Instabilities at fluid-fluid interfaces are ubiquitous in porous media, even at small flow rates. The growth of fluid fingers during fluid-fluid immiscible displacement in a porous medium results in partial saturation of the medium, and inefficiency in displacement has a tremendous economic impact on oil recovery, chemical reactors, and water filtration industries. In this study, we demonstrate that an inherent asymmetry in the structure of a porous medium controls the development of fluid fingers due to instabilities at fluid interfaces. We construct a 2D porous medium consisting of a matrix of triangles using soft lithography to investigate air displacement by water. Utilizing optical microscopy and precise control of the injection pressure, we illustrate that the direction of injection with respect to the orientation of the triangles (apex vs. base) dictates the development of fluid fingers at the interface. At a critical injection pressure, we observe a uniform displacement of air in the apex direction. In contrast, a distinct fluid finger grows when injecting water in the opposite direction (base of the triangle). In this research, we demonstrate that the asymmetry of a porous medium controls the first-order instability at air-water interfaces, leading to the development of fluid fingers.

Publication Date


Document Type


Student Type


Degree Name

Materials Science and Engineering (MS)

Department, Program, or Center

Physics and Astronomy, School of


College of Science


Shima Parsa

Advisor/Committee Member

Pratik Dholabhai

Advisor/Committee Member

Jairo Diaz


RIT – Main Campus