Regensburg 2013 – scientific programme

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DY: Fachverband Dynamik und Statistische Physik

DY 16: Pattern Formation

DY 16.7: Talk

Wednesday, March 13, 2013, 11:30–11:45, H46

Looking beneath the surface: A study of desiccation cracks over patterned substrates — •Pawan nandakishore and Lucas Goehring — Max Planck Insititute for Dynamics and Self Organization, Goettingen, Germany

From cracks on planetary surfaces to cracks in dried paint, to cracks in microscopic thin films, contraction cracks occur at many length scales and, following linear elasticity theory these patterns should scale across these length scales. We investigate the crack patterns formed due to the presence of sinusoidal substrates and substrates with a single peak or trough. To this effect, we look at desiccated mud cracks by drying a bentonite slurry over the different substrates. The relevant parameters in this problem are the layer height, wavelength and amplitude of the substrate. We characterize the topology of the pattern, and show that an order parameter, characterized by the orientation of the cracks, behaves non monotonically. At low layer heights the crack pattern is disordered and contains wavy cracks. As the layer height is increased, a highly anisotropic crack pattern is formed when the wavelength matches the natural crack spacing of the film, or close to the layer thickness. This pattern is characterized by cracks that run parallel and perpendicular to the substrate. When the layer height is further increased the pattern becomes disordered however there are no wavy cracks present. Combining these observations from the sinusoidal substrates and the observations from the single peaks and troughs we attempt to acquire a means to decipher what lies beneath the crack pattern.