ENGRI1110_Lect30_Nov9_posted - Parameter: Contact Angle...

Info iconThis preview shows pages 1–15. Sign up to view the full content.

View Full Document Right Arrow Icon
Parameter: Contact Angle Parameter: Contact Angle Quantifies the hydrophobicity of the solid surface Interfacial boundaries: 1. Solid-Liquid, γ sl 2. Liquid-Vapor, γ lv 3. Solid-Vapor, γ sv 2200 θ is angle between γ sl and γ lv known as contact angle
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Young-Laplace Equation Young-Laplace Equation Relates the interfacial free energies that dictate the equilibrium state of the water drops The net horizontal component of the interfacial free energy must be zero. Then the liquid does not spread and contact angle stays constant.
Background image of page 2
poor wetting good wetting complete wetting θ > 90°C 90° > θ > 0° θ θ γ sv ls cos < 0 cos > 0 cos = > 1
Background image of page 3

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Dynamic Parameter: Hysteresis Dynamic Parameter: Hysteresis Solid/Liquid interfacial area is kept constant Contact Angles Absolute difference between angles known as hysteresis
Background image of page 4
Lotus leaf structure The decreased contact area between a particle and a rough surface. Particle is cushioned by air. Decreased contact area between liquid and surface and air is enclosed. Particles adhere to the surface of the droplet and are removed from the leaf when the droplet rolls off. 30 μ m Microreli ef of the leaf
Background image of page 5

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
The heterogeneous wetting regime assumes that on a rough surface, (d), there are gases trapped between the liquid and the solid. In one wetting regime (homogeneous) assumes that on a rough surface, (c), the liquid completely penetrates the roughness grooves There is no air trapped between the liquid and the rough surface
Background image of page 6
The energy cost to wet a hydrophobic surface with water is larger than to “wet” the solid surface with air ( γ sv < γ sl ) The liquid drop will try to minimize its contact area with the solid, leaving air pockets underneath! J. Bico et al., Europhys. Lett., 47 (2), pp. 220-226 (1999) J . Bico et al . / Colloids and Surfaces A : Physicochem . Eng . Aspects 206 (2002) 42 41–46
Background image of page 7

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Hydrophobicity: b Hydrophobicity: b A very low roll off angle exists ( α ) This can be though as a low coefficient of static friction between the liquid and the surface This phenomenon has not been well studied.
Background image of page 8
Mechanism of the Lotus-Effect Smooth neutral surface: The dirt particles are predominantly overflowed by the water-droplet. Mirco-burled hydrophobic surface: The down rolling droplet washes the dirt particles away. The particles adhere tightly to the surface
Background image of page 9

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Creating self-cleaning glass coatings. http://www.nano-products.info/nanotechnologie-autoscheiben-versiegelung.php
Background image of page 10
Lotus-Effect ® roof tile Lotus-Effect ® tie Self cleaning The development of the Lotus-Effect ® paint
Background image of page 11

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
The Lotus-Effect extended Lotus leaf engineering imitation Secondary structure
Background image of page 12
The Lotus-Effect extended Water droplet Water droplet
Background image of page 13

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
(a) Pond skater (G. remigis) walking on water and (b) SEM images of a pond skater leg showing (i) numerous oriented microscale setae and (ii) nanoscale Bhushan B Phil. Trans. R. Soc. A 2009;367:1445-1486
Background image of page 14
Image of page 15
This is the end of the preview. Sign up to access the rest of the document.

This note was uploaded on 02/10/2010 for the course ENGRI 1110 at Cornell University (Engineering School).

Page1 / 42

ENGRI1110_Lect30_Nov9_posted - Parameter: Contact Angle...

This preview shows document pages 1 - 15. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online