Chapter 8. Dispersion and Flocculation of Surfactants

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Chapter 8. Dispersion and Flocculation of
Surfactants

• 2006.05.20.

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1. Introduction

• Dispersion multi-phase dispersing system
• S/G dust , smoke, and so on
• S/L suspension (???) colloids (??)
• dispersephase (???) dispersed solids
• dispersed medium (????) water
• thermodynamic unstable systems dispersants
• 2. Flocculation destabilization (???) of
  colloids
• Static interactions between colloids
• Steric interactions between colloids
• Flocculating agents or Flocculants

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2. Interfacial potential at interface of
solid-liquid

• Interface potential properties of S/L -
  electric double layer
• 1. The electrification (??) at interface of
  solid-liquid
• Ionization at interface solid-water e.g.
  proteins , ion exchange resin , etc.
• protein possess isoelectric points as IEP
• pH gt IEP to ionize anions or negative
  charge at S/L
• pH lt IEP to ionize cations or positive
  charge at S/L
• Adsorb the ions from bulk phase - in preference
  to adsorb anions or cations to electrify at S/L
• (a) Adsorption on Low Energy Surface - in
  preference to adsorb anions to possess negative
  charge. E.g. oil and

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• Fat, synthetic fibres , and carbon etc.
• Reason the cations are hydrated easier and more
  stable than anions in bulk water phase, so the
  anions are adsorbed easier than cations.
• (b) Indissoluble salts (???) Fajans rule - homo
  ions (???)are adsobed easier by ionic crystal
• e.g. AgI colloid adsorbs the Ag ion in AgNO3
  aq. to possess positive charge and the I- ion in
  KI aq. to possess negative charge.
• (c) Metallic oxide Indissoluble hydroxid e.g.
  SiO2, TiO2, ZnO2, and etc possess Zero Electric
  Point (ZEP)

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• If pH gt ZEP, then in preference to adsorb OH- to
  possess negative charge on interface S/L
• If pH lt ZEP, then in preference to adsorb H to
  possess positive charge on interface S/L
• (3) Triboelectrification (????) not only Solid
  Water but also Solid Organic medium.
• Reason according to difference electron
  affinity between(?????) two phase, the electrons
  are ejected from one phase to another.
• Dielectric constant (????) ?, electron affinity ?
• Positive charge , contrarily negative charge
• e.g. ?glass 5-6, ?benzene 2, ?water81,
  ?aceton21
• G/Water, G/aceton negative G/benzene
  positive

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• (4) Replace of crystal lattice e.g. kaoline
  (???), montmorillonite (???), etc
• Mg, Ca ? Al negative charge
• 2. Electrical Double Layer Model
• Helmholtz EDL - Plate Model
• Surface potential ?0 (4??/D) ?
• - surface charge density
• - thickness of Plate EDL, ? very little ,no
  displaying electricity , neutral ,

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• (2) Gouy-Chapman diffusion EDL
• Outline as follow
• Electrification at S/L interface,
• Counter ions as a particle in solution phase
• Diffusion EDL
• Thermodynamics potential ?0
• Interfacial potential ? ?0 e-?x
• Thickness of diffusion EDL
• 1/? (1000DkT/4?NAe2?CjZj2)1/2
• e 4.8010-10, k 1.38 10-16 erg/k
• NA 6.623 1023mol-1, D 78.3 (H2O,25C)
• ?-1 4.2010-8/(?CjZj2)1/2
  4.2010-8/(2Cj)1/2

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• (b) Disadvantage
• The point charge hypothesis
• n0- the concentration of positive and
  negative ions in bulk phase
• in diffusion layer
• Counter ions nc nn0exp(Ze?/kT)
• Homo ions nh n-n0exp-(Ze?/kT)
• If n0? and ?0 ? nc nh may be reasonless
• Only static interaction between ions and
  interfacial of solid-liquid

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• (3) Stern Model Helmholtz Gouy- Chapman
• Outline as follow
• The ions which includes hydrate water possess
  size
• Not only static interaction , but also dispersion
  force between ions and interfacial of
  solid-liquid
• Stern layer Diffusion layer
• (b) Stern layer
• IHP Inner Helmholtz Plane
• Counter ions static interaction mostly
• Homo ions dispersion force mostly e.g.
  surfactants characteristic adsorption
• Partially hydrated ions -

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• OHP Outer Helmholtz Plane hydrated counter
  ions
• (c) Diffusion Layer same with G-C Model
• (d) Surface potential
• Surface Thermodynamic Potential ?0- from S/L
  interface to bulk phase ?0 ?0(T,P)
• Surface Stern Potential ?S- from Stern Layer to
  bulk phase Diffusion potential ? ?Sexp-?x
• Adsorbed counter ions ?S lt ?0 until showing
  reversal (??)of surface potential
• Adsorbed homo ions ?S gt ?0
• ?-Potential from plane of shear at S/L to bulk
  phase electrokinetic potential

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• (e) ?S and ?-Potential
• ?-Potential can be determined, but ?S cannot.
• ?S ? ? ? the plane of shear is more far from
  the S/L interface than Stern Plane
• Small electric potential gradient (????) ?S ?
  ?
• If ion strength (I) or Stern potential (?S ) is
  low, and
• Thickness of diffusion EDL(?-1) is long, ales
  ?S ?
• (4) Zeta potential
• (a) Mensuration
• Electro-phoresis (??)
• Electro-osmosis (??)

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• (b) Factors effecting Zeta potential
• Characteristic adsorption ionics
• Electrolyte the electrical double layer is
  compressed, electric potential gradient is
  increased , and ??

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Relations of Zeta potential and ?of cationics on
bentonite (???)
Relations of Zeta potential and ?of SMP on
bentonite
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3. Dispersion of solid

• DLVO theory stability theory of colloid
• independently by Derjaguin and Landau(Soviet
  Union) in 1945 and Verwey and Overbeek (Holland)
  in 1948
• The potential energy of attraction between
  particles VA
• The potential energy of attraction between
  molecule
• Van Der Waalss energy (force) ? -??-6
• including induction (Debye) force ,
• dipole (Keesom) force , and
• dispersion (Landon) force

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• The potential energy of attraction between
  particles
• VA - (A r/12H)
• If H r as a plane particle
• VA - (A r/12?H2)
• A Apparent Hanaker constant
• A (A2)1/2 (A1)1/22
• A1,A2- Hamaker constant of particle and
  dispersion medium

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• (2) The potential energy of repulsion between
  particles
• VR (rDU2/2) ln 1exp-?H
• D dielectric consrant of dispersion medium
• U potential between adsorbed layer and
  diffusion layer
• ?-1- thickness of diffusion DEL
• (3) The Total potential energy
• V VA VR
• r ?-1
• The site of first minimum
• agglutination
• The site of second minimum
• flocculation
• VM maximum VM/kT?15-25
• stable colloid

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• Bron repulsion energy
• (b) r ?-1
• Instable VM?0
• (c) Total potential energy
• ?VA??, stability?
• ?VR??, stability?
• VT VA VR
• -Ar/12H (rDU2/2)ln 1exp-?H
• ?-1?, D?, U?, and A? then stability?
• I ?, ?-1?, ??, then stability?
• Counter Ions the radius of hydrated ions?,
  ability?
• Cations H gt Cs gt Rb gt K gt Na gt Li
• Anions F- gt IO3- gtH2PO4- gtBrO3- gtCl-
  gtClO3-gtBr-gtI-gtCNS-

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• (4) Limitations of the DLVO Theory
• The stability of lyophobic dispersion is limited
  to the effect of surface potential of the
  particles.
• A decease in the contact angle of dispersing
  medium on solid may increase dispersibility
• Surfactants that are polymeric or that have long
  POE chains may form non-electrical steric
  barriers
• In liquids of low dielectric constant,
  surfactants may produce steric barriers to
  aggregation
• For highly solvated particles in particular the
  Zeta potential may be quite different from ?s.

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• 2. Steric Forces stability and flocculation of
  polymers POE nonionicsh
• (1) An entropic effect due to restriction of
  the motion of the chains extending into the
  liquid phase when adjacent particles approach
  each other closely. When H ? ?-1, the effects
  becomes particularly important. (to see a)
• (2) A mixing ffect due to solvent-chain
  interactions and the high concentration of chains
  in the region of overlap.
• if chain-chaingtsolvent-chain, overlap, ?G?,
  dispersion if shain-chainltsolvent-chain, overlap,
  ?G?, flocculation
• (3) Both effects
• Number of adsorbed chain? effect?
• Length of adsorbed chain? effect?

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• 3. Applications
• The addition of a cationic surfactants to a
  negatively charged colloidal dispersion.
• First step cationic surfactants ?, ??,
  ??,stability? reaching to the point of zero
  charge and a minimum,
• Second step cationic surfactants??, changing to
  positive sign , ??, ??, stability?
• Third step - cationic surfactants???, compressing
  to the electrical double layer
• (2) The addition of a polymeric ionic surfactants
  to a colloidal dispersion of same sign
• First step - surfactants?, potential stability
  ?
• Second step surfactants??, plane of shear away
  from the surface ??, steric barrier?, stability
  ?

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• (3) The addition of a POE nonionic surfactants to
  an aqueous dispersion carried a small negative
  charge
• The stability increased sharply as adsorption of
  the nonionic surfactants
• The stability at this point is very high even
  when the electrical double layer is compressed by
  I? or pH?
• 4. Role of the surfactants in the dispersion
  process
• Wetting of the powder driving forcespreading
  works
• SL/S?SV - ?SL - ?LV
• Adsorption of solution surface - ?LV ? ?C gt ?LV
• Adsorption of S/L interface - ?SL ?

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• (2) De-aggregation (???) of Fragmentation (??) of
  particle clusters (??) mechanisms
• By being adsorbed in microcracks (???) in the
  solid permeation (??) to reduce self-healing
  ability particles
• ?P 2?LVcos?/R
• lt 90 ?P gt 0 then penetrable, else cannot
• cos ? (?SV - ?LS)/?LV
• Addition surfactants ?SV ?LV? cos ? ?, ? ?
• (b) By being adsorbed an ionic surfactants onto
  the particles in clusters acquire an electrical
  charge of similar sign to reduce the energy
  required to rupture solid homo-ionics gt
  nonionics gt counter ionics (instable and
  flocculation)

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• (3) Prevention of reaggregation (?????)
• (a) Reduce the thermodynamic instability of
  dispersion
• ?LS?A?, ?LS ?
• (b) Increase the dynamic stability of dispersion
• Eelectric ? Esteric ?
• 5. Dispersing of surfactants
• Aqueous dispersion
• Nonpolar powders e.g. black carbon (low energy
  surface) addition surfactants ?LV ? ?Cgt ?LV
• Charged and Polar powders e.g. metallic oxide
  (high energy surface)
• Homoions electrical barrier?????, stability ?
• Counter ions first step ????, flocculation
• second step hydrophobic adsorption,
  ????,dispersion

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• (2) non-aqueous dispersion
• Inorganic powders high energy surface
  A(A2)1/2-(A1)1/22? surface modification low
  energy surface e.g. TiO2 ZEP5.8 surface
  negative potential in neutral TiO2aluminium
  salts (positive potential) carboxylate
  surfactant (anionics) - oriented adsorption of
  hydrophilic groups the hydrophobic chains as a
  steric barrier on surface of particles.
• Organic powders low energy surface surface
  modification e.g. organic pigments stearic
  amine - oriented adsorption of hydrophilic groups
  
• Steric barrier
• Hamaker constant

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• (3) Dispersants
• Water diapersants
• Anionic naphthaline dispersants (NNO),
  lignosulfonate (??????), and polymer (polyacrylic
  acid ester)
• Nonionic Tween series, alkyl alcohol ether ,
  alkyl phenolic ether etc
• Zwitterionic amino acidic , betaine (???)
• (b) Organic medium dispersants
• Inorganic particles - aliphatic amine (???) ,
  alcohol , and organosilicon

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• (c) Super-dispersants nonaqueous e.g.
  Pigmento-philic Lyophilic (?????)system
• Characteristics and mechanism of dispersion
• M1000 10000
• Bonding groups (electrovalent bond, hydrogen
  bond, Van Der Waals force, and etc) ????
• Lyophilic chains (steric barrier, length
  10-15nm) ????
• Molecular structure
• Single functional endgroup polymers
• Double functional endgroup polymers
• A-B or A-B-A block co-polymers
• Comb(?) or Graft(??) or Random co-polymers

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• Adsorbed conformation
• Tails steric barrier
• Loops steric barrier
• Trains bonding
• 3. Flocculation
• Mechanisms of flocculation
• Neutralization or reduction of the potential at
  the Stern Layer of the dispersed particles
  addition of electrolyte electrical barrier?
  agglomeration
• Bridging (??) addition of flocculants
  flocculation
• (a) A long surfactants containing functional
  groups at various points in the molecule.

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• (b) The bridging by interaction of the extended
  portions attached to different particles may
  occur.
• 2. Flocculation
• Classes cationics , nonionics ,
• anionics , and
  zwitterionics
• (2) Properties
• Molecular weight and its distribution
• Middling MW and narrow distributionideal
  flocculants
• Middling and low MW cationics , negative
  colloid
• High MW anionics , van der Waals force
• Wide distribution cationcs flocculants

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• (b) Molecular structure
• Copolymers random , block copolymers
• Linear structure effective
• Charge density - mildness
• Macroionic (electrical potential tunnel ????)
  the counter ions can freely flow on macroionic
• (3) Flocculants
• Polymer flocculants of counter ions
• Electrical interaction ????- ????- flocculation
  
• Bridging ????- M(gt25104) charge density
• Low charge density loops tails cross
  linking
• High charge density trains no bridging

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• (b) Polymer flocculants of homo ions
• Possess positive electric charge area on negative
  solid surface
• Higher molecular weight packing ????
• Electrical potential tunnel counter ions flow
  from the bulk phase into electrical double layer
  of particles to compress the electrical double
  layer
• 3. Polymeric flocculants
• Essential condition
• Solubility in medium
• Bridging functional groups in flocculants and
  particles
• (c) Straight chain swelling conformation -
  bridging

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• (d) High molecular weight bridging
• (e) Bridging site with polymer on the surface of
  particles
• (2) Commercially available flocculants
• Cationics quaternary ammonium salt of
  poly-acrylate or poly-acrylamide, and etc
• Anionics poly-acrylic acid, poly-maleate , and
  etc
• Nonionics poly-acrylamide , PVA, and etc
• Zwitterion
• Natural polymers cationic starch (?????),
  chitosan, and etc
• Bio-polymers negative charge polysaccharide (??)