AVS 53rd International Symposium
    Surface Science Tuesday Sessions
       Session SS-TuP

Paper SS-TuP18
Dynamic Hydrophobicity on Ultrasmooth Alkyl and Fluoroalkyl Silanes Self-Assembled Monolayer Surfaces

Tuesday, November 14, 2006, 6:00 pm, Room 3rd Floor Lobby

Session: Surface Science Poster Session
Presenter: N. Yoshida, Kanagawa Academy of Science and Technology, Japan
Authors: N. Yoshida, Kanagawa Academy of Science and Technology, Japan
S. Suzuki, Tokyo Institute of Technology, Japan
M. Sakai, Kanagawa Academy of Science and Technology, Japan
J.-H. Song, Kanagawa Academy of Science and Technology, Japan
A. Hashimoto, Kanagawa Academy of Science and Technology, Japan
Y. Kameshima, Tokyo Institute of Technology, Japan
A. Nakajima, Tokyo Institute of Technology, Japan
Correspondent: Click to Email
We prepared ultrasmooth hydrophobic surfaces with alkyl and fluoroalkyl trimethoxysilanes, by optimizing conditions such as solvent, concentration, and reaction time. The treatment procedure was as follows; a cleaned Si wafer was immersed into a trimethoxysilane solution at room temperature. After a while, the wafer was washed with CH@sub 2@Cl@sub 2@, acetone, and water, respectively, and dried at 80°C. Water contact angle (WCA), surface roughness, and dynamic hydrophobicity (sliding angle and sliding motion of water droplet) of the prepared surfaces were evaluated. For the ultrasmooth treatment with fluoroalkyl trimethoxysilanes, it was effective to use a solution of low concentration in 1,3-bis(trifluoromethyl)benzene. With alkyl trimethoxysilanes, xylene saturated with water was better as a solvent. WCA and surface roughness increased depending on the reaction time, and sliding acceleration showed the maximal value at smallest roughness. Roughness enhanced resistance forces against sliding of a droplet. On the smooth surfaces of various silanes, a water droplet slid down with constant acceleration depending on WCA. It was found that the optimized conditions gave excellent static and dynamic hydrophobicity to Si wafer surface and that the dynamic hydrophobicity was strongly affected by the surface roughness of only a few nm. It is noteworthy that the sliding angle was significantly affected by small roughness even of the order of nm and that the sliding angles on the prepared smooth surfaces were almost constant, regardless of chain length and whether alkyl or fluoroalkyl.