The Study of the Contact Angle and Line Tension at a Heterogeneous Surface Consisting of Alternating and Parallel Hydrophobic/Hydrophilic Stripes
Date Issued
2006
Date
2006
Author(s)
Liang, Meng-Yao
DOI
zh-TW
Abstract
Measuring the droplet diameter and advancing contact angle of water on the substrate, we can calculate the line tension of this surface by using the relation derived from modified Young’s equaton. The values of line tension in this experiment were all negative and of the order of 10-6 J/m. When a droplet laid on a specific surface consisting of alternating and parallel hydrophobic and hydrophilic stripes, while the three-phase contact line is parallel to the stripe, the line will be smooth and can be portrayed by Cassie equation(θC); while the three-phase contact line is normal to the stripe, the line will be contorted and can be described by modified Cassie equation(θMC). We prepared the alternating and parallel hydrophobic and hydrophilic self-assembled monolayers on the substrate by using the micro-contact printing. In case of silane on silicon substrate, advancing contact angle values were larger and had no tendency with decreasing line width. Because we found that silane are easy to pile up in course of micro-contact printing. In case of thiol on gold substrate, the negative line tension value would let θMC＜θC, and advancing contact angle decreases with decreasing line width, θMC：79°(2μm) →62°(0.6μm) →54°(0.4μm). Gold substrate with larger surface roughness let advancing contact angle values were smaller in this experiment. We observed the contortion of the three-phase contact line with optical microscope, the situation was not agreed with the semi-circle assumed in the modified Cassie equation.
Subjects
微觸印刷
前進角
三相線
自聚性單分子膜
線張力
micro-contact printing
advancing contact angle
three-phase contact line
self-assembled monolayers
line tension
Type
thesis
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