Just when it seems we grasp the universe’s structure, physics throws another surprise our way. Researchers have found that simple liquids possess breaking points beyond which they suddenly fracture like solids. The study’s findings are detailed in the journal Physical Review Letters.
This discovery carries significant implications for fluid mechanics. If liquids can not only stretch and flow but also break apart, this has relevance across domains, from 3D printing technologies to the biological systems within our bodies.
The unexpected finding emerged from experiments conducted by researchers at Drexel University in the US and ExxonMobil, who were studying how viscous liquids respond to intense forces. Initially, they suspected the lab equipment itself had malfunctioned.
“There was a very loud crack from a fracture that genuinely startled me,” stated chemical engineer Thamires Lima from Drexel University.
The research team confirmed they replicated the experiments multiple times to ensure the results were reliable.
“What we observed was completely surprising,” remarked Nicholas Alvarez, also a chemical engineer at Drexel University. “Once this phenomenon was verified, the research evolved into an entirely different scientific endeavor.”
The experimental setup involved placing the liquids between two metal plates, monitored by a high-speed camera, while various forces were applied to the setup. The initial snap occurred when the liquid was stretched with a force comparable to suspending a bag of bricks across a fingernail-sized area.
This behavior was seen in a resin-like hydrocarbon mixture, and the identical rupture point was later observed in another fluid—styrene oligomer. This substance was also thick and resinous, leading the researchers to believe that viscosity (the liquid’s resistance to flow) plays a crucial role.
Stresses accumulate differently in thicker, more viscous liquids compared to thinner, less viscous ones. Based on these tests, it was determined that denser liquids might fracture even with slower stretching, yet the requisite force appears consistent regardless of the viscosity level.
While it was previously known that liquids could fracture when sufficiently cooled or agitated to alter their properties, this specific finding is novel. The researchers suggest this observation likely applies to a broader range of liquids beyond those tested.
“Our results indicate that if you pull a simple fluid—a flowing liquid—with enough force per unit area, it reaches what we term a ‘critical stress’ point, after which it literally breaks apart, much like a solid,” stated Lima. “And this is probably true for all simple liquids, including common ones like water and oil.”
One of the next research avenues will be deciphering the mechanisms underlying this process. The team found that liquid fractures propagate extremely rapidly once initiated, at speeds between 500 and 1500 meters per second.
This fracture speed is consistent with cavitation—a phenomenon theoretically debated for decades. The hypothesis suggests that sufficient stress within the liquid generates a microscopic vacuum bubble, which in turn facilitates the liquid’s rupture.
As these experiments indicated, the process is so fast that capturing high-quality imagery presents a challenge. Now that compelling evidence exists for this behavior, scientists have more substance to investigate.
Future work must examine how such fractures might occur in other liquids and outside strictly controlled laboratory settings. The researchers cited two real-world application areas where these findings might prove beneficial.
As scientific methods and investigative instruments advance, liquids continue to reveal their hidden properties and underlying physical principles, suggesting there is likely much more yet to be discovered.
“Now that we’ve reported this unforeseen behavior, a crucial next step is to fully comprehend the root causes and how this behavior manifests across other liquids,” Lima concluded. “It will also be interesting to see how this discovery can be leveraged to improve fiber spinning processes and other applications involving viscous materials.”
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