Particle Professor: What’s behind particle clustering?
This column describes the forces that cause particle clusters and the reasons you may or may not want clustering to occur.
Particles, especially small particles, rarely behave independently. More often than not, a range of forces or interactions results in particles behaving more as clusters than as individuals. A classic example is flour. Cohesive forces cause flour particles to behave like clumps, which is why you need to sift (sieve) it for your favorite cake recipe. Sieving provides the mechanical energy needed to break the cohesive forces and allow the flour particles to be more free-flowing.