Princeton researchers have solved a 54-year-old puzzle about why certain fluids strangely slow down under pressure when flowing through porous materials, such as soils and sedimentary rocks. The findings could help improve many important processes in energy, environmental and industrial sectors, from oil recovery to groundwater remediation.

The fluids in question are called polymer solutions. These solutions — everyday examples of which include cosmetic creams and the mucus in our noses — contain dissolved polymers, or materials made of large molecules with many repeating subunits. Typically, when they’re put under pressure, polymer solutions become less viscous and flow faster. But when going through materials with lots of tiny holes and channels, the solutions tend to become more viscous and gunky, reducing their flow rates.

To get at the root of the problem, the Princeton researchers devised an innovative experiment using a see-through porous medium made of tiny glass beads — a transparent artificial rock. This lucid medium allowed the researchers to visualize a polymer solution’s movement. The experiment revealed that the long-baffling increase in viscosity in porous media happens because the polymer solution’s flow becomes chaotic, much like turbulent air on an airplane ride, swirling into itself and gumming up the works.
https://scitechdaily.com/fractured-artificial-rock-helps-crack-a-strange-54-year-old-fluid-mystery/