Scientists Explore Upper Limit of Viscosity

A recent study by researchers at ETH Zurich and the University of Cambridge has identified a potential upper boundary for viscosity, a critical property governing material flow, challenging assumptions about the behavior of highly viscous substances. While viscosity has been extensively characterized in fluids like water and lava, the question of whether viscosity can theoretically reach a maximum has remained unresolved. The team analyzed a range of materials, including metallic glasses, supercooled melts, and polymer solutions, using computational simulations and experimental data to determine a viscosity threshold around 10^22 pascal-seconds. This value, they propose, represents a physical limit where molecular or atomic interactions become so restricted that further increases in viscosity lose practical meaning.

The findings, published in *Nature Materials*, bridge gaps between material science, geophysics, and industrial applications. By establishing this threshold, the research clarifies the behavior of extremely viscous systems, such as the Earth’s deep mantle or industrial glass-forming processes, where viscosity influences structural stability and flow dynamics. The study also highlights how viscosity transitions from fluid-like to solid-like behavior as materials approach this limit, offering insights into phenomena like volcanic rock solidification and the formation of amorphous solids. Researchers emphasize that the threshold is not an absolute barrier but a point where conventional viscosity measurements become less applicable, necessitating new frameworks to describe material behavior.

This work underscores the importance of redefining fundamental material properties in extreme conditions. By setting a benchmark for viscosity, the study provides a foundation for advancing models in geodynamics, material design, and planetary science. The researchers note that further experiments on exotic materials, such as those found in planetary interiors, could refine the threshold and expand its applicability. As industries and geoscientists increasingly rely on precise viscosity data, this research offers a critical reference point for understanding the boundaries of material flow.