1. §8.2 Surface phenomenon of liquid
8.2.3 wetting and spreading

2. 8.2.3 wetting and spreading g-l + g-s  s-l
1. Some definitions
(1) adhesion
g-l + g-s  s-l
G = s-l – (g-l + g-s) = -Wa g S l
Work of Adhesion
Wa = g-l + g-s – s-l
Wa > 0
The solid can be wetted by the liquid.

3. g-s  s-l (2) immersion G = s-l - g-s = -Wi
Wi = g-s - s-l > 0
Work of immersion

4. (3) spreading
g-s  s-l + l-g
G = s-l + l-g - s-g = -S
spreading coefficient
S = s-g - s-l - l-g > 0
The liquid spreads over the solid spontaneously.

5. 2. Contact angle ()

6. The contact angle () is the angle measured through the liquid, where a liquid/vapor interface meets a solid surface
goniometer
Hydrophobicity of conversion layer on Mg alloy

7.  g-l g-s s-l The direction of surface tension Under equilibrium:
g-l cos  + s-l = g-s
Young equation
When :g-s - s-l = g-l , cos =1,  = 0 o, Complete wettable.
When :g-s-s-l< g-l , 0<cos <1, <90 o, wettable.
When :g-s < s-l , cos < 0,  > 90 o, nonwettable.

8. 3. Lyophobic and lyophilic solids
The greater the specific energy, the easier the spreading of liquid over solid.
g-s – g-l – s-l > 0
g-l
g-s
s-l 
g-s > g-l + s-l
g-s > g-l

9. g-s > 100 mN m-1, high-energy surface : Metals, oxides, chlorides, inorganic salts. g-s  500 ~ 5000 mN m-1
g-s < 100 mN m-1, low-energy surface: organic solids, polymers. PTFE: g-s  18 mN m-1
Nonstick cooker

12. 4. Spreading over liquid SO/W = - G = W - O - W/O SO/W > 0,
oil can spread over water
SO/W < 0,
oil floats in shape of lens.
Liquids
Iso-C5H12O
C6H6
C6H12
CS2
CH2I2
SO/W
44.0
8.8
3.4
-8.2
-26.5

13. Floating oil drop on chicken soup
Floating oil on sea surface

14. 1774 Benjamin Franklin (2.4 nm)
Clapham Common (2000 m2)
1774 Benjamin Franklin (2.4 nm)
The film formed over water is of one molecule thick. (proved by Pockels and Rayleigh):
Unimolecular film, monolayer, Insolvable film

15. A environmental disaster
wreck of a tanker
Spreading of oil over seawater
A environmental disaster

16. 2010年5月5日，美国墨西哥湾原油泄漏事件

17. Capillarity
Capillary rise / depression

18. Discussion

19. p Measurement of porosity distribution: Mercury method
This relation can be used to determine the surface tension of liquids – capillary rise method