| dc.description.abstract | We have studied the atypical nonionic surfactant 2-(2-Butoxyethoxy)-ethanol (BDG, C4E2) and unusual droplet wetting at the edge of a homogeneous surface. Owing to the short alkyl tail, BDG is typically regarded as a solvent completely miscible with water. However, our experimental results based on bulk (density and sound velocity) and surface properties (surface tension and contact angle) show that BDG possesses the typical feature of surfactant: a sudden slope change of the property-concentration curve. Nonetheless, the critical micelle concentration determined by the turning point is usually high, about 1 M. As a result, BDG possesses the dual nature of solvent and surfactant and can be a good cleaning solution for post-chemical mechanical polishing in semiconductor industry.
When a droplet is deposited on a flat, homogenous surface, the intrinsic contact angle depicts the wettability of liquid on solid substrates. We perform droplet wetting experiments atop cylindrical frustums. Three different regimes are observed. In the first regime, the droplet does not reach the edge and the Young-Laplace equation is followed. After the droplet reaches the edge, the contact angle continues increasing with the liquid volume due to advanced pinning. In the second regime, the apparent contact angle cannot be described by the Young-Laplace equation. Once the droplet volume (or the contact angle) exceeds a critical value, the droplet starts to invade the slanted surface with the intrinsic contact angle or falls off like avalanche. In the third regime, the latter occurs because the gravity becomes important. | en_US |