Spiral and curved periodic crack patterns in sol-gel films

Thin silicate sol-gel films with four different crack patterns Were created reproducibly by controlling the film deposition parameters. The crack geometry, periodicity, and amplitude were studied experimentally as a function of the film thickness, curing time, and temperature. Direct evidence was found that the physical interplay between stress relief through film cracking and stress relief through film warping results in sawtooth, spiral, closed loop, or straight line crack trajectories.