Rheological measurements biconical rheometer

FIG. 4.22 Schematic of biconical tool for surface rheology measurements using the Paar Physica interfacial rheometer. (Courtesy of American Institute of Physics.)... 

For interfacial shear rheology measurements, an interfacial shear rheometer (MCR301, Anton Paar, Ostfildem, Germany) was used equipped with a biconical disc geometry as described in Riihs et al. [60]. For all interfacial experiments, MCT oil was used as the oil phase. Surface-active constituents were removed from the oil through adsorption onto solid particles. The absence was confirmed through measurement of the interfacial tension. 

Wasan and his research group focused on the field of interfacial rheology during the past three decades [15]. They developed novel instruments, such as oscillatory deep-channel interfacial viscometer [20,21,28] and biconical bob oscillatory interfacial rheometer [29] for interfacial shear measurement and the maximum bubble-pressure method [15,29,30] and the controlled drop tensiometer [1,31] for interfacial dilatational measurement, to resolve complex interfacial flow behavior in dynamic stress conditions [1,15,27,32-35]. Their research has clearly demonstrated the importance of interfacial rheology in the coalescence process of emulsions and foams. In connection with the maximum bubble-pressure method, it has been used in the BLM system to access the properties of lipid bilayers formed from a variety of surfactants [17,28,36]. 

In 1983, Steinbom and Flock studied the rheology of crude oils and water-in-oil emulsions (58). Emulsions with high proportions of water exhibited pseudoplastic behavior and were only slightly time dependent at higher shear rates. Omar et al. also measured the rheological characteristics of Saudi crude oil emulsions (59). NonNewtonian emulsions exhibit pseudoplastic behavior and followed a power-law model. Mohammed et al. studied crude oil emulsions using a biconical bob rheometer suspended at the interface (60). More stable emulsions displayed viscoelastic behavior and a solid-like interface. Demulsifiers changed the solid-like interface into a liquid one. 

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