title: Direct observation of internal fluidity in a water droplet during sliding on hydrophobic surfaces.
abstract: In the current study, we used a high-speed camera system with particle image velocimetry to observe the internal fluidity of water droplets during sliding. The droplets' velocity during sliding was controlled by slipping and rolling motions. On the superhydrophobic surface, with a contact angle of 150 degrees, the droplet fell at high velocity by slipping. However, on a normal hydrophobic surface whose water contact angle was around 100 degrees, both slipping and rolling controlled the droplet's velocity during sliding. In addition, the advancing velocity might be large when the slip velocity is large and the contact area is small.
authors.affiliation: Kanagawa Academy of Science and Technology, Kawasaki-shi, Kanagawa 213-0012, Japan.
authors.forename: Munetoshi
authors.initials: M
authors.lastname: Sakai
authors.forename: Jeong-Hwan
authors.initials: JH
authors.lastname: Song
authors.forename: Naoya
authors.initials: N
authors.lastname: Yoshida
authors.forename: Shunsuke
authors.initials: S
authors.lastname: Suzuki
authors.forename: Yoshikazu
authors.initials: Y
authors.lastname: Kameshima
authors.forename: Akira
authors.initials: A
authors.lastname: Nakajima