The Hydrophobicity and Adhesion of Heterogeneous Surfaces of Dual Nanometer and Micron Scale Structures
Abstract
An investigation was performed to study the effect a heterogeneous surface consisting of nanometer scale square posts patterned into micron scale checkerboard shapes had on surface hydrophobicity and water adhesion. In addition to altering surface geometries, different surface coatings were investigated. Conformal thin films of PDMS, CYTOP, and Teflon AF were made using a surface grafting technique and applied to each nano-scale and micro-scale design fabricated for this study. Both the static contact angle and the tilt angle required for a water drop to roll-off the surface were measured to determine the wetting state for a particular surface geometry. For nano-scale posts with spacing-to-width ratios below a certain threshold value, patterned into micro-scale checkerboard shapes with a spacing-to-width ratio <- I, the hydrophobicity of a surface was increased compared to a surface made of either all nano-scale features or all micro-scale features. Conversely, as the spacing-to-width ratio of the nano-scale square posts increased above the threshold value, for the micro-scale checkerboard shapes having a spacing-to-width ratio 5: I the surface hydrophobicity was reduced and water adhesion increased compared to a surface made of either all nano-scale features or all micro-scale features. The nano-scale spacing-to-width ratio threshold value that caused this behavior to occur was dependent on both post width and surface coating. Finally it was observed, that for the micro-scale checkerboard shapes having a spacing-to-width > 1, the micro-scale features dominated the wetting state regardless of the nano-scale post geometry.
Document Details
- Document Type
- Technical Report
- Publication Date
- Apr 11, 2011
- Accession Number
- ADA570531
Entities
People
- Alberto Cabral
- Lalitha Parameswaran
- Shaun Berry
- Theodore Fedynyshyn
Organizations
- Massachusetts Institute of Technology