Contact angle measurements in relation with surface conditions

1. Contact angle measurements in relation with surface conditions SundaravadivelRajarajan Liu Nanobionics Lab April. 27th 2010

2. Outline • Introduction • Cassie and Wenzel States • Experimental Setup • Results • Future Goals

3. Introduction • Surface wetting • Ability of a liquid to maintain contact with a solid surface • Degree of wetting and contact angle • Contact angle dependency • Strong dependency on the morphology of the surface. • Cassie and Wenzel state • Stable equilibrium state = Lower energy state

4. Microstructured Surface – Cassie and Weznel State Formulae Cassie State a b a b h h h Weznel State

5. Experimental Setup • Test the contact angle of water droplet on different surface structures • Different pitch, height and denseness of nanopillars • Objective of experiment • Test if results match with theory

6. Experimental Results • Pillar Height • Green and Blue lines • Increasing pillar height increased contact angle • Diameter of Pillars • Red and Blue lines • Increasing diameter reduced contact angle • Density of Pillars • Increasing density increased contact angle

7. Future Goals • Able to fabricate a very hydrophobic surface • Apply the concept of Electrowetting • Modifying contact angle by applying a voltage • Change contact angle at various positions of the droplet • Surface distortion causes droplet movement • Useful application in Lab-on-a-chip

8. Thank You