CHARACTERIZATION OF A DEPLETION-FLOCCULATED POLYDISPERSE EMULSION II - STEADY-STATE RHEOLOGICAL INVESTIGATIONS

Depletion flocculation of an alkane-in-water emulsion has previously b een found to induce phase separation and, above certain polymer and oi l concentrations, a delay period prior to the onset of creaming. In th is paper the steady-state viscometry of an emulsion of 1-bromohexadeca ne-in-water has been investigated in the presence of hydroxyethylcellu lose as the depletion flocculant. We have sought to characterize the f low behavior of this emulsion system and determine the characteristic rheology during the delay period. The use of this near-density-matched system eliminates the effect of creaming, and we have, therefore, cha racterized the delay period by reference to the behavior of a related system, differing only in oil composition. At oil and polymer concentr ations conducive to the presence of a delay period, the emulsions were found to be shear thinning, whereas the emulsion system in the absenc e of polymer and the isolated continuous phases were Newtonian. The st ructure formation influencing the rheology of the emulsions at high po lymer concentrations was attributed entirely to interdroplet depletion interactions. The concept of dynamic yield stress for such a system i s discussed and the consequences for the structure of a buoyancy-resis ting space-spanning phase or ''transient gel.'' (C) 1998 Academic Pres s.