The classical Wenzel equation was modified to extend it to 3-dimensional structures which enables us to quantitatively predict the contact angle of a periodic structure.
The results of the contact angles calculated from the 3-dimensional Wenzel equation agreed well with the results measured on the nano-periodic structures.
Although the same material is used, the contact angle can be controlled over a range of more than 100° by changing the dimensions of the nano-periodic structures.
The threshold levels of the pitch and depth of these periodic structures for switching the wettability from hydrophobic to hydrophilic were clarified experimentally.