Memories In Paste Control Crack Patterns

We experimentally find that a paste, i. e., a densely packed colloidal suspension with plasticity, has memories of external mechanical fields it suffered, such as vibration and flow. We also find that the memories in pastes can be visualized as macroscopically anisotropic crack patterns which appear when we dry the pastes after the external mechanical fields are removed. These memories are sustained as microscopically anisotropic network structures of colloidal particles inside paste. The memory effect of paste can be a very useful tool for technological applications in future, because we can imprint the direction of crack propagation into pastes and control to make various crack patterns, such as cellular, lamellar, radial, ring, spiral, and so on.