Dyanmic behavior of water droplet on water repellent surface with low contact angle hysteresis

1. Introduction: Surface treatment technology for control of water droplet behavior is indispensable for various applications such as -TAS, automobile, and so on. Superhydrophobic surface with a water contact angle over... [ view full abstract ]

1. Introduction: Surface treatment technology for control of water droplet behavior is indispensable for various applications such as -TAS, automobile, and so on. Superhydrophobic surface with a water contact angle over 150o is known as a surface to extremely repel water. The superhydrophobicity is created by two factors, i.e., low surface energy and nanostructure. In general, the nanostructure is easily damaged by physical contact, resulting in the decrease in the water contact angle. Thus, it is required to create a novel surface that can control wetting behavior of water droplet after physical contact. Hydrophobic surface with a low contact angle hysteresis is considered to be an alternative surface to satisfy the demand due to the dewetting property. Thus, it is very important to develop a technology for creating hydrophobic surface with a low contact angle hysteresis. In this presentation, we report the preparation of water repellent surface showing a low contact angle hysteresis.
2. Experimental: Si wafer was used as substrate. The substrates were ultrasonically and photochemically cleaned. Hydrophobic surface showing low contact angle hysteresis was prepared on the cleaned substrate from a 1,3,5,7-Tetramethylcyclotetrasiloxane or octadecyltrimethoxysilane (ODS) by a chemical vapor deposition at 333 to 443 K for 6 to 72 h. Static and dynamic contact angles of the samples were estimated using a contact angle meter.
3. Results and Discussion: Fig 1 shows the advancing and receding contact angles of the samples prepared at 353 and 443 K. The averaged advancing contact angles of the samples at 353 and 443 K for 24 h were approximately 100 and 160o, respectively. The advancing and receding contact angles of the samples at 353 K increased with an increase in the treatment time. The contact angle hysteresis of the samples were approximately kept constant at 20o. In case of the samples at 443 K, the contact angle hysteresis decreased with an increase in the treatment time and became less than 10o when the treatment time was more than 12 h.
Acknowledgement
This work was partly supported by Grant-in-Aid for Scientific Research (A) (No. 16H02400) from Japan Society for the Promotion of Science.