Patterning of wettability using the photocatalytic decomposition of hydrophobic self-assembled monolayer on the TiO2 pattern

Abstract

We report a patterning process for an octadecylphosphonic acid self-assembled monolayer (ODP-SAM) using TiO2 patterns fabricated by a combined use of reactive sputtering and CF4 plasma etching. The ODP-SAM with the remaining outer region of TiO2 patterns can be used as a constant hydrophobic region. The photocatalytic decomposition of the ODP-SAM on TiO2 thin films can be applied to the formation of hydrophobic/hydrophilic wettability patterns. The photoresponsive wettability of TiO2 thin films with different surface morphologies was examined on films deposited under different sputtering conditions. The contact angle on the ODP-SAM/TiO2 surface was successfully changed from 134.8 to 0° by exposing the raw TiO2 surface after the photodecomposition of the ODP-SAM, whereas the contact angle on the ODP-SAM in the outer region of TiO2 patterns remained constant at 112.1°. The width of the wettability switching range of the raw surface of sputter-deposited TiO2 thin films can be controlled by changing the deposition conditions of the TiO2 thin films. Droplet generation solely through the bottom surface with wettability patterns defined by a combined use of an ODP-SAM and TiO2 patterns in a microchannel was also demonstrated.