1. §8.5 Surfactants and their properties and Applications

2. 8.5.1 Surfactants 1) Structure of surfactants
The substances that drastically lower the surface tension of water even at low concentrations.
The surface tension declines steeply even at c < 10-3 mol dm-3.
1) Structure of surfactants
The Amphiphilicity is the basic characters of surfactants
They have both polar and nonpolar moieties.
Hydrophilic group, hydrophobic / lipophilic group.

3. hydrophilic group hydrophobic group -COOH, carboxyl -OSO3H, sulphate
-SO3H, sulphonic acid
-NR4+, ammonium
-CH2- CH2-O-, poly-ethylene oxide etc.
hydrophobic group
(CH2)n
(CF2)n
(SiR2-O-)n
(-CH2-CH2 -CH2-O-)n

4. 2) Classification of surfactant
(1) Classification by structure
anionic
Group work:
Find at least one example for each type.
ionic
cationic
amphoteric
ester
ether
nonionic
amine
amide
nonionic-cationic
mixed
nonionic-anionic

5. (2) Classification on applications
Emulsifier; deemulsifier, wetting agent, anti-wetting agent, dispersant, vesicant,
(3) Classification on molecular weight
M > 10000, polymeric surfactant.
Find one example
(4) Classification on composition
Find one example
Organosilicon surfactant
Organometallic surfactant: Zn soap, Mg soap
(5) Classification on solubility
water-soluble surfactant
oil-soluble surfactant
Find one example

6. 8.5.2 critical micelle concentration and micelle
When concentration (c) below ca moldm-3, most ionic surfactants in aqueous solution display similar conductance to other strong electrolytes.
NaCl
C12
C14 c 
0.2
0.4
0.6
detergence
Osmotic pressure
Surface tension
Molar conductivity
interface tension
Concentration-dependence of properties for sodium dodecyl sulfate: between 1~2  10-3 moldm-3, a sharp breaks occur in the conductivity and surface tension.

7. A result presented by a student research group

8. Owing to the hydrophobic groups, surfactant is unstable in water
Owing to the hydrophobic groups, surfactant is unstable in water. It tends to approach to the solution surface with the hydrophobic groups pointing outwards.
When all the surface is occupied, how can surfactants stabilize themselves in the solution?

9. Micelles are usually charged particles
In 1925, Mcbain postulated that at high concentration, surfactant molecules aggregate to form micelle.
nS  Sn
An equilibrium exsits between micelle and individual surfactant
Small micelle
Ball-like micelle
Layered micelle
Rod-like micelle
Micelles are usually charged particles

10. vesicle

11. 0.2
0.4
0.6
detergence
Osmotic pressure
Surface tension
Molar conductivity
interface tension
CMC:
critical micelle concentration
The lowest concentration at which individual 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.

12. Phase diagram of surfactant-water system
0.04
0.06
0.08 20 30 40 TK
T / oC
Two-phase region
micelle
solution
Phase diagram of surfactant-water system

13. Average charge per micelle
Effect of electrolyte on cmc and micelle
Medium
cmc
Aggregation number
Average charge per micelle
Water
0.0081 80
14.4
0.02 M NaCl 94
13.2
0.10 M NaCl
112
13.4
0.40 M NaCl
126
16.4

14. 8.5.3 Important application of surfactants
(1) wetting:
Pesticide, oil extraction, paint, etc.

15. (2) beneficiation

16. (3) Phase transfer (extraction)
Cr3+ + 3OH- = Cr(OH)3

17. (4) solubilization lesol
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.

18. (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 stir
separation

19. Separation of oil from water.

20. Continuous phase domain O/W emulsion: oil in water
W/O emulsion: water in Oil
Bicontinuous phase
Continuous phase
domain

21. emulsification
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.
emulsion polymerization, floor wax, oil extraction, oil transport, dry washing, micro-reactor for enzyme-catalyzed reaction.

22. gasoline + 1.5 % emulsifying agent + 25 % water.
Water into oil?
gasoline % 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%.
demulsification
microemulsion
C16H % C17H35COOH + KOH
 emulsion (thermodynamically unstable, opaque)
Emulsion + n-C4H9OH  microemulsion (thermodynamically stable, transparent) < 0.1 m

23. (6) vesicant Lower surface tension Stiffen the film
Increase the viscosity.

25. (7) Dispersion Liquefaction of coal: 70~ 75 % coal powder
25 ~ 30 % water
surfactant
Paint, pigment

26. (8) detergence
Wetting, emulsification, solubilization, frothing.

27. 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