Painting and Growing Crystals with the Rayleigh-Plateau Instability

We use the Rayleigh-Plateau instability to fabricate structures in a 3D printing context. We deposit threads of glycerol in an immiscible polymeric bath. Owing to capillary effects these threads break into a collection of drops. As the polymer cures, these drops are permanently captured into the matrix, thereby forming a composite material. We show how the printing operation conditions (trajectory, nozzle speed, flow rate, etc.) and fluid properties affect the breakup dynamics and eventually select the drop size and breakup wavelength. In addition, by tuning the spacing between successive threads, we are able to fabricate crystal-like structure in these composite materials. The pattern formation process is robust: the crystal structure exhibits the self-healing of initial or accidental defects. Existing theories (for example, spatiotemporal stability analysis) are adapted to our problem so as to rationalize our experimental results. In turn, we aim to take advantage of our model for the directed control of the instability toward the design of materials with prescribed properties and functions.