Steam-assisted gravity drainage processes for heavy oil recovery produce extremely stable nanoemulsions that remain dispersed in water for years if left untreated. The need to produce clean water for recycling demands that the nanoemulsions be destabilized and the oil phase separated from the water. The destabilization of these nanoemulsions requires an understanding of the nature of the oil-water interface. In this paper, the zeta potential and sizes of the nanoemulsions were measured with and without treatment with a cationic polymer. The coalescence of nanoemulsions was monitored by size changes using dynamic light scattering, microscopy, and water-phase separation kinetics. Small-deformation pendant drop oscillation was used to measure the dilational viscoelasticity of the oil-water interface with and without polymer adsorption. The results indicated that both the size and the large negative zeta potential contribute to the stability of the nanoemulsions in water. The addition of polymer not only causes charge neutralization but also enhances the interfacial activity and modifies the interfacial dilational viscoelasticity. The viscoelasticity is dependent on the frequency of droplet oscillation. Polymer adsorption modifies these interfacial properties while enabling coalescence and phase separation.