spinningdrop

Spinningdrop is a measurement technique and apparatus used in interfacial science to quantify the interfacial tension between two immiscible liquids by manipulating a droplet that is spun inside a surrounding liquid within a capillary. The method is commonly implemented as a spinning drop tensiometer and is widely used in polymer science, petroleum chemistry, and emulsion research.

Principle and setup: A droplet is formed at the tip of a capillary and immersed in a continuous immiscible phase. The capillary is mounted on a rotational mechanism and the system is brought to a controlled angular velocity. Rotation generates centrifugal forces that elongate the droplet along the axis of rotation. At a given velocity, the drop reaches a steady elongated shape whose geometry depends on the interfacial tension, the densities, and the viscosities of the two liquids. By recording the drop profile and applying established theoretical relations, the interfacial tension between the liquids can be determined. The apparatus typically includes temperature control, precision imaging, and calibration procedures.

Applications and considerations: Spinningdrop is valued for its low sample consumption and high sensitivity, making it suitable for measuring very low interfacial tensions and for systems where conventional methods are impractical. It is commonly applied to oil–water, polymer blends, surfactant solutions, and complex colloidal systems. Careful calibration, control of impurities, and accurate knowledge of densities and temperatures are important for reliable results. Limitations include the requirement that the liquids form a stable droplet under rotation and that the method may be sensitive to contamination and capillary geometry.

See also: pendant drop method, Wilhelmy plate method, interfacial tension.