Journal
ACS APPLIED MATERIALS & INTERFACES
Volume 4, Issue 8, Pages 4141-4148Publisher
AMER CHEMICAL SOC
DOI: 10.1021/am3008856
Keywords
directional wetting surface energy gradient; self-assembled monolayers; liquid motion; microdroplets; inkjet printing
Funding
- MicroNed, a consortium to nurture microsystems-technology in The Netherlands
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We investigate the motion of liquid droplets on chemically defined radial wettability gradients. The patterns consist of hydrophobic fluorinated self-assembled monolayers (SAMs) on oxidized silicon substrates. The design comprises a central hydrophobic circle of unpatterned SAMs surrounded by annular regions of radially oriented stripes of alternating wettability, i.e., hydrophilic and hydrophobic. Variation in the relative width of the stripes allows control over the macroscopic wettability. When a droplet is deposited in the middle, it will start to move over to the radially defined wettability gradient, away from the center because of the increasing relative surface area of hydrophilic matter for larger radii in the pattern. The focus of this article is on a qualitative description of the characteristic motion on such types of anisotropic patterns. The influence of design parameters such as pattern dimensions, steepness of the gradient, and connection between different areas on the behavior of the liquid are analyzed and discussed in terms of advancing and receding contact lines, contact angles, spatial extent, and overall velocity of the motion.
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