Stick-slip behavior of liquid droplets on pillar-arrayed PDMS surfaces
Wei, Xian
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https://hdl.handle.net/2142/72861
Description
Title
Stick-slip behavior of liquid droplets on pillar-arrayed PDMS surfaces
Author(s)
Wei, Xian
Issue Date
2015-01-21
Director of Research (if dissertation) or Advisor (if thesis)
Hsia, K. Jimmy
Department of Study
Mechanical Sci & Engineering
Discipline
Mechanical Engineering
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
M.S.
Degree Level
Thesis
Keyword(s)
Stick-Slip
Hydrophobic
Micropattern
Abstract
How the roughness of a solid impacts its wettability has been of long time interest. When a droplet moves on a rough surface, it usually undergoes a stick-slip motion. However, this phenomenon lacks a proper explanation with micro-level details and analysis. . In this study, a series of experiments were conducted to monitor the contact line (CL) evolution and resistant force over time when moving droplets over micropillar pattened surfaces. MATLAB programs were developed to analyze both force and image data. Four parameters are found to have strong correlation with a droplet’s stick-slip behavior: pillar array spacing, droplet moving velocity, liquid surface tension, and droplet volume. Further study at the CL evolution images and force-time curve revealed that the stick-slip phenomenon is synchronized with pillar pinning and depinning at the CL. The evidence of liquid residues on pillars left by passing droplet supports the hypothesis of micro-capillary bridges formation and rupture, which could be a dominant mechanism governing the stick-slip behavior of moving droplets.
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