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SVT – Spinning Drop Tensiometer

SVT – Spinning drop video tensiometer

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 unrivalled possibilities for the analysis of surfactant effectiveness in the development of emulsions or in the enhanced oil recovery. In the following you will learn about the possibilities that the spinning drop tensiometry offers and about our SVT 25 with its accessories and intuitive software control.

Spinning Drop Tensiometry 

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 analysing the equilibrium drop shape.

Vonnegut evaluation 

An easy and established evaluation method for strongly elongated drops is the interfacial tension calculation by Vonnegut. Here the shape that the drop adopts at rotation with the angular velocity ω is approximated by a cylinder. The cylinder has a rotational energy that decreases with decreasing radius, which compensates the increase in interfacial energy due to increasing elongation and interfacial area. In the equilibrium state an energy minimum is reached. Vonnegut equation:

Enhanced oil recovery (EOR)

Ultra-low interfacial tensions occur particularly in microemulsions which 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.

Interfacial rheology

With spinning drop tensiometry it is also possible to analyse 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 stabilise 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.

SVT 25

The Spinning drop video tensiometer SVT 25 is a compact optical measuring instrument for the determination of low to ultra-low interfacial tensions and rheological interface properties.

SVT Accessories

Due to the modular design philosophy the SVT models can be combined with different temperature controlled measuring cells and various capillaries.

SVT Software

The SVT Software supports specifying measurement procedures and collecting and evaluating data. The software is designed  for the use under Microsoft Windows®.

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