Superhydrophobicity and anisotropic wettability can be simultaneously achieved by simple groove pattern on a surface. To verify those characteristics experimentally, we fabricated the micro-grooved surfaces with four different groove widths. Static contact angles were measured with the sessile drop method to investigate the apparent wettability and wetting states. All four surfaces exhibited the static contact angles well fitted to those estimated on the Cassie-Baxter state in which favorable water-repellency was expected. The static contact angles measured perpendicular to grooves were higher than those measured parallel to grooves. This anisotropic wettability was also observed with the sliding angle at the onset of the droplet moving when the surfaces were tilted. The sliding angles measured perpendicular to grooves were much higher than those measured on the smooth surface without micro-grooves. Conversely, the sliding angles measured parallel to grooves were smaller than those measured on the smooth surface. Because the sliding angle as well as the contact angle hysteresis reflect the water-repellency, the micro-grooves clearly made the surfaces anisotropic water-repellent.

Various techniques for separating mixed oil and water have been developed for the purpose of controlling marine oil pollution and for the purification of wastewater containing oil from industrial processes. In this work, we fabricate porous polydimethylsiloxane (PDMS) capsules to develop a high-performance, selective oil absorber. A template method using a sugar cube is used to fabricate the porous PDMS structure by dissolving the sugar template after infiltrating it with the PDMS solution. A hollow capsule structure was prepared by controlling the infiltration time of the PDMS into the sugar template. Contact angle measurements revealed the highly porous surface of the PDMS capsule maximized the differences between hydrophobicity and oleophilicity, which improved the absorption selectivity of oil from water. The fabricated PDMS capsules exhibited superhydrophobic and superoleophilic wetting properties; the oil droplets were absorbed into the PDMS capsule upon contact, while the water droplets were not absorbed with a contact angle above 170˚. Since the absorbed oil can be stored in the capsule pores, the oil absorption capability per unit weight of the absorber is highly increased. The adsorption performance and recyclability of the PDMS capsules were also evaluated using various waste oils.

This study proposes a method for identifying correlations between tension and drop height for sessile droplets in a roll-toroll processing system. The effect of tension and drop height on the contact angle of a sessile droplet is presented. Design of experiment (DOE) methodology and statistical analysis are used to define a correlation between the process parameters. The contact angle is decreased while increasing tension and drop height. The influence of the tension is less significant on the contact angle compared with the effect of the drop height. However, tension should be considered as a major parameter because it is not easy to fix with roll eccentricity and compensating speed of the driven roll. The results of this study show that the effect of tension on the contact angle of a sessile droplet is more important than drop height because the drop height is fixed when the process systems are determined.