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SYPF: Physics of Foams

SYPF 2: Foams II

SYPF 2.4: Vortrag

Mittwoch, 10. März 2004, 15:30–15:50, H16

Foam Analysis by the Foam Pressure Drop Technique — •R. Miller¹, C. Stubenrauch², Khr. Khristov³, L. Christov³, A.V. Makievski⁴, and D. Exerowa³ — ¹MPI für Kolloid- und Grenzflchenforschung, Am Mühlenberg 1, D-14476 Golm, Germany — ²Institute Phys. Chem., University Cologne, Luxemburger Str. 116, D-50939 Cologne, Germany — ³Institute of Physical Chemistry, Bulgarian Academy of Sciences, Sofia 1113, Bulgaria — ⁴SINTERFACE Technologies, Volmer Str. 5-7, D-12489 Berlin, Germany

Foam is a complex capillary system and the processes of foam drainage and foam destruction (stability) are important for its properties. These processes are interrelated in a very peculiar way. The questions on which would be the predominating mechanism or how would the processes impact on each other depend entirely on the characteristics of the foam. The complex relationships make it very hard to assess the different processes independently. Moreover, for many application the drainage is important, for example in firefighting, food industry, while for others the lifetime (stability) plays the major role, such as in foam concentration, foam separation.

The characterisation of foams by the foam pressure drop technique gives access to the main properties of aqueous foams in a reasonably short time even if the foam is very stable. This technique determines the decrease of the water content W as a function of time t (drainage) and the lifetime τ_p of a foam at a definite reduced pressure P_r (pressure drop). It is found that the rate of drainage is influenced by the type of foam film, namely Common Thin Film (CTF), Common Black Film (CBF), Newton Black Film (NBF), and Bilayer Film (BF). The type of film the foam consists of also plays a role for the lifetime τ_p. Measuring τ_p as a function of Δ P one obtains characteristic curves for foams consisting of CTFs, CBFs, NBFs, and BFs, respectively.

Example experiments are given for some surfactant solutions and discussed with respect to the correlation between single foam films and macroscopic foams. The properties of selected foam films will also be discussed with respect to the dynamic and mechanical properties of the respective adsorption layers. This attempt demonstrates one of the basic open questions – what are the interrelations between the properties of adsorption layers and respective isolated liquid foam films with the properties of the final foam.