Time lapse movie of pattern formation in a drying particulate suspension. A mixture of silicon dioxide particles and water is spread out on a horizontal glass slide, and evaporation generates a flow from the center towards the edge of the droplet. Large particles become pinned to the substrate by the fluid meniscus, and act like obstacles to the flow. Gradually smaller particles become trapped by the meniscus, and deposits grow sideways into irregular stripes. Patterns like these can be seen on the sides of muddy cars on rainy days.
This movie shows what happens when you inject a gas into a granular suspension at different injection rates. At low rates, “stick slip” bubbles emerge, followed by “temporal intermittency” where periods of continuous motion are interrupted by occasional jamming. Increasing the injection rate further produces a spectacular “coral”-like pattern, and ultimately destabilized viscous fingers appear at high rates.
A labyrinth pattern self assembles as a granular suspension dries out. The material is sandwiched between to glass plates, and fluid is withdrawn through a tube and a hole in the centre of the top plate. Fingers of air sweep up the granular material – glass beads of 100 micrometer average diameter – and produce a simply connected branching labyrinth. The constant spacing between the branches represents a balance between friction and surface tension at the interface. The initial disc is 35 cm across.