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Chapter 2 Adsorption of Surfactants at Interface

Chapter 2 Adsorption of Surfactants at Interface. 2006.3.18. 增溶 作用. 胶束 作用. 气液 界面. 泡沫. 表面 活性. Gibbs 吸附方程. 液液 界面. 洗涤 作用. 乳液. 吸附 作用. 表观吸 附方程. 润湿. 固液 界面. 分散. 表面电位. 吸附机理. §1. The surface excess concentration and the Gibbs adsorption equation. About adsorption

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Chapter 2 Adsorption of Surfactants at Interface

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  1. Chapter 2 Adsorption of Surfactants at Interface 2006.3.18.

  2. 增溶 作用 胶束 作用 气液 界面 泡沫 表面 活性 Gibbs 吸附方程 液液 界面 洗涤 作用 乳液 吸附 作用 表观吸 附方程 润湿 固液 界面 分散 表面电位 吸附机理

  3. §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

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

  5. 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

  6. (2) Surface excess concentration • If total mole number of i component : ni0 (b) The concentration of 、 phase Ci Ci and Ci >Ci (c) The boundary surface ss total volume of 、 phase : V,V ni = Ci V +Ci V (d) Surface excess ni = ni0- ni=ni0- (Ci V +Ci V)

  7. (e) Surface excess concentration i= ni/A A – area of ss-surface 意义：单位表面积上i 组分的摩尔数比本体相中相同数量溶剂所含i 组分摩尔数的超量。 对于表面活性剂：稀溶液区，Ci Ci  1, 即i 组分在吸附界面上，单位面积的摩尔数。 i= ni/A = [ni0- ni]/A =[ni0- (Ci V +Ci V)]/A ni0 /A

  8. 2. Gibbs adsorption equation • Thermodynamics Mono-component: U=TS-PV Multi-component: U=TS-PV +ini In surface phase: U =TS -PV +ini + A

  9. Total differential: dU =TdS + S dT - PdV - VdP +i dni +ni dI + dA + A d ………………① Thermodynamic equation dU =TdS - PdV +i dni + dA ………② ①-②, then S dT - VdP +ni di + A d = 0 ( )TP ni di + A d = 0 or d = -[ni /A]di d = -idi

  10. 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

  11. (b) Gibbs equation 2(1)= -(1/ RT)d/dlna2= -(a2/ RT)d/da2  -(1/ RT)d/dlnc2 = -(c2/ RT)d/dc2 d/dc2< 0, c2,  , 2(1)> 0 positive adsorption; d/dc2= 0, c2, 2(1)= 0 no adsorption; d/dc2> 0, c2,  , 2(1)< 0 negative adsorption (c) Multi-component -d = idi = RT i(1)dlna2  RT i(1)dlnc2

  12. §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 < 10-2) 2(1)= -(1/ RT)d/dlna2= -(a2/ RT)d/da2  -(1/ RT)d/dlnc2 = -(c2/ RT)d/dc2 If (d/dc2)c2is known, 2(1)at c2 can becalculated.

  13. (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) dlna±2 = 2 R-(1) dlna±  2 R-(1) dlnc± 2 R-(1) dlnm±

  14. (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±

  15. 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)]

  16. (2) The Surface excess concentration 2(1) & (1) unit: mole/m2

  17. (3) The area per molecule A & A A = 1018/NA 2(1) (nm2) lauryl sodium sulfate十二烷基硫酸钠

  18. The area of C12H25O(C2H4O)nH(55ºC) The area of C16H33O(C2H4O)nH(55ºC)

  19. §3. Surfactants adsorption at L-L interface • 1. L-L interface • L-L two phases • Distribution of • surfactants in L-L two phases

  20. 2. Adsorption of • PEO nonionics • at coal oil-water interface • T<TP(Fig. a) • T>TP(Fig. b) • benzene • PEO in water • PPO in benzene

  21. §4. Interfacial Adsorption & Surfactivity • Efficiency(效率) and Effectiveness(效能) of Surface Adsorption • What are the Efficiency (效率) and the Effectiveness (效能) ? Efficiency(效率) – the effects produced per wastage Effectiveness(效能) – the most effects (2) Efficiency(效率) of Surface Adsorption I/ci – adsorption per-concentration Two-component Gibbs eq.: 2/c2= - (1/RT)[d/dc2] If - [d/dc2]  , then 2/c2 

  22. (3) Effectiveness(效能) 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 R>C16, then   • Hydrophilic groups: • 2/c2: Nonionics > Ionics (same R) • : Nonionics > Ionics (coulomibic repulsion) Nonionics: n↑, ↓

  23. (c) Additives • Electrolyte , Ionic Strength: I=(1/2)CiZi2 , hydrophilicity  , surface activity , 2/c2 the radius of ionic atmosphere ,  • Regulator of water structure(水结构调节剂) • 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; 

  24. 2. Efficiency(效率) and Effectiveness(效能) of Surface Tension Reduction (1) Efficiency(效率) of Surface Tension Reduction • Traube rule • Surface Pressure(表面压)  = 0 -  • Efficiency(效率) : /c2 , Efficiency (b) PC20 = - log10c  = 20mN/m , Efficiency (2) Effectiveness(效能) 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

  25. Fluorocarbons > Silicones > Hydrocarbon > Branched Hydrocarbon • Nonionics > Zwitterion > 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 C1=C20, 1 = 20mN/m; C2= CMC, 2 = CMC , then CMC= 20+xRT ln(CMC/C20) x – mole number dissociated by1 mole ionics

  26. (CMC/C20), C20 or CMC, Surface Tension Reduction > Micelle • (CMC/C20), C20 or CMC, Surface Tension Reduction < 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.

  27. Efficiency(效率) and Effectiveness(效能) of Surfactants at Interface

  28. Efficiency(效率) and Effectiveness(效能) of Surfactants at Interface

  29. Efficiency(效率) and Effectiveness(效能) of Surfactants at Interface

  30. Efficiency(效率) and Effectiveness(效能) of Surfactants at Interface

  31. Efficiency(效率) and Effectiveness(效能) of Surfactants at Interface

  32. Efficiency(效率) and Effectiveness(效能) of Surfactants at Interface

  33. CMC/C20 Ration of some Surfactants

  34. CMC/C20 Ration of some Surfactants

  35. 3. Insolubility Monomolecular Membrane • Formation of Monomolecular Film 1769’, Franklin Spread a cup of olive oil (橄榄油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

  36. (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

  37. §5. Surfactants adsorption at S-L interface 1. Adsorptive capacity and its determination from solution: (1) Adsorbents(吸附剂） (2) Adsorbate(吸附质) (3) Apparent Absorbency(表观吸附量): • = 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

  38. (2) Ion Pairing (3) Hydrogen bonding (4)Acid-Base Interaction

  39. (5) Adsorption by Polarization of  Electrons (6) Adsorption by Dispersion Forces (7) Hydrophobic bonding

  40. 3. Factors Affecting the Adsorption at S-L Interface (1) Adsorbate (吸附质) • Hydrophobic Groups hydrophobicity (e.g. R),  fluocarbon chains > siloxane > hydrocarbon chains (b) Hydrophilic Groups Ionics with different charge of interface > Nonionics > Ionics with same charge of interface

  41. (2) Temperature • Ionics: T,  • PEO Nonionics: T ,  (3) pH • Surface charge of adsorbents(吸附剂):IEP, ZEP pH, negative surface charge pH, positive surface charge (b) Charge of adsorbates(吸附质): IEP (4) Additives • Electrolyte , I=(1/2)CiZi2 , radius of ionic atmosphere , hydrophilicity  , , 

  42. Regulator of water structure(水结构调节剂) • Promoters – fructose，xylose；/c,  (small) • Breakers – urea,lower alcohol; /c,  (small) (6) Adsorbents(吸附剂） • 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;

  43. 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. • ①ion exchange • ②interaction of hydrophobic chains. The conc. Well below the CMC,-hemimicelle formation or cooperative adsorption

  44. (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.)

  45. Adsorption of dodecyltrimethylammonium bromide onto Graphon at 25ºC (0.1MNaBr aq.)

  46. (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

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