We describe how a wetting liquid brought into contact with a forest of micropillars impregnates this forest. Both the driving and the viscous forces depend on the parameters of the texture (radius b and height h of the pillars, pitch p of the network) and it is found that two different limits characterize the dynamics of wicking. For small posts (h < p), the film progresses all the faster since the posts are high, allowing a simple control of this dynamics. For tall pillars (h > p), the speed of impregnation becomes independent of the pillar height, and becomes mainly fixed by the radius of the posts.

We consider microscopic contact states of a drop deposited on textured rough surfaces. The energies of three possible (meta)stable wetting states are compared and the lowest energy state is regarded as the “phase”. We present the “phase diagrams” in the two-dimensional space of texture parameters, which suggests transitions between the wetting states. We propose a model which allows the description of transition states between (meta)stable contact states and quantify the energy barriers between them. Thereby, we theoretically suggest that the actually realized state is not always the lowest energy state.

We consider the quasi-static energy of a drop on a textured hydrophilic surface, with taking the contact angle hysteresis (CAH) into account. We demonstrate how energy varies as the contact state changes from the Cassie state (in which air is trapped at the drop bottom) to the Wenzel state (in which liquid fills the texture at the drop bottom) assuming that the latter state nucleates from the center of the drop bottom. When the textured substrate is hydrophilic enough to allow spontaneous penetration of liquid film of the texture thickness, the present theory asserts that the drop develops into an experimentally observed state in which a drop looks like an egg fried without flipped over (sunny-side up) with a well-defined radius of "the egg yolk." Otherwise, the final contact state of the drop becomes like a Wenzel state, but with the contact circle smaller than the original Wenzel state due to the CAH. We provide simple analytical estimations for the yolk radius of the "sunny-side-up" state and for the final radius of the contact circle of the pseudo-Wenzel state.

The wettability of textured surfaces is strongly dependent on the contact state of a small drop deposited on them. We consider transitions via nucleation between two representative contact states of Cassie and Wenzel when there exists hysteresis in the contact angle. We find that the effect of the hysteresis is significant: a drop can be trapped by various states which are neither Cassie nor Wenzel states in the conventional sense.