New insights on the complex dynamics of two-phase flow in porous media under intermediate-wet conditions

Multiphase flow in porous media is important in a number of environmental and industrial applications such as soil remediation, CO2 sequestration, and enhanced oil recovery. Wetting properties control flow of immiscible fluids in porous media and fluids distribution in the pore space. In contrast to the strong and weak wet conditions, pore-scale physics of immiscible displacement under intermediate-wet conditions is less understood. This study reports the results of a series of two-dimensional high-resolution direct numerical simulations with the aim of understanding the pore-scale dynamics of two-phase immiscible fluid flow under intermediate-wet conditions. Our results show that for intermediate-wet porous media, pore geometry has a strong influence on interface dynamics, leading to co-existence of concave and convex interfaces. Intermediate wettability leads to various interfacial movements which are not identified under imbibition or drainage conditions. These pore-scale events significantly influence macro-scale flow behaviour causing the counter-intuitive decline in recovery of the defending fluid from weak imbibition to intermediate-wet conditions

The Race of Nanowires: Morphological Instabilities and a Control Strategy

The incomplete growth of nanowires that are synthesized by template-assisted electrodeposition presents a major challenge for nanowire-based devices targeting energy and electronic applications. In template-assisted electrodeposition, the growth of nanowires in the pores of the template is complex and unstable. Here we show theoretically and experimentally that the dynamics of this process is diffusion-limited, which results in a morphological instability driven by a race among nanowires. Moreover, we use our findings to devise a method to control the growth instability. By introducing a temperature gradient across the porous template, we manipulate ion diffusion in the pores, so that we can reduce the growth instability. This strategy significantly increases the length of nanowires. In addition to shedding light on a key nanotechnology, our results may provide fundamental insights into a variety of interfacial growth processes in materials science such as crystal growth and tissue growth in scaffolds