Stability, transport and applications of polyaphrons in porous media
Polyaphrons are a kind of macroemulsion. The most distinctive feature of polyaphrons is their high stability. On the other hand, certain polyaphrons can be effectively destabilized by multivalent ions. In this dissertation, we devise a novel procedure that utilizes the fact that polyaphrons can be destabilized by certain ions to deliver light chemicals to lower the density of dense non-aqueous phase liquid (DNAPL) contaminants in situ. We first investigate how the stability of diluted polyaphrons is affected by the properties of the continuous phase. We find that polyaphrons can be destabilized by a low concentration of Al3+ or Ca2+ in the continuous phase while the cations have a stabilizing effect at high concentrations. Our results suggest that upon dilution polyaphrons may experience a structure transition, i.e. from bilayer structure to mixed monolayer structure. We examine the efficiency of our novel procedure on removing 1,2-dichlorobenzene (DCB) from a sand column. The results show that our procedure effectively prevents downward migration of DCB during surfactant flooding. Depending on the injection strategy and initial distribution of DCB, as mush as 97% of the DCB entrapped in the sand column is removed, most of which is in a bulk organic phase lighter than water. Since the coalescence between aphrons is a crucial step in the polyaphron treatment, we develop a boundary element method (BEM) model to study the coalescence behavior of a pair of drops of equal size in a constricted tube. Our simulations show that the capillary number Ca plays an important role in determining whether the drops coalesce. At low Ca, drops hardly deform and coalescence occurs at the entrance of the pore throat, whereas significant deformation enables the drops move through the pore without coalescence at high Ca. Coalescence is favored at intermediate values of the viscosity ratio. The destabilizing effect of added electrolytes is found to be insignificant for the drop interaction for 10 micron-size drops, but significant for micron-size drops. Among the geometric-related parameters, the drop/pore size ratio appears to be the most significant: coalescence does not occur when this ratio is equal to or below unity.
emulsion stability, DNAPL remediation, boundary element method, drop coalescence, porous media, polyaphrons
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