Energy-minimized mobilization of trapped non-aqueous phase liquids ganglia in three-dimensional biconical pores: Insights from surface evolver simulations

The mobilization of a ganglion is of great significance in various domains, including soil contamination. For effective soil remediation, it is essential to correctly characterize the behavior of trapped nonaqueous phase liquids (NAPLs). Therefore, in this study, a biconical pore structure is employed to investigate the conditions of mobilization of a trapped NAPL ganglion using Surface Evolver software. The results showed that in the three-dimensional model, the ganglion can take a sequence of saddle-shapes of increasingly negative mean curvature as it approaches the middle of the pore, and depending on the contact angle, it can cross the bulge through two main mechanisms: an asymmetric jump and an asymmetric crawl. These behaviors are triggered by the fact that the ganglion seeks the path of low energy. The pressure difference is observed to decrease with pore occupancy (from n = 2 to n = 2.5) and then increase (to n = 2.75). The same behavior occurs for pore occupancy n + 1; thus, pore occupancy plays a significant role only within a single pore. For a ganglion occupying the whole pore, the critical pressure is symmetric about the neutral wettability, namely, θ = 90°. For the pores partially occupied by the ganglion, the wettability condition of the pore wall can favor ganglion mobilization depending on pore occupancy. Furthermore, the contact angle hysteresis leads to a considerable increase in resistance to ganglion mobilization. These insights provide a deeper understanding of the pore-scale dynamics involved in NAPL mobilization, informing the design of more effective remediation strategies.