RHEOLOGICAL PHENOMENA OCCURRING DURING THE SHEARING FLOW OF MAYONNAISE

A rheometrical study reveals that mayonnaise exhibits apparent wall sl ip in both small amplitude oscillatory shear flow and torsional flow. Whereas in the case of small amplitude oscillatory shear classical tec hniques are applicable for extracting bulk material properties, this i s not the case for torsional flow. Progressively increasing the shear stress in torsional flow manifests another flow phenomenon that domina tes the slip process. It is argued that ''particles'' within the mayon naise migrate radially towards the center of the geometry. Spectroscop ic techniques are employed to confirm that, following an experiment, m aterial at the rim of the geometry differs from that towards the cente r. Experiments performed in a cone-and-plate geometry yield results th at are qualitatively similar to those obtained in torsional flow tests thus indicating that the migration is not due solely to the radial sh eer-rate gradient that is present in torsional flow. (C) 1998 The Soci ety of Rheology. [S0148-6055(98)00206-5].