Tailings Pond Surfactant Analogues: Effects on Toluene-Diluted Bitumen Drops in NaHCO3/K2CO3 Solution. Part 2: Dilational Interfacial Viscoelasticity
2013
Angle, Chandra W. | Hua, Yujuan
In this two-part work, we used dilational interfacial rheometry to study the interfaces associated with diluted bitumen in simulated pond water as a function of pH, for three different surfactants: two simple carboxylic acids, one with a straight chain and one having a ring in the tail, and the more complex sodium naphthenates. In part 1 (10.1021/ef400376v), dynamic interfacial tension as a function of time was used to measure adsorption. In part 2, described in the present paper, interfacial dilational rheology was studied as a function of oscillation frequency for three different concentrations of the three surfactants adsorbed at the interface between buffer and toluene-diluted bitumen. The concentrations used were selected on the basis of results from part 1 (10.1021/ef400376v). Our results show that interfacial viscoelasticity depends upon not only the tail complexity in the surfactants but also the surfactant concentration and buffer pH. The adsorbed naphthenates were synergistic with interfacially active materials indigenous to bitumen, resulting in high interfacial rigidity (reduced interfacial elasticity). The simpler carboxylic surfactants were less effective. The observed interactions provide insight into possible transport pathways for surfactants in pond water when bitumen is present.
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