Miracle or not? Magnetized sand flows uphill against gravity

Miracle or not? Magnetized sand flows uphill against gravity

Miracle or not? Magnetized sand flows uphill against gravity

Engineers at Lehigh University announced the discovery of a phenomenon in a statement; a phenomenon that defies conventional wisdom — sand flowing uphill.

The findings of this research, published in the journal Nature Communications, reveal a spectacle that challenges everything we thought we knew about granular materials.

James Gilchrist, the Ruth H. and Sam Madrid Professor of Chemical and Biomolecular Engineering at Lehigh’s P.C. Rossin College of Engineering and Applied Science, and one of the authors of the paper, stated, “After using equations that describe the flow of granular materials, we were able to conclusively show that these particles were indeed moving like a granular material, except they were flowing uphill.”

A serendipitous discovery

Dr. Samuel Wilson-Whitford, the lead author of the paper and a former postdoctoral research associate in Gilchrist’s Laboratory of Particle Mixing and Self-Organization, stumbled upon this extraordinary phenomenon during his research into microencapsulation.

The serendipitous nature of this revelation adds an element of wonder to the story. It all began when he introduced a magnet beneath a vial of iron oxide-coated polymer particles known as microrollers.

Under the influence of the magnet, these microrollers displayed an uncanny behavior—they began to defy gravity by moving uphill.

Wilson-Whitford, along with Gilchrist, embarked on a systematic study of this material’s response to magnetic forces under various conditions. When the microrollers were poured without magnetization, they flowed downhill. 

However, on applying torque using magnets, each particle was observed to rotate, forming temporary doublets that exhibited cohesion and resulted in a negative angle of repose due to a negative coefficient of friction. 

“Up until now, no one would have used these terms. They didn’t exist. But to understand how these grains are flowing uphill, we calculated what the stresses are that cause them to move in that direction,” elaborated Gilchrist. 

“If you have a negative angle of repose, then you must have cohesion to give a negative coefficient of friction. These granular flow equations were never derived to consider these things, but after calculating it, what came out is an apparent coefficient of friction that is negative.” 

A world of possibilities

Increasing the magnetic force increases the cohesion, giving grains more traction and speed to their movement. The collective motion and adhesion among the grains enable piles of sand particles to collaboratively perform surprising feats, such as flowing up walls and climbing stairs. The team is analyzing the movement of material across tiny staircases built using a laser cutter. 

“This first paper just focuses on how the material flows uphill, but our next several papers will look at applications,” said Gilchrist. “Part of that exploration is answering the question, can these microrollers climb obstacles? And the answer is yes.” 

The applications of this discovery appear boundless. Microrollers could revolutionize industries by changing the way we mix things, segregate materials, and move objects. This revelation could also open up new vistas in micro-robotics and revolutionize healthcare. 

“We’re studying these particles to death, experimenting with different rotation rates, and different amounts of magnetic force to better understand their collective motion. I basically know the titles of the next 14 papers we’re going to publish,” Gilchrist enthused.

The sands of science are shifting and they are flowing in unexpected directions.

Source: Interesting Engineering

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Miracle or not? Magnetized sand flows uphill against gravity

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