§8.5 Surfactants and their properties
and Applications
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
§8.5 Surfactants and their properties and Applications
8.5.1 Surfactants
§8.5 Surfactants and their properties and Applications
(2) Classification of surfactant
(1) Classification by structure/active moiety
Group work:Find at least one example for
each type.
8.5.1 Surfactants
§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
Organosilicon surfactant
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
nS Sn
Rod-like micelleLayered micelle
An equilibrium exsits between
micelle and individual surfactant
Micelles are usually charged.
8.5.2 Critical micelle concentration and micelle
§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 40 oC.Done in our research group.
8.5.2 Critical micelle concentration and micelle
§8.5 Surfactants and their properties and Applications
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
Medium cmc Aggregation
number
Average charge
per micelle
Water 0.0081 80 14.4
0.02 M NaCl 0.00382 94 13.2
0.10 M NaCl 0.00139 112 13.4
0.40 M NaCl 0.00052 126 16.4
Effect of electrolyte on cmc and micelle
8.5.2 Critical micelle concentration and micelle
§8.5 Surfactants and their properties and Applications
What is the effect of Na2SO4 in detergent powder?
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
§8.5 Surfactants and their properties and Applications
Cr3+ + 3OH- = Cr(OH)3
(3) Phase transfer (extraction)
8.5.3 Important application of surfactants
§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
§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
§8.5 Surfactants and their properties and Applications
Separation of oil from water.
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 thesmoke 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) 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
8.5.3 Important application of surfactants
§8.5 Surfactants and their properties and Applications
The way for soap bubbles
intercepts with each other.
(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
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