Biconical Bob Oscillatory Interfacial Rheometer

Abstract

This paper describes a biconical bob oscillatory interfacial rheometer designed to measure the dynamic viscoelastic response of a liquid–liquid interface subjected to a small amplitude oscillatory shear stress. This instrument is used to examine the rheological behavior of interfaces in the presence of surfactants, especially macromolecular types. Rheological parameters are calculated from a hydrodynamic analysis incorporating a linear viscoelastic interfacial rheological model. The general response of this instrument is compared with the oscillatory deep channel interfacial rheometer which is also capable of similar measurements. Measurements of interfacial viscoelasticity for the same liquid–liquid system with the two rheometers, the biconical bob and the deep channel rheometers, are shown to be comparable. This study demonstrates the intrinsic nature and, therefore, the instrument independence of these dynamic interfacial rheological properties. Accurate measurements of interfacial shear viscoelasticity can be carried out over a wide range of systems by combining measurements with the oscillatory interfacial rheometers. The limitations and regime of usefulness of these instruments are discussed.