Despite the clear benefits of High Float (HF) emulsions, current formulations are not optimized. The design of "next generation" emulsions will require knowledge of the basic science that underlies HF systems. At present, the understanding of HF emulsions is rudimentary in two regards: 1. No rheological model is available to predict the flow/deformation of HF materials. The only semiquantitative characterization is whether the breakthrough time in a float test would exceed 20 minutes. 2. The mechanism(s) by which the stabilizer (tall oil soap) gives rise to the unique rheology of HF residues is not understood. This paper reports a detailed study of the rheology of HF residues. The most notable feature of this material is its yield stress, which can be quantified using a stress-ramp procedure. A rheological model -a hybrid between Bingham fluid and Kelvin-type solid - is developed to predict the ramp response of the residue material. It is proposed that the yield stress, rather than the breakthrough time in float tests, should be the metric for characterizing HF residues and other similar materials. In addition to rheological studies, we speculate also on the microstructure of the HF residue, and how it leads to the material's macroscopic behaviour.
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