High‐speed optical imaging of liquid film flow and liquid macro‐ slip over free surfaces with different surface energies

M. Polajnar, B. Bizjan, B. Širok, M. Kalin

Lubrication Science (2017) 0: 1-10.

Abstract

High‐speed optical imaging is introduced as a visualization method to investigate the film‐flow properties of liquids with different surface tensions and viscosities (water, poly‐alpha‐olefin oil, and glycerol) over free rotating surfaces with different surface energies and polarities (steel, and two different diamond‐like‐carbon ‐ DLC coatings, i.e. DLC, and F‐DLC). It was found that the polar surface energy strongly influences the structural dynamics of the liquid film's flow and the film's slip. Namely, a decrease in the polar surface energy results in a less stable film with de‐wetting areas and breakups into streams, as well as in a larger amount of film slip, which was most clearly expressed by the F‐DLC. It was also found that the combination of a high surface tension and a low viscosity provides the largest amount of liquid slip, with the most obvious breakup of the liquid film being observed with water, which clearly exhibits these properties.

Keywords: High‐speed optical imaging, Liquid slip, Surface energy, Surface tension, Viscosity

URL: http://onlinelibrary.wiley.com/doi/10.1002/ls.1388/pdf

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