§ 8.2 surface phenomenon of liquid
DESCRIPTION
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 PresentationTRANSCRIPT
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§8.2 Surface phenomenon of liquid
Chapter 8 Surface phenomenon and dispersion system
8.2.3 wetting and spreading
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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
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(2) immersion
g-s s-l
G = s-l - g-s = -Wi Wi = g-s - s-l > 0
Work of immersion
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(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
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2. Contact angle ()
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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
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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
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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
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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
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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
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Floating oil drop on chicken soup
Floating oil on sea surface
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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
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wreck of a tanker
Spreading of oil over seawater
A environmental disaster
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2010年 5 月 5 日,美国墨西哥湾原油泄漏事件
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2.3.4. Capillarity Capillary rise / depression
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1 2
2( )
lp p
h gr
grh
)(
2
21
Rr cos
gRh
)(
cos2
21
Discussion
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This relation can be used to
determine the surface tension
of liquids – capillary rise
method
gRh
)(
cos2
21
Measurement of porosity distribution:
Mercury methodp