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The evaporation behavior of microliter (2.0 microL) and subnanoliter (0.8 nL) scale water droplets was investigated on two smooth hydrophobic and hydrophilic fluoroalkylsilane coatings prepared using chemical vapor deposition. The contact angle was constant in the second stage of evaporation for a 2.0 microL droplet on the hydrophobic coating, but it was slightly decreased in the case of a 0.8 nL droplet. The contact angle decreased gradually in the same stage of evaporation for a 2.0 microL droplet on the hydrophilic coating, but it was almost constant for a 0.8 nL droplet. These differences in evaporation behavior are expected to originate from the differences of their magnitudes and signs of line tension.

Porous ceramics with unidirectionally oriented pores have been prepared by various methods such as anodic oxidation, templating using wood, unidirectional solidification, extrusion, etc. The templating method directly replicates the porous microstructure of wood to prepare porous ceramics, whereas the extrusion method mimics the microstructures of tracheids and xylems in trees. These two methods are therefore the main focus of this review as they provide good examples of the preparation of functional porous ceramics with properties replicating nature. The well-oriented cylindrical through-hole pores prepared by the extrusion method using fibers as the pore formers provide excellent permeability together with high mechanical strength. Examples of applications of these porous ceramics are given, including their excellent capillary lift of over 1 m height which could be used to counteract urban heat island phenomena, and other interesting properties arising from anisotropic unidirectional porous structures.

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Four patterned surfaces with hydrophilic areas of different sizes were prepared using photolithography with a smooth octadecyltrimethoxysilane (ODS) hydrophobic coating. The hydrophilic area in the surfaces was aligned hexagonally with a constant area fraction. The sliding angle and contact angle hysteresis of the water droplets increased concomitantly with increasing pattern size. The increase of the contact line distortion between defects at the receding side plays an important role in this trend. The droplet sliding velocity also increased concomitantly with increasing pattern size. This trend was simulated by a simple flow model. The contribution of the interface between the ODS region and the hydrophilic area was deduced from this trend. This study demonstrated the different size dependency of the chemical surface defects for sliding behavior between the critical moment at which a droplet slides down and the period when a droplet is sliding.

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