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Physical Chemistry / Molecular Material ScienceThin Film Pressure Balance

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Thin Film Pressure Balance

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Thin Film Pressure Balance
Thin Film Pressure Balance
Lupe

The stability of foam films and the vertical interactions between film surfaces can be determined in a so-called thin film pressure balance (TFPB). Both, equilibrium (disjoining pressure vs. film thickness) and dynamic film thinning (film thickness vs. time) measurements can be done.

Disjoining pressure isotherms give information about the forces acting between approaching interfaces while dynamic measurements probe the kinetic of film drainage (thinning velocity, film transitions). Usually, this apparatus is used for disjoining pressure measurements of free-standing foam films (air/liquid/air). In recent studies we could show that this method can also be applied to wetting films (air/liquid/solid). Disjoining pressure isotherms are measured with the porous plate technique 2,3,4. In this case the film holder consists of a porous glass disc. This ensures free drainage of the foam film lamella. The film itself is formed within in a small hole of 1 mm in diameter in the middle of this porous disc. The specimen holder is placed in a sealed chamber. This set up allows to adjust a constant excess pressure. Variation of the applied external pressure allows a wide-range adjustment of film thickness. The thickness is measured interferometrically. The film can be monitored with video microscopy.

 

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