Definition: The substances that
drastically lower the surface tension of
water even at low concentrations.
8.5.1 Surfactants
The Amphiphilicity is the basic characters
of surfactants: They have both polar and
nonpolar moieties:
Hydrophilic group, hydrophobic/lipophilic
group.
The surface tension declines steeply
even at c < 10-3 mol dm-3.
1) Structure of surfactants
c
§8.5 Surfactants and their properties and Applications
8.5.1 Surfactants(1) Classification by structure/active moiety
branched, linear, or aromatic
§8.5 Surfactants and their properties and Applications
(2) Classification on functions
Emulsifier; deemulsifier, wetting agent,
anti-wetting agent, dispersant, vesicant,
(3) Classification on molecular weight
M > 10000, polymeric surfactant.
(4) Classification on composition
Siloxane surfactants, Fluorosurfactants
Organometallic surfactant: Zn soap, Mg soap
water-soluble surfactant
oil-soluble surfactant
(5) Classification on solubility
8.5.1 Surfactants
§8.5 Surfactants and their properties and Applications
8.5.2 Critical micelle concentration and micelle
When concentration (c) below ca. 10-3 moldm-3,
most ionic surfactants in aqueous solution
display similar conductance as other strong
electrolytes.
Concentration-dependence of some
physical properties of sodium dodecyl
sulfate: between 1~2 10-3 moldm-3,
sharp breaks occur.
NaCl
C12
C14
c
0 0.2 0.4 0.6
detergence
Osmotic pressure
Surface tension
Molar conductivity
interface tension
§8.5 Surfactants and their properties and Applications
6.0x10-4
7.0x10-4
8.0x10-4
9.0x10-4
1.0x10-3
1.1x10-3
0.034
0.036
0.038
0.040
0.042
0.044
0.046
/
N m
c / mol dm-3
A result presented by a student research group
8.5.2 Critical micelle concentration and micelle
§8.5 Surfactants and their properties and Applications
In 1925, Mcbain postulated that at high concentration, surfactant molecules aggregate
to form micelle.
Small micelle
Ball-like micelle Rod-like micelleLayered micelle
An equilibrium exists between micelle and individual surfactant
Micelles are usually charged.
8.5.2 Critical micelle concentration and micelle
S Snn
§8.5 Surfactants and their properties and Applications
vesicle
8.5.2 Critical micelle concentration and micelle
§8.5 Surfactants and their properties and Applications
0 0.2 0.4 0.6
detergence
Osmotic
pressure
Surface tension
Molar conductivity
interface tension
CMC:
critical micelle concentration
The lowest concentration at which surfactant
molecules aggregate to form micelles.
Variation of the surface tension of the
solution with the sodium decanoate
concentration in 0.2 mol dm-3 Na2SO4 at 40oC.
Done in our research group.
8.5.2 Critical micelle concentration and micelle
§8.5 Surfactants and their properties and Applications
Phase diagram of surfactant-water system
0.04 0.06 0.08
20
30
40
TK
T / oC
Two-phase region
micellesolution
8.5.2 Critical micelle concentration and micelle
§8.5 Surfactants and their properties and Applications
8.5.3 Important application of surfactants
(1) wetting:
Pesticide, oil extraction, paint, etc.
§8.5 Surfactants and their properties and Applications
(2) beneficiation
8.5.3 Important application of surfactants
https://www.clariant.com/en/Business-Units/Oil-and-
Mining-Services/Mining-Solutions/Froth-Flotation
§8.5 Surfactants and their properties and Applications
(3) Phase transfer (extraction)
8.5.3 Important application of surfactants
Cr3+ + 3OH- = Cr(OH)3
§8.5 Surfactants and their properties and Applications
(4) solubilization
Lesol: an old disinfectant used
in hospital.
The solubility of benzene is 0.07 g in water,
9 g in solution containing 10% C17H35COOH.
Solubilization occur only when the
concentration of surfactant is over cmc.
8.5.3 Important application of surfactants
Micellar solubilization
Micellar solubilization (solubilization)
is the process of incorporating the
solubilizate (the component that
undergoes solublization) into or
onto micelles
§8.5 Surfactants and their properties and Applications
(5) emulsification
An emulsion is a liquid-liquid (oil-water)
suspension that is small drops of one liquid
dispersed in another liquid.
Any liquid immiscible with water is
named as oil.
Oil droplet
Strong mechanical stirseparation
8.5.3 Important application of surfactants
Why the emulsion is
not stable? How can we
improve its stability?
Oil layer
§8.5 Surfactants and their properties and Applications
(5) emulsification
8.5.3 Important application of surfactants
§8.5 Surfactants and their properties and Applications
Continuous phase / domain
O/W emulsion: oil in water
W/O emulsion: water in Oil
Bicontinuous phase
8.5.3 Important application of surfactants
§8.5 Surfactants and their properties and Applications
emulsification
Applications: emulsion polymerization, floor wax, oil extraction, oil transport, dry washing,
micro-reactor for enzyme-catalyzed reaction.
Due to the large specific interfacial area, emulsion is not stable thermodynamically.
In order to stabilize an emulsion a third substance known as an emulsifying agent
should be added.
8.5.3 Important application of surfactants
§8.5 Surfactants and their properties and Applications
demulsification
Water into oil?
gasoline + 1.5 % emulsifying agent + 25
% water.
the oil consumption can be reduced by
18.7 %, and the smoke and dust in the
exhaust gas can be reduced by 50%.
microemulsion
C16H34 + 10% C17H35COOH + KOH
emulsion (thermodynamically unstable,
opaque)
Emulsion + n-C4H9OH microemulsion
(thermodynamically stable, transparent) < 0.1
m
8.5.3 Important application of surfactants
§8.5 Surfactants and their properties and Applications
(6) Foaming and vesicant
Lower surface tension
Stiffen the film
Increase the viscosity.
8.5.3 Important application of surfactants
§8.5 Surfactants and their properties and Applications
The way for soap bubbles
intercepts with each other.
8.5.3 Important application of surfactants
§8.5 Surfactants and their properties and Applications
(7) Dispersion
Liquefaction of coal:
70~ 75 % coal powder
25 ~ 30 % water
surfactant
Paint, pigment
8.5.3 Important application of surfactants
§8.5 Surfactants and their properties and Applications
(8) detergence
Wetting, emulsification,
solubilization, frothing.
8.5.3 Important application of surfactants
§8.5 Surfactants and their properties and Applications
Common composition of a commercial detergent
1) Sodium dodecylbenzenesulfonate (surfactant)
2) Water softeners
3) Tween-80: Polysorbate 80
4) cmc: Cellulose acetate
5) fluorescent whitening agent
6) essence
8.5.3 Important application of surfactants
§8.5 Surfactants and their properties and Applications
Detergents and cleaners
Cosmetics and personal care
products
Pharmaceuticals
Plant protection and pest control
Medicine and biochemical research
Textiles and fibers
Leather and furs
Other “hi-tech” areas
Paints, lacquers and other coating
products
Foods and packaging
Paper and cellulose products
Plastics and composite materials
Metal processing
Oilfield chemicals
Mining and flotation
Chemical and other industrial
applications
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