Slanted high‐aspect‐ratio polymer pillars are studied for their unique properties such as unidirectional spreading of liquid, directional adhesions, or alignment of cells, where the pillars are in constant contact with water or in a humid environment. These pillars, however, tend to cluster upon water evaporation due to the capillary force and lowered modulus of the pillars. Here, spontaneous recovery of clustered slanted hydrogel pillars to their original shape is presented by exploiting the modulus change of hydrogel materials during water evaporation. The clustering and recovery of the slanted hydrogel micropillars are monitored in situ by optical microscopy and environmental scanning electron microscopy. To elucidate sequential clustering and recovery mechanism, the adhesion force between the pillars and the restoring force is compared. Finally, the dynamic change of optical transparency is exploited as the result of switching between clustering and recovery of the slanted micropillars for display. The study of the deformation and recovery of slanted hydrogel pillars will offer insights into geometrical and material designs in water‐based applications.

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Superomniphobic surfaces inspired by nature have been studied for decades. Recently, the development of liquid-repelling surfaces has moved from the fabrication of artificial structures to real applications that address friction associated with clothes, paper, and skin. To have superoleophobicity, re-entrant structures such as mushrooms or inverse trapezoids have been suggested. However they can be mechanically fragile, especially under shear stress, because the bottom region is narrow. Here, a facile method to obtain new re-entrant structures is proposed, namely, micro-hyperbola structures, by wetting a photocurable viscous liquid around micropillars by capillary force. It is demonstrated that the formation of the hyperbola structures depends on the spacing ratio between micropillars, and the formation mechanism is explained with a simple model. The micro-hyperbola structure demonstrates robust omniphobicity even after rubbing and abrasion tests. The advantage of the wide fabrication range and the robust superoleophobicity of micro-hyperbola structures enable the uses in practical superomniphobic applications that undergo shear forces.

Cracks are common in nature. Cracking is known as an irreversible and uncontrollable process. To control the cracking patterns, many researchers have proposed methods to prepare notches for stress localization on films. In this work, 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. 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 relationship with the film thickness can guide the study of cracking phenomena.

In article number 2010053, Kee‐Youn Yoo, Hyunsik Yoon, and co‐workers propose a facile method to obtain new re‐entrant structures, namely, micro‐hyperbola structures, by wetting a photocurable viscous liquid around micropillars by capillary force. The micro‐hyperbola structure demonstrates robust omniphobicity even after rubbing and abrasion tests. The robust superoleophobicity of the micro‐hyperbola structures enables their use in practical superomniphobic applications that undergo shear forces.