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New Developments 1/1/17

A new generation of bubble pressure tensiometers, including BPA-2P and BPA-2S , as follow up developments of the excellent predecessors BPA-1P and BPA-1S , are available more...


New Books 1/1/17

Textbook “Dispersionseigenschaften - Stabilität, 2D-Rheologie, 3D-Rheologie“ This textbook contains the main fundamental knowledge on interfaces, colloidal systems more...


Latest events 1/1/17

2D-3D Rheology and Stability of Disperse Systems - User Workshop, May 8-10, 2017, Berlin-Schönefeld, Germany In May 2017 the 2D-3D Rheology and Stability of Disperse more...

Interfacial Dilational Rheology



A typical dilational experiment can be carried out with the drop shape tensiometers PAT. Using the dosing system the drop area can be subjected to transient or harmonic perturbations:

PAT1M  PAT2S

Both instruments provide the opportunity to change the size of a drop or bubbles according to a given time line. This can include harmonic perturbations and various types of transient area changes, such as ramps, jumps, and combinations of them. For harmonic perturbations, frequencies are rather limited, as at too high frequencies the drop profiles deviate from a Laplacian shape and therefore the main condition of the methodology is no longer fulfilled. A clear indication for being beyond the physical limit in an oscillation experiment is the standard deviation as measure for the quality of fitting the experimental drop profile. As soon as these values of the standard deviation become much larger than those observed at constant drop size the chosen frequency is out of the acceptable limits.

Oszillating Drop and Bubble Analyzer ODBA1M

The use of small spherical drops allows oscillation at much higher frequencies as it is accessible with the PAT technique. This is true due to decreased impact of inertia on the drop oscillation modes, which are expected to oscillate in a more or less radial way. As soon as additional (wobbling) modes come into play, the limits of this technique are reached. Unfortunately, there is not a single control parameter available as in PAT measurements to test the physically reasonable frequency limit. Only a general trend can be clearly seen: the smaller the drop and the smaller the amplitudes of oscillation are, the higher are the frequencies for physically reasonable experiments. A real test of this frequency limit would require experiments with liquid systems in absence of any surface active molecules, including possible impurities in the studied liquids.