Cracking is known as an irreversible and uncontrollable process. Many researchers have proposed methods to prepare notches for stress localization on films to control crack patterns. Herein, we investigate a method of controlling cracks by making microscale pyramid patterns that have notches between the pyramids. After preparing pyramid patterns consisting of colloidal particles with organic residue, we annealed them to induce volume shrinkage and cracking between the pyramids. We studied the effect of film thickness on cracking and the generation of rectangular fragments consisting of multiple pyramids. Under thin flim thickness condition, crack propagated at all notches resuliting in single separate pyramids. Under thick film thickness condition, the accumulation of film stress overcomes the stress localizaion, and only some of the notches can works for cracking with generating large rectangular fragments consisting of multiple pyramids. The area of rectangular fragments was in good agreement with the results of scaling analysis. The concept of controlling cracks by imprinting notches on a film and the relation with the film thickness can guide the study of cracking phenomena.

Cracking of colloidal films to generate rectangular fragments

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