Figure 14—Surfactant induced fingering stability.
Ostwald ripening also occurred in the high viscosity case (polymer-induced) where surfactant- induced fingers were consumed by the larger-sized polymer fingers as the surfactant induced fingers lost their hydrodynamic stability (Figure 15 ). Polymer-induced hydrodynamic stability then dominated the overall finger morphology rendering the number of droplets zero. Polymer-induced fingers are also observed to follow the original finger patterns of the surfactant-induced fingers however, as they consumed and developed into new morphologies. In our previous study (Lee et al. 2020), polymeric nanofluid (cellulose nanocrystals) was also observed to demonstrate a similar behavior and such effect became more pronounced as the viscosity of the solution increased over time (increase in hydrostatic stability).