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Particle Dense Suspensions Lead to a Smoother Surface

Thursday, July 24, 2014
Scientists at the University of Chicago have discovered a new way to create a smooth coating of a sprayed material on a surface. Using a dense suspension of particles, their technique allows for a drop to rapidly form in an even layer on a surface.
A side view of a drop impacting a glass surface, splashing, and flattening into a single layer.
Image Credit: Physical Review Letters.
In the past, viscosity and 'wettability' affected spraying a liquid (like paint) onto a smooth surface. Wettability deals with how easily the liquid spreads across a surface: a drop of water behaves differently on a piece of steel than on teflon. A liquid that's too thick doesn't spread easily, either. This new method is less susceptible to these problems.
When the drop consists of more particles than liquid, inertia influences the post-impact spreading. The scientists remark that the particles at the edge of the drop spread out "as fast as particles at the splat's leading edge can move" and are less affected by friction against the surface. As the drop spreads, it creates a one particle thick layer where space forms between the particles. This allows clumps of particles to drag liquid between them.
A bottom view of a drop impacting on a glass surface, with t=9ms showing the way the particles spread out and create a lace like structure. Image Credit: Physical Review Letters
Because the process involves high impact speed, the inertia of the particles allows it to overcome factors like viscosity and wettability. It also allows this technique to be applied to current processes. Material manufacturing and printing immediately spring to mind, but it can also help with things as complicated as quantum dots and as simple as spraying paint.

The researchers also included an awesome video of what the particle drop looks like from below:
Posted by Singularity