BICONICAL BOB OSCILLATORY INTERFACIAL RHEOMETER

This paper describes a biconical bob oscillatory interfacial rheometer designed to measure the dynamic viscoelastic response of a liquid-liq uid interface subjected to a small amplitude oscillatory shear stress. This instrument is used to examine the rheological behavior of interf aces in the presence of surfactants, especially macromolecular types. Rheological parameters are calculated from a hydrodynamic analysis inc orporating a linear viscoelastic interfacial rheological model. The ge neral response of this instrument is compared with the oscillatory dee p channel interfacial rheometer which is also capable of similar measu rements. Measurements of interfacial viscoelasticity for the same liqu id-liquid system with the two rheometers, the biconical bob and the de ep channel rheometers, are shown to be comparable. This study demonstr ates the intrinsic nature and, therefore, the instrument independence of these dynamic interfacial rheological properties. Accurate measurem ents of interfacial shear viscoelasticity can be carried out over a wi de range of systems by combining measurements with the oscillatory int erfacial rheometers. The limitations and regime of usefulness of these instruments are discussed, (C) 1998 Academic Press.