The spinning drop video tensiometers of the SVT series are special-purpose optical instruments for measuring extremely low interfacial tensions and rheological properties. This measuring technique offers unrivaled possibilities for the analysis of surfactant effectiveness in the development of emulsions or in the enhanced oil recovery.
Spinning drop tensiometry is the technology of choice for measuring extremely small interfacial tensions. The method is based on the optical contour analysis of a drop. This drop, instead of hanging from a dosing needle and being exposed to gravitation, is located inside of a rotating capillary.
Inside of the capillary, the centrifugal force pushes the denser liquid surrounding the drop outwards while the less dense drop gets pushed towards the rotational axis. Hence the drop is deformed cylindrically and its interfacial area increases. The interfacial tension counteracts this area increase and thus can be determined by analyzing the equilibrium drop shape.
Ultra-low interfacial tensions occur particularly in microemulsions that are used, for example, in enhanced oil recovery. At suitable conditions, microemulsions form spontaneously from water, oil, and surfactant. The thermal stability of the microemulsion plays a crucial role as temperatures in the oil reservoir can reach well beyond the boiling point of water. Thus, measurements with superheated aqueous solutions of up to 130 °C are an important step in the research of appropriate surfactants and mixture compositions.
With spinning drop tensiometry it is also possible to analyze how an interface reacts when its area is enlarged or reduced (interfacial rheology). For example, how fast can surfactants from the bulk adsorb at the interface in order to stabilize a newly formed emulsion? To investigate such questions the rotational velocity is varied in a spinning drop experiment, typically in an oscillating manner, which directly results in a change of size of the interfacial area.
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