A new research finding may have applications for industries ranging from biopharmaceuticals to chemical manufacturing. As published in Physical Review Letters, researchers from North Carolina State University, MIT and the University of Michigan have found that the surface texture of microparticles in a liquid suspension can cause internal friction that significantly alters the suspension’s viscosity – effectively making the liquid thicker or thinner.
“We heard about problems companies were having with pumping suspensions and became curious about what was causing these problems,” said NC State chemical and biomolecular engineering professor Lilian Hsiao, lead author of the paper. “Given the ubiquity of these types of fluids in the industry, we were surprised that no one had systematically looked at the role of surface roughness before. That turns out to be a really important factor in how these particle-laden fluids flow.”
When enough particles suspended in the liquid bump into each other, the researchers found, the friction becomes significant. The rougher the surface of the particles, the more friction they generate.
“It takes energy to pump a liquid suspension through a pipe or tube, and the friction created by interaction between particles dissipates a lot of that energy,” added Hsiao. “This dissipation slows down the movement of the suspension or, if the particles are very rough, can even stop it completely.” A video published by Hsiao demonstrates the shear thickening effect.
What’s the upshot? Industries can reduce friction in one of two ways: engineering the particles to have smoother surfaces, or increasing the amount of energy devoted to moving the suspension through the pipe. The latter comes with an important caveat, though: Adding energy to a suspension containing rough particles can cause expansion and added shear stress; past a certain point, it could lead to catastrophic clogging.
Hsiao says the team is now looking at ways to use these principles to make friction work in their favor.
“This is a fundamental advance in our understanding of the physics of suspensions in flow, and should help engineers and scientists address the manufacturing challenges that caught our attention in the first place,” she said.