title: Surface structure determines dynamic wetting.
abstract: Liquid wetting of a surface is omnipresent in nature and the advance of micro-fabrication and assembly techniques in recent years offers increasing ability to control this phenomenon. Here, we identify how surface roughness influences the initial dynamic spreading of a partially wetting droplet by studying the spreading on a solid substrate patterned with microstructures just a few micrometers in size. We reveal that the roughness influence can be quantified in terms of a line friction coefficient for the energy dissipation rate at the contact line, and that this can be described in a simple formula in terms of the geometrical parameters of the roughness and the line-friction coefficient of the planar surface. We further identify a criterion to predict if the spreading will be controlled by this surface roughness or by liquid inertia. Our results point to the possibility of selectively controlling the wetting behavior by engineering the surface structure.
authors: Department of Mechanical Engineering, The University of Tokyo, Tokyo, Japan.
authors: Jiayu
authors: J
authors: Wang
authors: Department of Mechanics, Linné Flow Centre, The Royal Institute of Technology, Stockholm, Sweden.
authors: Minh
authors: M
authors: Do-Quang
authors: Department of Mechanical Engineering, The University of Tokyo, Tokyo, Japan.
authors: James J
authors: JJ
authors: Cannon
authors: Department of Mechanical Engineering, The University of Tokyo, Tokyo, Japan.
authors: Feng
authors: F
authors: Yue
authors: Department of Mechanical Engineering, The University of Tokyo, Tokyo, Japan.
authors: Yuji
authors: Y
authors: Suzuki
authors: Department of Mechanics, Linné Flow Centre, The Royal Institute of Technology, Stockholm, Sweden.
authors: Gustav
authors: G
authors: Amberg
authors: 1] Department of Mechanical Engineering, The University of Tokyo, Tokyo, Japan [2] CREST, Japan Science and Technology Agency, Tokyo, Japan.
authors: Junichiro
authors: J
authors: Shiomi