Directionality of Anisotropic Wicking on Mesoporous Surfaces Obtained by Poisson Effect-Manipulated Crack Formation

Wicking is the rapid spreading of water through a combination of capillary wicking and evaporation when it comes into contact with a porous material. This phenomenon has practical applications in everyday life, such as in performance clothing that absorbs sweat and quickly evaporates it. In recent years, the study of directional wicking has led to breakthroughs in areas such as heat transfer, colorimetric devices, energy-harvesting devices, and microfluidics.<br/>In this study, we present the wicking of anisotropic strips induced by mesoporous TiO2 colloidal films. Anisotropic strips are obtained by converting cracks in the micro-pyramidal array into anisotropic cracks. When an elastomer block with an array of micro-pyramids is stretched, the period of the force increases in the direction of stretching and decreases in the perpendicular direction due to the Poisson effect. This increases the difference in the angle of the pyramid edges between the part parallel to the stretching direction and the part perpendicular to it. Consequently, this angular difference induces anisotropic cracking by concentrating stresses at sharp notches. This suggests a method for fabricating mesoporous strips consisting of nanoparticles with TiO2 mesoporous microchannels, which have potential applications in various fields, including microfluidics, displays, colorimetry, and photocatalytic microchannels.