Chapter 2 Adsorption of Surfactants

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Chapter 2 Adsorption of Surfactants at Interface
2006.3.18.
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1. The surface excess concentration and the
Gibbs adsorption equation

• About adsorption
• The interfaces of adsorption
• G-L surface adsorption foam
• L-L interface adsorption emulsion
• S-L interface adsorption wetting, dispersing
• (2) Surface active and adsorption
• Surface active ? Adsorption on surface

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• (3) Tow type in surface adsorption
• Orientation adsorption of hydrophobic groups
• (b) Orientation adsorption of hydrophilic groups.

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• 2. Surface excess concentration
• Interface phase (or layer)
• two phases inter-dissolved
• ???
• Thickness of interface phase
• a couple of molecules 0.5nm
• in dilute solution

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• (2) Surface excess
• concentration
• If total mole
• number of i component ni0
• (b) The concentration of ??? phase
• Ci? Ci? and Ci? gt Ci?
• (c) The boundary surface ss
• total volume of ??? phase V?, V?
• ni Ci? V? Ci? V?
• (d) Surface excess ni? ni0- nini0- (Ci? V?
  Ci? V?)

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• (e) Surface excess concentration
• ?i ni?/A A area of ss-surface
• ????????i ???????????????????i ?????????
• ???????????, Ci? Ci? ? 1, ?i
  ????????,?????????
• ?i ni?/A ni0- ni/A
• ni0- (Ci? V? Ci? V?)/A
• ? ni0 /A

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• 2. Gibbs adsorption equation
• Thermodynamics
• Mono-component
• UTS-PV
• Multi-component
• UTS-PV ??ini
• In surface phase
• U? TS? -PV? ??ini? ?A

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• Total differential
• dU? TdS? S? dT - PdV? - V?dP ??i dni? ?ni?
  d?I ?dA A d? ?
• Thermodynamic equation
• dU? TdS? - PdV? ??i dni? ?dA ?
• ?-?, then
• S? dT - V?dP ?ni? d?i A d? 0
• ( )TP
• ?ni? d?i A d? 0 or d? -?ni? /Ad?i
• d? -??id?i

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• d? -??id?i
• Two-component d? -?1d?1 - ?2d?2
• ss surface uncertain! So ?i uncertain!
• (2) Gibbs method
• If solvent i 1, then ?1 0
• Gibbs eq. d? - ?2(1)d?2
• (1)-solvent 1 as frame of reference
• ?2 ?20 RTlna2
• Gibbs eq. d? - ?2(1)d?2 - RT?2(1)dlna2

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• (b) Gibbs equation
• ?2(1) -(1/ RT) d?/dlna2 -(a2/ RT) d?/da2
• ? -(1/ RT) d?/dlnc2 -(c2/ RT) d?/dc2
• d?/dc2lt 0, c2?, ? ? , ?2(1) gt 0 positive
  adsorption
• d?/dc2 0, c2? , ?2(1) 0 no adsorption
• d?/dc2gt 0, c2?, ? ? , ?2(1) lt 0 negative
  adsorption
• (c) Multi-component
• -d? ??id?i RT ??i(1) dlna2
• ? RT ??i(1) dlnc2

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2. Surfactants adsorption at G-L interface

• Calculation of ?
• ( )TP,Two-component
• ?2(1) -(1/ RT) d?/dlna2 -(a2/ RT) d?/da2
• ? -(1/ RT) d?/dlnc2 -(c2/ RT) d?/dc2
• Nonionics (c2 lt 10-2)
• ?2(1) -(1/ RT) d?/dlna2 -(a2/ RT) d?/da2
• ? -(1/ RT) d?/dlnc2 -(c2/ RT) d?/dc2
• If (d?/dc2)c2 is known, ?2(1) at c2 can be
  calculated.

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• (2) Ionics
• 1-1type ionics
• RNa R- Na
• -(d?/ RT) ?R-(1) dlnaR- ?Na(1) dlnaNa
• ?OH-(1) dlnaOH- ?H(1) dlnaH
• Very low degree of ionization , ?R-(1) ? ?Na(1)
• -(d?/ RT) ?R-(1) dlnaR- dlnaNa
• ?R-(1) dlnaR- aNa
• a? a?a-?-, ?R-(1) dlna2 2 ?R-(1)
  dlna
• ? 2 ?R-(1)
  dlnc? 2 ?R-(1) dlnm

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• (b) Electrolyte Surface excess concentration ?
• homo ion e.g. NaCl ??
• no homo ion e.g. KCl , K and Na exchange
• ? -(d?/ RT) x?R-(1) dlnm
• x?R-(1) dlnmR- x?R-(1) dlncR-
• x 1 cR-/(cR-cs)
• Cs- concentration of salt
• 1-1type finite quantity cs 0, x 2
• -(d?/ RT) x?R-(1) dlnm
• Infinity quantity cs ?, x 1.
• -(d?/ RT) ?R-(1) dlnm

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• No 1-1type ionics
• if 1mole ionics ionize to x mole positive
  and negative ions, then
• -(d?/ RT) x?2(1) dlna
• 2. Adsorption of surfactants at solution surface
• Langmuir adsorption isotherm
• ? ?0 - ?0ln(1 ? c2)
• d ?/d c2 -?0 ?/(1 ? c2)
• ?2(1) ? -(c2/ RT) d?/dc2
• (?0 / RT)? c2/(1 ? c2)
• ??(1) ? c2/(1 ? c2)

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(2) The Surface excess concentration ?2(1)
??(1) unit mole/m2
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• (3) The area per molecule A A?
• A 1018/NA ?2(1) (nm2)
• lauryl sodium sulfate???????

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The area of C12H25O(C2H4O)nH(55ºC)
The area of C16H33O(C2H4O)nH(55ºC)
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3. Surfactants adsorption at L-L interface

• 1. L-L interface
• L-L two phases
• Distribution of
• surfactants in L-L two phases

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• 2. Adsorption of
• PEO nonionics
• at coal oil-water interface
• TltTP(Fig. a)
• TgtTP(Fig. b)
• benzene
• PEO in water
• PPO in benzene

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4. Interfacial Adsorption Surfactivity

• Efficiency(??) and Effectiveness(??) of Surface
  Adsorption
• What are the Efficiency (??) and the
  Effectiveness (??) ?
• Efficiency(??) the effects produced per wastage
• Effectiveness(??) the most effects
• (2) Efficiency(??) of Surface Adsorption
• ?I/ci adsorption per-concentration
• Two-component Gibbs eq. ?2/c2 - (1/RT)d?/dc2
• If - d?/dc2 ? , then ?2/c2 ?

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• (3) Effectiveness(??) of Surface Adsorption
• ??- saturated adsorption excess concentration
• (4) Some factors of influence to them
• Hydrophobic groups
• hydrophobicity(R, or SiR or YR)?, ?2/c2
  ?
• if RgtC16, then ?? ?
• Hydrophilic groups
• ?2/c2 Nonionics gt Ionics (same R)
• ?? Nonionics gt Ionics (coulomibic repulsion)
• Nonionics n?, ???

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• (c) Additives
• Electrolyte , Ionic Strength I(1/2)?CiZi2 ?,
• hydrophilicity ? , surface activity ?, ?2/c2?
• the radius of ionic atmosphere ?, ???
• Regulator of water structure(??????)
• Promoters ? fructose,xylose ?2/c2?
• Breakers ? urea,lower alcohol ?2/c2?
• ?? no marked affect
• (d) Temperature if T?, then
• Ionics water-soluble?, ?2/c2? repulsion ?, ???
• Nonionics water-soluble?, ?2/c2? ???

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• 2. Efficiency(??) and Effectiveness(??) of
  Surface Tension Reduction
• (1) Efficiency(??) of Surface Tension Reduction
• Traube rule
• Surface Pressure(???) ? ?0 - ?
• Efficiency(??) ?/c2 ?, Efficiency?
• (b) PC20 - log10 c ? 20mN/m ?, Efficiency?
• (2) Effectiveness(??) of Surface Tension
  Reduction
• ?CMC ?0 - ?CMC ?, Effectiveness?
• (3) Some Factors of Influence to Them
• Efficiency of Surface Tension Reduction
• ??2 Efficiency of Surface adsorption

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• Fluorocarbons gt Silicones gt Hydrocarbon gt
  Branched Hydrocarbon
• Nonionics gt Zwitterion gt Ionics
• I ?, PC20?
• (b) Effectiveness(?CMC ) of Surface Tension
  Reduction
• From Gibbs Eq. d? -d? xRT??dlnC
• ?? ?2 - ?1 xRT?? ?lnC xRT?? (lnC2-lnC1)
• If C1C20, ?1 20mN/m C2 CMC, ?2 ?CMC , then
• ?CMC 20xRT ?? ln(CMC/C20)
• x mole number dissociated by1 mole ionics

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• (CMC/C20)?, C20? or CMC?, Surface Tension
  Reduction gt Micelle
• (CMC/C20)?, C20? or CMC?, Surface Ten?sion
  Reduction lt Micelle
• ?Generally ?CMC ?? , but some special case
  ,e.g.
• Branched Chain Surfactants
• branching degree ?, ?? ?, CMC ?, (CMC/C20) ?
• ? ?CMC ?
• The Branched Chain Surfactants is a Surfactants
  of Surface Tension Reduction.

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Efficiency(??) and Effectiveness(??)
of Surfactants at Interface
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Efficiency(??) and Effectiveness(??)
of Surfactants at Interface
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Efficiency(??) and Effectiveness(??)
of Surfactants at Interface
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Efficiency(??) and Effectiveness(??)
of Surfactants at Interface
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Efficiency(??) and Effectiveness(??)
of Surfactants at Interface
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Efficiency(??) and Effectiveness(??)
of Surfactants at Interface
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CMC/C20 Ration of some Surfactants
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CMC/C20 Ration of some Surfactants
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3. Insolubility Monomolecular Membrane

• Formation of Monomolecular Film
• 1769, Franklin Spread a cup of olive oil
  (???80 oleic acid) on 2000m2 of pool, than the
  wave of pool was calm immediately.
• (2) Every Stations of Monomolecular Film
• Gaseous film
• ideal gas -d?/dc - ??/?c2
  -(?-?0)/(c2-0)
• (?0-?)/c2
  ?/c2
• From Gibbs equation ?2(1) ? -(c2/ RT) d?/dc2
• 
  ?/RT ?/N0kT
• ?/N0 ?2(1) ?A kT

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• (b) Liquid film expand film(L1) condensed
  film(L2)
• L1 A 50Å2 (? - ?0)(A A0) kT
• L1?L2 transition region , condensability.
• L2 A? A b - a?
• (c) Solid film(S) A 20Å2

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5. Surfactants adsorption at S-L interface

• 1. Adsorptive capacity and its determination from
  solution
• (1) Adsorbents(???)
• (2) Adsorbate (???)
• (3) Apparent Absorbency(?????)
• x/m (C0-C)V/m mole/g
• 2. Mechanisms of Adsorption at S-L interface
• L-S Interface may be Electrified, Adsorption
  at S-L interface is comparatively complex.
• Ion Exchange adsorption

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(2) Ion Pairing (3) Hydrogen
bonding (4)Acid-Base Interaction
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(5) Adsorption by Polarization of ?
Electrons (6) Adsorption by Dispersion
Forces (7) Hydrophobic bonding
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• 3. Factors Affecting the Adsorption at S-L
  Interface
• (1) Adsorbate (???)
• Hydrophobic Groups
• hydrophobicity (e.g. R)?, ??
• fluocarbon chains gt siloxane gt hydrocarbon chains
• (b) Hydrophilic Groups
• Ionics with different
• charge of interface gt
• Nonionics gt Ionics
• with same charge
• of interface

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• (2) Temperature
• Ionics T?, ??
• PEO Nonionics T? , ??
• (3) pH
• Surface charge of adsorbents(???)IEP, ZEP
• pH?, negative surface charge
• pH?, positive surface charge
• (b) Charge of adsorbates(???) IEP
• (4) Additives
• Electrolyte , I(1/2)?CiZi2 ?, radius of ionic
  atmosphere ?, hydrophilicity ? , ??, ???

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• Regulator of water structure(??????)
• Promoters ? fructose,xylose?/c ?, ?? (small)
• Breakers ? urea,lower alcohol ?/c?, ?? (small)
• (6) Adsorbents(???)
• Adsorption from aqueous solution onto adsorbents
  with strongly charged sites
• Such substrates as wool and other polyamides at
  pH above and below their isoelectric points
• Such oxides as alumina at pH above and below
  their points of zero charge

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• cellulosic and silicate surfaces at high pH
• e.g. Ion Exchange, Ion Pairing, Hydrogen
  bonding adsorption
• S-shaped adsorption isotherm for an ionics on an
  oppositely charged substrute.
• ?ion exchange
• ?interaction of hydrophobic chains. The conc.
  Well below the CMC,-hemimicelle formation or
  cooperative adsorption

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• (b) Adsorption from aqueous solution onto
  nonpolar, hydrophobic dsorbents
• e.g. carbon and polyethylene or polypropylene

Adsorption of sodium dodecyl sulfate onto Graphon
at 25ºC(?0.1MNaCl aq.)
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Adsorption of dodecyltrimethylammonium bromide
onto Graphon at 25ºC (?0.1MNaBr aq.)
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• (c) Adsorption from aqueous solution onto polar
  adsorbents without strongly charged sites
• such as cotton, polyesters and polyamides in
  neutral solution
• by a combination of hydrogen bonding and
  adsorption or dispersion forces
• Langmuir adsorption type