科研之友
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摘要
Contact-line mobility characterizes how fast a liquid can wet or unwet a solid support by relating the contact angle Delta alpha to the contact-line speed U-CL. The contact angle changes dynamically with contact-line speeds during rapid movement of liquid across a solid. Speeds beyond the region of stick-slip are the focus of this experimental paper. For these speeds, liquid inertia and surface tension compete while damping is weak. The mobility parameter M is defined empirically as the proportionality, when it exists, between Delta alpha and U-CL, M Delta alpha = U-CL. We discover that M exists and measure it. The experimental approach is to drive the contact line of a sessile drop by a planenormal oscillation of the drop's support. Contact angles, displacements and speeds of the contact line are measured. To unmask the mobility away from stick-slip, the diagram of Delta alpha against U-CL, the traditional diagram, is remapped to a new diagram by rescaling with displacement. This new diagram reveals a regime where 1 Delta alpha is proportional to U-CL and the slope yields the mobility M. The experimental approach reported introduces the cyclically dynamic contact angle goniometer. The concept and method of the goniometer are illustrated with data mappings for water on a lowhysteresis non-wetting substrate.
- 出版日期2018-3-1
