Chapter 5 Wetting and its Modification by Surfactants

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Chapter 5 Wetting and its Modification by
Surfactants
2006.4.12.
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1. Wetting process and contact angle.

• Wetting
• Wetting is a familiar surface phenomena
• e.g. Polyester and cellulose acetate films
• Plant leaves and pesticides
• Wetting and waterproofing of fabrics
• cleaning and antirust of metals
• (2) Wetting process is application of adsorption
  on solid/fluid medium

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• (3) What is the Wetting process ?
• One fluid(L or G) is replaced with another
  on solid(S)/fluid(L or G).
• 2. Contact Angle??? (?) and Young ??equation
• Definition when a fluid drop reach spreading
  equilibrium on the interface of solid/fluid, the
  angle ? rotated to pass through the fluid
  from the tangent of G/L interface to interface of
  solid/fluid, used the point o as a centre of a
  circle, is the contact angle of this fluid on
  this interface.

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• (2) ? and wetting
• ?lt90º wetting ?0º full wetting
• ?gt90º no wetting ?180º full no wetting
• (3) Youngs eq. 1805 Young found
• ?SV ?SL ?LV cos? or cos? (?SV -
  ?SL)/ ?LV
• ?SV?, cos? ?, ? ?? ?LS?, cos? ? , ?
  ??
• 3 Wetting process
• Adhesional wetting process(??)
• (a) G/S G/L ? L/S
• -?G ?SV ?LV - ?SL
• WSL? 0
• WSL - Adhesional wetting work
• (b) Relation with ?

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• -?G WSL ?LV(1cos ?) ? 0
• cos ? ? -1,
• ? ? 180º Adhesional wetting
• ? ? 180º no Adhesional wetting
• (2) Immesional wetting process (??)
• Hard solid surface
• G/C ? L/S
• -?G ?SV - ?SL Wi A ? 0
• Wi - Immesional wetting work
• A - adhesional tension, driving force of
  spreading process
• Relation with ? -?G ?LVcos ? Wi A ?
  0
• ? ? 90º immesional wetting ? ? 90º no
  immesional wetting

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• (b) Soft (porous) solid surface
• G/C ? L/S capillarity
• penetration pressure or addition pressure
• ?P 2 ?LV/R 2?LVcos ?/r 2(?SV -
  ?SL)/r
• R curvature radius of surfacer Radius of
  capillary
• gt 90º, ?P lt 0 no penetration ? lt 90º, ?P gt0
  penetration
• r ?, ?SV?, ?SL?, or if ?LV?, then ??, ?P ?

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• (3) Spreading wetting process (??)
• G/C ? L/S new G/L
• -?G ?SV - ?SL - ?LV S ? 0
• S Spreading Coefficient
• S ?SV - ?SL - ?LV ?SV - ?SL ?LV - 2
  ?LV
• WSL WAA
• WAA 2 ?LV the cohesion work of liquid
• (b) Relation with ?
• -?G ?LV (cos?-1) S ? 0
• ? ? 0º Spreading wetting
• ? ? 0º no Spreading wetting

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• (4) Adhesional tension and three type of wetting
• Adhesional tension A ?SV - ?SL
• Power replacing gas with liquid on
  solid(S)/fluid(L or G).
• WSL ?SV - ?SL ?LV A ?LV , ? ? 180º
• Wi ?SV - ?SL A , ? ?
  90º
• S ?SV - ?SL - ?LV A - ?LV, ?
  ? 0º
• (b) driving force of spreading process
• ?SV?, ?SL ?, A ? wetting ?
• (c) ?LV surface tension of liquid
• ?LV?, spreading wetting? ?LV ?, Adhesional
  wetting?
• cos? A /?LV, if Agt0 , ?LV?, cos? ?, ? ?

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4. Mensuration of contact angle (1) Angle measure
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(2) Sloping plate(???)
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(3) Height measurement (?????)
sin? 2hr/(h2r2) or tg(?/2) h/r
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(4) Suspender(???)
Sin ? 1 - ?gh2/2?LV
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(5) powder method h2 Cr?LVcos? t/2? Cr
constant t time (s) ? - viscosity of liquid
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5. Contact angle hysteresis (1) Hysteresis ?2-
?1 ? 0 (?2 gt ?1 )
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• (2) Factors affecting the hysteresis
• Surface roughness (???)
• Youngs eq. ?SV - ?SL ?LV cos?0
• Surface roughness r(?SV - ?SL) ?LV cos?W
• Wentzel eq. roughness r cos?W/cos?0gt 1
• Wetting solid surface 0 lt ?0 lt 90
• cos?W gt cos?0, ?W lt ?0
• r?, ?W ?
• No Wetting solid surface 90 lt?0lt 180
• r?, ?W ?

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• (B) Surface non-uniformity
• Advancing angle - the wettability of the lower
  surface energy area.
• Reversing angle - the wettability of the higher
  surface energy area.

The curves about ? of water on the mixed monofilm
of TiO2 and C18H37N(CH3)3Cl, and rate of TiO2
overlay
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• (C) Other
• Temperature ?T 10 ?? 0.20
• Viscosity? equilibrium time ?
• 2. Wettability of solid surface
• From Youngs eq. Cos ? (?SV - ?SL)/ ?LV
• If ?SV ?, and ?SL ?, then ??,
• but the measurement of ?SV is very difficult
• Generally ?LV ?100mJ/m2 (water 72.8mJ/m2)
• Low energy surface ?SV ?100mJ/m2
• High energy surface ?SV 100-5000mJ/m2

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1.Low energy surface(LES) and critical surface
tension(?c) (1) The solid of LES PP, PET, PTFE
etc. (2) ?c the maximum surface tension of the
liquid spreading on low energy solid
surface.
?c lim ?LVcos?
??0
Zisman plot of
Zisman plot of homologous compound
non-homologous compound
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(3) ?c ?, wettability ?, if ?c ? ?LV then can
spreading

• (4) Facts of affecting ?c
  
  
• Element of materials
• F lt H ltCl lt Br lt I lt O lt N
• Surface mono-film of materials (to see table 5-2)

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• 2. High energy surface(HES) and self-repel(??)
• (1)The solids of HES wool, cotton, glass, metal
  oxide, sulfide(???) ect.
• ?SVgt100mJ/m2 gt ?LV, generally ??0 of liquids on
  it
• (2) Self-repel liquids e.g.
• octanol (??), n-octanoic acid (???)
• can not spread on high energy surface
• 3. The wetting of surfactants
• (1)Low energy surface
• ?SL?, ?LV ?(?LV lt ?C), then spread aq. on surface

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• (2) High energy surface
• (a) same charge with surface orientation
  adsorption of hydrophobic groups wetting
• (b) opposition charge with surface
• orientation adsorption of hydrophilic groups no
  wetting
• adsorption of hydrophobic interaction wetting

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• 4. Evaluation of surfacial energy
• Fowkes model
• ? ?d ?h ?m ?? ?I
• d dispersion force
• h hydrogen bond
• m metallic bond
• ? - ? electric interaction
• dispersion force is a interaction
  ubiquitous, long distance, attract force

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• (2) L/L interfacial tension ?ab
• ?ab ?a ?b 2(?ad ?bd)1/2 2(?ap ?bp)1/2
• ?a, ?b surface tension of liquid a and
  b
• ?ad, ?bd contribute of dispersion force
• e.g. ?Hg/W ?HgLV ?WLV 2(?Hgd ?Wd)1/2
• 484 72.8 2(21.8?200)1/2
• 424.8mJ/m2 426mJ/M2
  
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  (experimental value )
• (3) S/L interfacial tension ?SL
• ?SL ?S ?LV 2(?Sd ?Ld)1/2

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• 5. Wetting agents
• Characters of Structure
• branched chain e.g. Surfynol 104, AOT
• short straight chain e.g. JFc C7-9OEO5-6
• Anionics and Nonionics
• (2) Application of wetting process
• Ore floatation(????)collectors foaming agents
• Waterproof Oil repel of fabics
• Antirust Corrosion mitigation