|Fig. 1. Sun-Cups in my back yard. Ruler gives the scale.|
Alyssa Weasel helped me try to create a lab version of this pattern using poly (methyl methacrylate) (otherwise known as plexiglass) particles. She first used a spacer to make a controlled depth of particles (a few millimeters) on a clean glass substrate. She then heated the polymer in a few different ways. First, as a control, she heated the particles as one ordinarily cook an egg. She simply set the polymer on a hot-stage and heated it above its melting point. As one would expect, the particles melt and the result is a 'gob' of polymer.
|Fig. 2. Our beautiful setup. Top is an upside down hot stage, bottom is several aluminum spacers. In the middle is a glass slide with some plexi-glass particles on top.|
|Fig. 3. A 3D image of the polymer surface after heating.|
Obviously there is a lot going on in this simple system, and the image of figure 3 is not very good characterization. We have imaged different times and temperatures, but they do not render as well as this one (a relatively small perturbation). We are confident in the formation of the bumps, but need to do much more to actually characterize the system. We are not going to claim that the bumps we see have anything to do with the sun-cups formed in snow. But it does make the point that there is some fun to be had with the polymer particles!