Simple Liquids Can Fracture Like Solids, Drexel Researchers Discover

Researchers at Drexel University have reported that simple liquids can fracture like solid objects under specific conditions. This discovery, published in "Physical Review Letters", indicates that viscous liquids can break if stretched with sufficient force, suggesting a more prominent role for viscosity in a liquid's mechanical properties than previously understood.

According to Thamires Lima, an assistant research professor at Drexel's College of Engineering, liquids will reach a point of "critical stress" where they fracture like a solid when pulled apart with enough force per area. This phenomenon is believed to apply to all simple liquids, including water and oil.

Discovery Details

The unexpected observation occurred during extensional rheology tests, which measure the force required to make a liquid flow. Researchers noticed that tar-like liquids separated with a sudden snap rather than exhibiting typical thinning behavior. High-speed camera footage showed a behavior similar to brittle fracture in solid materials, a phenomenon not previously observed in simple liquids.

Critical Stress and Viscosity

The initial liquids observed fracturing were tar-like hydrocarbon blends, which fractured at a critical stress of 2 megaPascals. Subsequent tests with styrene oligomer, a simple liquid with similar viscosity, showed fracturing at the same stretching rate.

Further experiments at varying temperatures, which altered viscosity, revealed that each viscosity level had a unique stretching rate that induced fracturing, always proportional to the 2 megaPascal critical stress point. This indicates viscosity plays a key role in the solid-like fracturing behavior.

Implications for Fluid Dynamics

Historically, fracturing has been associated with elasticity, a material's ability to store stress. Simple liquids, in their liquid state, typically lack a dominant elastic mechanism and flow rather than break.

This new finding challenges the previous understanding that fracturing is restricted to elastic materials. The team's comparison of oligomer styrene liquid to its polymer liquid counterpart suggested that elasticity does not play a role in simple liquid fracture, as both broke at similar critical stress points. This implies the phenomenon may be broadly applicable across various liquids.

Future Research

The research team plans to continue investigating the physical mechanisms behind liquid fracture, with early indications suggesting a potential link to cavitation. Understanding this phenomenon could have significant applications in areas like hydraulics, 3D printing, and fiber spinning.