreated in conversion baths in order to prepare them for bonding. Such pretreatment methods are increasing in importance, particularly in vehicle construction. A current method is immersion bath treatment with the active substances hexafluorotitanic or hexafluorozirconic acid. The process parameters exposure time, temperature and concentration have a great influence on the surface free energy and its polar and disperse parts – quantities that are closely linked to the wetting and adhesion behavior of the surface and which therefore greatly influence the adhesive strength and the ageing behavior of the bonded joint. The Austrian Research Institute ofi has carried out a publicly funded study on the pretreatment of aluminum alloys in which KRÜSS participated. In addition to measurements of the adhesive strength and ageing behavior, contact angle measurements were made in order to investigate the effect of the bath parameters exposure time and temperature on the surface free energy and its polar and disperse parts.

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Interfacial rheology describes the change of the surface and interfacial tension, and surfactant adsorption, upon surface area variations, like those encountered in sheared foams and emulsions. There are several methods allowing a controllable deformation and simultaneous measurement of the surface tension; however, all of them are not directly applicable to high-viscosity systems. This article describes successful surface rheology measurements at the interface between aqueous surfactant solutions and silicone oils with differing viscosities (5 to 10,000 mPas) using a pressure detection tensiometry and oscillating spherical drops.

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