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Chapter 8 Surface phenomenon and dispersion system. § 8.2 Surface phenomenon of liquid. 8.2.3 wetting and spreading. S. g. l. 8.2.3 wetting and spreading. 1. Some definitions. (1) adhesion. g-l + g-s s-l. G = s-l – ( g-l + g-s ) = - W a. Work of Adhesion. - PowerPoint PPT Presentation
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§8.2 Surface phenomenon of liquid
Chapter 8 Surface phenomenon and dispersion system
8.2.3 wetting and spreading
g
S
l
g-l + g-s s-l
G = s-l – (g-l + g-s) = -Wa
Work of Adhesion
(1) adhesion
1. Some definitions
Wa = g-l + g-s – s-l
Wa > 0
The solid can be wetted by the liquid.
8.2.3 wetting and spreading
(2) immersion
g-s s-l
G = s-l - g-s = -Wi Wi = g-s - s-l > 0
Work of immersion
(3) spreading
g-s s-l + l-g
G = s-l + l-g - s-g = -S
S = s-g - s-l - l-g > 0
The liquid spreads over the solid spontaneously.
spreading coefficient
2. Contact angle ()
Hydrophobicity of conversion layer on Mg alloy goniometer
The contact angle () is the angle measured through the liquid, where a liquid/vapor interface meets a solid surface
g-l
g-s
s-l
Under equilibrium:
g-l cos + s-l = g-s
Young equationlg
slgs
cos
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.
The direction of surface tension
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-s > g-l + s-l
g-s > g-l
g-l
g-s
s-l
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
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
Floating oil drop on chicken soup
Floating oil on sea surface
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
wreck of a tanker
Spreading of oil over seawater
A environmental disaster
2010年 5 月 5 日,美国墨西哥湾原油泄漏事件
2.3.4. Capillarity Capillary rise / depression
1 2
2( )
lp p
h gr
grh
)(
2
21
Rr cos
gRh
)(
cos2
21
Discussion
This relation can be used to
determine the surface tension
of liquids – capillary rise
method
gRh
)(
cos2
21
Measurement of porosity distribution:
Mercury methodp