8.5 Surfactants, their properties and Applications

§8.5 Surfactants, their properties

and Applications

金谷, 表面活性剂化学

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


(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


8.5.2 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


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



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.


S Snn


vesicle



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.



Phase diagram of surfactant-water system

0.04 0.06 0.08

20

30

40

TK

T / oC

Two-phase region

micellesolution



8.5.3 Important application of surfactants

(1) wetting:

Pesticide, oil extraction, paint, etc.


(2) beneficiation


https://www.clariant.com/en/Business-Units/Oil-and-

Mining-Services/Mining-Solutions/Froth-Flotation


(3) Phase transfer (extraction)


Cr3+ + 3OH- = Cr(OH)3


(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.


Micellar solubilization

Micellar solubilization (solubilization)

is the process of incorporating the

solubilizate (the component that

undergoes solublization) into or

onto micelles


(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


Why the emulsion is

not stable? How can we

improve its stability?

Oil layer


(5) emulsification



Continuous phase / domain

O/W emulsion: oil in water

W/O emulsion: water in Oil

Bicontinuous phase



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.



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



(6) Foaming and vesicant

Lower surface tension

Stiffen the film

Increase the viscosity.



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) detergence

Wetting, emulsification,

solubilization, frothing.



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



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

8.5 Surfactants, their properties and Applications

Documents

Transcript of 8.5 Surfactants, their properties and Applications