Can Sand Flow Uphill? Engineering Researchers Discover How

While the idea of sand flowing uphill may sound foreign, engineering researchers have discovered how this could be possible.

Sand Flowing Uphill?

James Gilchrist, one of the study's authors and Sam Madrid and Ruth H. Professor of Biomolecular and Chemical Engineering at the Rossin College of Engineering and Applied Science at Lehigh University, explains that after using equations to describe granular material flow, they were able to conclusively demonstrate particle movement similar to granules. However, these particles were moving uphill.

A video further demonstrates what takes place when an attractive force and torque gets applied to each sand grain. In such cases, the grains move up hills. They can move up and down the stairs and even up walls.

These unusual findings could lead to more questions and further applications in agriculture, healthcare, and material transport.

The capturing of the moment was complete serendipity during the microencapsulation research of Dr. Samuel Wilson-Whitford's, a former postdoctoral research associate from Gilchrist's Laboratory of Particle Mixing and Self-Organization. When he turned a magnet around under a vial of microrollers, which are polymer particles coated with iron oxide, the grains started moving uphill.

The researchers then tried delving further into the phenomenon. When the researchers poured micro rollers without magnetic activation, they flower downward. However, when they used a torque technique with the magnets, the particles started rotating and formed temporary doublets that formed quickly and then split. According to Gilchrist, this demonstrates cohesion that leads to a negative repose angle because of a coefficient of friction that is negative.

Boosting magnetic force also boosts cohesion, which enables grains to move faster and have more traction. The grain's collective motion and capacity to stick with each other enable a sand particle pile to collaborate in performing counterintuitive activities, such as climbing stairs or going up walls.

The researchers are now creating tiny staircases using laser cutters and documenting the ascent and descent of the materials.

Astounding Opportunities

While the study mainly focuses on the unusual uphill movement of the particles, succeeding studies will delve further into future applications and questions, including whether the microrollers may be able to climb obstacles.

The applications of such findings are far-stretching, as these microrollers can be used for moving objects, mixing things, and segregating materials. They may also be applied in microrobotics, which could then benefit the healthcare sector.

Gilchrist explains that they are conducting in-depth studies on the particles and experimenting with various rates of rotation and magnetic forces. They are doing so in order to know more about the collective motion of the particles.

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