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§ 8.2 Surface phenomenon of liquid

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.

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§ 8.2 Surface phenomenon of liquid

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  1. Chapter 8 Surface phenomenon and dispersion system §8.2 Surface phenomenon of liquid 8.2.3 wetting and spreading

  2. 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) = -Wa Work of Adhesion Wa = g-l + g-s – s-l Wa > 0 The solid can be wetted by the liquid.

  3. (2) immersion g-s  s-l 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. g-l  g-s s-l 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

  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

  10. 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.

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

  12. 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

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

  14. 2010年5月5日，美国墨西哥湾原油泄漏事件

  15. 2.3.4. Capillarity Capillary rise / depression

  16. Discussion

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

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