Biomedical subjects

AJ Fillery-Travis

Publications and source records attributed to AJ Fillery-Travis.

3 recordsLinked to original sources

PubMed2000

Characterization of a Polydisperse Depletion-Flocculated Emulsion.

The addition of nonadsorbing polymer to an alkane-in-water emulsion causes the droplets to flocculate into a space-spanning, stress-bearing network. We report rheological measurements of an emulsion of 1-bromohexadecane-in-water flocculated by hydroxy-ethylcellulose. Small-deformation oscillatory measurements allowed characterization of the structure during formation and an indication of the strength of the resulting network. Emulsions without polymer, and polymer solutions alone, showed essentially viscous behavior, with dominant viscous modulus over the whole frequency range (0.01-10 Hz). However, the emulsion containing polymer demonstrated a significant elastic modulus, dependent on the oil and polymer concentrations, attributable to interdroplet depletion interactions. Power-law relationships were observed between the elastic modulus, elastic strain limit, and oil volume fraction, but the indices were lower than those predicted by fractal models, giving unrealistic fractal dimensionalities. The modulus increased exponentially with polymer concentration, but the elastic strain limit was independent of added polymer. The rate of formation of the network was not consistent with diffusion-controlled aggregation. Copyright 2000 Academic Press.

Journal Article↗

PubMed1998

I. Creaming Behavior.

We report an experimental investigation on the creaming behavior of flocculated, polydisperse, oil-in-water emulsions. Flocculation is by addition of a depletion flocculant, the polymer hydroxyethylcellulose (HEC), at a range of concentrations. The creaming behavior is dependent on the oil volume fraction and polymer concentration. At low concentrations of HEC, the droplets cream either individually or in two populations, a flocculated phase, and a coexistent phase of individual droplets. At higher HEC concentrations, the droplets appear to cream as a single entity, with a sharp lower boundary, separating the region with droplets from a clear serum at the base of the container. In these emulsions, and in some of the coexistent ones, there is a significant delay before creaming starts. Once started they cream at a constant rate. We have identified the continuous phase viscosity as a major factor. The aim of this work is to elucidate the mechanisms underlying the delay before creaming. We propose that as soon as they flocculate, the emulsions form space-filling structures, which slowly rearrange until channels are formed that allow the flow of bulk continuous phase to the base of the container. Scaling arguments are presented that suggest the delay could be related to the single-droplet diffusion rate. Copyright 1998 Academic Press.

Journal Article↗

PubMed1998

II. Steady-State Rheological Investigations.

Depletion flocculation of an alkane-in-water emulsion has previously been found to induce phase separation and, above certain polymer and oil concentrations, a delay period prior to the onset of creaming. In this paper the steady-state viscometry of an emulsion of 1-bromohexadecane-in-water has been investigated in the presence of hydroxyethylcellulose as the depletion flocculant. We have sought to characterize the flow 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, characterized the delay period by reference to the behavior of a related system, differing only in oil composition. At oil and polymer concentrations conducive to the presence of a delay period, the emulsions were found to be shear thinning, whereas the emulsion system in the absence of polymer and the isolated continuous phases were Newtonian. The structure formation influencing the rheology of the emulsions at high polymer concentrations was attributed entirely to interdroplet depletion interactions. The concept of dynamic yield stress for such a system is discussed and the consequences for the structure of a buoyancy-resisting space-spanning phase or "transient gel." Copyright 1998 Academic Press.

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